From 15642320a5322149c3bc647ce83264cdead09b98 Mon Sep 17 00:00:00 2001
From: 9qeklajc <tthefux@gmail.com>
Date: Sun, 23 Aug 2026 11:06:06 +0200
Subject: [PATCH] stablize reserved fee calculation

---
 docs/tinfoil-direct-integration.md            |  11 +-
 routstr/auth.py                               | 520 +++++++-----
 routstr/core/admin.py                         |  71 +-
 routstr/core/db.py                            | 122 ++-
 routstr/payment/cost_calculation.py           |  25 +-
 routstr/upstream/base.py                      | 123 ++-
 routstr/upstream/ehbp.py                      | 200 ++---
 .../test_free_response_stale_reservation.py   |  44 +-
 .../test_negative_available_balance_repro.py  | 747 ++++++++++++++++++
 tests/integration/test_payment_invariants.py  | 549 +++++++++++++
 .../test_reserved_balance_negative.py         |  94 ++-
 .../test_temporary_balances_api.py            |  37 +
 tests/unit/test_cost_response_metadata.py     |  31 +
 tests/unit/test_ehbp_finalize_payment.py      | 110 ++-
 .../test_streaming_billing_finalization.py    |  78 +-
 ui/components/temporary-balances.tsx          |  47 +-
 ui/lib/api/services/admin.ts                  |   4 +
 17 files changed, 2277 insertions(+), 536 deletions(-)
 create mode 100644 tests/integration/test_negative_available_balance_repro.py
 create mode 100644 tests/integration/test_payment_invariants.py

diff --git a/docs/tinfoil-direct-integration.md b/docs/tinfoil-direct-integration.md
index c647699a..9fcc6b00 100644
--- a/docs/tinfoil-direct-integration.md
+++ b/docs/tinfoil-direct-integration.md
@@ -438,13 +438,18 @@ Routstr returns cost info as response headers:
 
 | Header | Auth | Description |
 |---|---|---|
-| `X-Routstr-Cost-Msats` | Bearer, X-Cashu | Total msats charged for this request |
-| `X-Routstr-Cost-Usd` | Bearer | USD equivalent of the charge |
+| `X-Routstr-Cost-Msats` | Bearer, X-Cashu | Settled msats debited for this request |
+| `X-Routstr-Computed-Cost-Msats` | Bearer, X-Cashu | Computed usage cost, emitted when it differs from the settled debit |
+| `X-Routstr-Cost-Usd` | Bearer | USD equivalent of the computed usage |
 | `X-Routstr-Input-Cost-Msats` | Bearer, X-Cashu | msats attributed to input tokens |
 | `X-Routstr-Output-Cost-Msats` | Bearer, X-Cashu | msats attributed to output tokens |
 
 The client/Tinfoil SDK can read these headers from the HTTP response without
-needing to decrypt the body.
+needing to decrypt the body. A duplicate or rejected finalization can therefore
+report a zero settled debit while preserving the non-zero computed usage cost.
+Normal JSON responses use the same contract: `total_msats` and `charged_msats`
+are settled values, while `computed_msats` retains the usage calculation when
+it differs.
 
 ### Setup
 
diff --git a/routstr/auth.py b/routstr/auth.py
index a9baa9e6..0dfa38e4 100644
--- a/routstr/auth.py
+++ b/routstr/auth.py
@@ -4,6 +4,7 @@ import math
 import random
 import time
 import uuid
+from contextlib import suppress
 from contextvars import ContextVar
 from dataclasses import dataclass
 from datetime import datetime
@@ -867,6 +868,10 @@ async def pay_for_request(
             _clear_current_reservation(reservation)
         raise
 
+    # The reservation is durable; keep its lease fresh for the whole request
+    # lifetime (upstream header waits, non-streaming and streaming alike).
+    _start_reservation_heartbeat(reservation)
+
     try:
         await session.refresh(billing_key)
         if billing_key.hashed_key != key.hashed_key:
@@ -957,6 +962,84 @@ async def _validate_reservation_snapshot(
         raise RuntimeError("Billing reservation record does not match the request")
 
 
+async def renew_reservation(
+    snapshot: ReservationSnapshot, session: AsyncSession
+) -> bool:
+    """Push an active reservation's lease forward so the sweeper skips it.
+
+    ``ReservationRelease.created_at`` doubles as the lease timestamp: the
+    stale-reservation sweeper releases reservations whose ``created_at`` is
+    older than the timeout, so a long-lived stream must renew it periodically
+    or lose its reservation mid-flight (and finish uncharged, since release is
+    terminal). Returns False once the reservation reached a terminal state.
+    """
+    result = await session.exec(  # type: ignore[call-overload]
+        update(ReservationRelease)
+        .where(col(ReservationRelease.id) == snapshot.release_id)
+        .where(col(ReservationRelease.status) == "active")
+        .values(created_at=int(time.time()))
+    )
+    await session.commit()
+    return bool(result.rowcount == 1)
+
+
+# One heartbeat task per in-flight reservation, keyed by release id. Started
+# when the reservation is created and stopped when it reaches a terminal
+# state, so every request path — header waits, non-streaming, streaming — is
+# covered for its whole lifetime.
+_reservation_heartbeats: dict[str, "asyncio.Task[None]"] = {}
+
+
+def _start_reservation_heartbeat(snapshot: ReservationSnapshot) -> None:
+    """Keep an in-flight reservation's lease fresh until it is finalized.
+
+    Spawns a background task that renews the lease every third of the stale
+    timeout using its own session, so requests longer than
+    ``STALE_RESERVATION_TIMEOUT_SECONDS`` are not swept and finish charged.
+    The task stops on its own once the reservation reaches a terminal state
+    or its owning request task finishes; terminal transitions also stop it
+    explicitly. Binding renewal to the owner's lifetime guarantees the sweeper
+    can always recover a reservation whose request died without finalizing —
+    a detached heartbeat would otherwise renew it forever and lock the funds.
+    """
+    interval = max(1, settings.stale_reservation_timeout_seconds // 3)
+    owner = asyncio.current_task()
+
+    async def beat() -> None:
+        try:
+            while True:
+                await asyncio.sleep(interval)
+                if owner is None or owner.done():
+                    # Request control is gone; let the lease expire so the
+                    # sweeper can release the reservation if no terminal
+                    # transition ever ran.
+                    return
+                try:
+                    async with create_session() as session:
+                        if not await renew_reservation(snapshot, session):
+                            return
+                except Exception:
+                    logger.exception(
+                        "Failed to renew billing reservation lease",
+                        extra={"release_id": snapshot.release_id},
+                    )
+        finally:
+            _reservation_heartbeats.pop(snapshot.release_id, None)
+
+    _reservation_heartbeats[snapshot.release_id] = asyncio.create_task(beat())
+
+
+async def _stop_reservation_heartbeat(release_id: str) -> None:
+    """Cancel and await a reservation's heartbeat so no renewal overlaps
+    finalization."""
+    task = _reservation_heartbeats.pop(release_id, None)
+    if task is None:
+        return
+    task.cancel()
+    with suppress(asyncio.CancelledError):
+        await task
+
+
 async def get_reservation_snapshot(
     key: ApiKey, session: AsyncSession
 ) -> ReservationSnapshot:
@@ -968,6 +1051,60 @@ async def get_reservation_snapshot(
     return snapshot
 
 
+async def _repair_corrupt_reservation(
+    snapshot: ReservationSnapshot,
+    session: AsyncSession,
+    *,
+    decrement_requests: bool,
+) -> bool:
+    """Terminalize a reservation without subtracting uncertain aggregates."""
+    transition = (
+        update(ReservationRelease)
+        .where(col(ReservationRelease.id) == snapshot.release_id)
+        .where(col(ReservationRelease.status) == "active")
+        .where(col(ReservationRelease.key_hash) == snapshot.key_hash)
+        .where(col(ReservationRelease.billing_key_hash) == snapshot.billing_key_hash)
+        .where(col(ReservationRelease.reserved_msats) == snapshot.reserved_msats)
+        .values(status="released")
+    )
+    result = await session.exec(transition)  # type: ignore[call-overload]
+    if result.rowcount != 1:
+        await session.rollback()
+        return False
+
+    if decrement_requests:
+        for key_hash in {snapshot.billing_key_hash, snapshot.key_hash}:
+            request_result = await session.exec(  # type: ignore[call-overload]
+                update(ApiKey)
+                .where(col(ApiKey.hashed_key) == key_hash)
+                .values(
+                    total_requests=case(
+                        (
+                            col(ApiKey.total_requests) > 0,
+                            col(ApiKey.total_requests) - 1,
+                        ),
+                        else_=0,
+                    )
+                )
+            )
+            if request_result.rowcount != 1:
+                await session.rollback()
+                return False
+
+    await session.commit()
+    logger.error(
+        "Released corrupt reservation without aggregate subtraction",
+        extra={
+            "reservation_id": snapshot.release_id,
+            "billing_key_hash": snapshot.billing_key_hash[:8] + "...",
+            "reserved_msats": snapshot.reserved_msats,
+        },
+    )
+    await _stop_reservation_heartbeat(snapshot.release_id)
+    _clear_current_reservation(snapshot)
+    return True
+
+
 async def _transition_reservation_to_released(
     snapshot: ReservationSnapshot,
     session: AsyncSession,
@@ -988,7 +1125,7 @@ async def _transition_reservation_to_released(
     if transition_result.rowcount != 1:
         await session.rollback()
         existing = await session.get(ReservationRelease, snapshot.release_id)
-        return bool(
+        already_released = bool(
             idempotent_success
             and existing is not None
             and existing.status == "released"
@@ -996,6 +1133,9 @@ async def _transition_reservation_to_released(
             and existing.billing_key_hash == snapshot.billing_key_hash
             and existing.reserved_msats == snapshot.reserved_msats
         )
+        if already_released:
+            await _stop_reservation_heartbeat(snapshot.release_id)
+        return already_released
 
     values: dict[str, object] = {
         "reserved_balance": col(ApiKey.reserved_balance) - snapshot.reserved_msats,
@@ -1019,7 +1159,9 @@ async def _transition_reservation_to_released(
     result = await session.exec(release_stmt)  # type: ignore[call-overload]
     if result.rowcount != 1:
         await session.rollback()
-        return False
+        return await _repair_corrupt_reservation(
+            snapshot, session, decrement_requests=decrement_requests
+        )
 
     if snapshot.billing_key_hash != snapshot.key_hash:
         child_release_stmt = (
@@ -1033,9 +1175,12 @@ async def _transition_reservation_to_released(
         )
         if child_result.rowcount != 1:
             await session.rollback()
-            return False
+            return await _repair_corrupt_reservation(
+                snapshot, session, decrement_requests=decrement_requests
+            )
 
     await session.commit()
+    await _stop_reservation_heartbeat(snapshot.release_id)
     _clear_current_reservation(snapshot)
     return True
 
@@ -1071,6 +1216,9 @@ async def _claim_reservation_for_charge(
     )
     result = await session.exec(statement)  # type: ignore[call-overload]
     if result.rowcount == 1:
+        # The claim is not committed yet — the heartbeat must keep running
+        # until the surrounding charge transaction commits, or a rollback
+        # would restore an active reservation with no lease renewal.
         _clear_current_reservation(snapshot)
         return True
 
@@ -1078,6 +1226,70 @@ async def _claim_reservation_for_charge(
     return False
 
 
+async def _charge_reservation_rows(
+    session: AsyncSession,
+    *,
+    billing_key_hash: str,
+    key_hash: str,
+    reserved_msats: int,
+    charge_msats: int,
+    extra_billing_guards: tuple = (),
+) -> bool:
+    """Release the reserved amount and record the charge on the billing row
+    (and the child row when different) inside the caller's transaction.
+
+    Guarded subtraction replaces defensive clamping: every row must still hold
+    the full reserved amount, otherwise the whole transaction rolls back and
+    nothing is charged. A violated invariant must never silently erase the
+    aggregate reservations of sibling requests. Returns False after rollback.
+    """
+    billing_stmt = (
+        update(ApiKey)
+        .where(col(ApiKey.hashed_key) == billing_key_hash)
+        .where(col(ApiKey.reserved_balance) >= reserved_msats)
+        .values(
+            reserved_balance=col(ApiKey.reserved_balance) - reserved_msats,
+            reserved_at=case(
+                (
+                    col(ApiKey.reserved_balance) - reserved_msats > 0,
+                    col(ApiKey.reserved_at),
+                ),
+                else_=None,
+            ),
+            balance=col(ApiKey.balance) - charge_msats,
+            total_spent=col(ApiKey.total_spent) + charge_msats,
+        )
+    )
+    for guard in extra_billing_guards:
+        billing_stmt = billing_stmt.where(guard)
+    result = await session.exec(billing_stmt)  # type: ignore[call-overload]
+    if result.rowcount != 1:
+        await session.rollback()
+        return False
+
+    if key_hash != billing_key_hash:
+        child_result = await session.exec(  # type: ignore[call-overload]
+            update(ApiKey)
+            .where(col(ApiKey.hashed_key) == key_hash)
+            .where(col(ApiKey.reserved_balance) >= reserved_msats)
+            .values(
+                reserved_balance=col(ApiKey.reserved_balance) - reserved_msats,
+                reserved_at=case(
+                    (
+                        col(ApiKey.reserved_balance) - reserved_msats > 0,
+                        col(ApiKey.reserved_at),
+                    ),
+                    else_=None,
+                ),
+                total_spent=col(ApiKey.total_spent) + charge_msats,
+            )
+        )
+        if child_result.rowcount != 1:
+            await session.rollback()
+            return False
+    return True
+
+
 async def adjust_payment_for_tokens(
     key: ApiKey,
     response_data: dict,
@@ -1108,6 +1320,10 @@ async def adjust_payment_for_tokens(
     # changed the caller's original estimate.
     deducted_max_cost = reservation.reserved_msats
     model = response_data.get("model", "unknown")
+    # Failure paths log after a rollback has expired the ORM instances, so
+    # capture the identifiers as plain strings up front.
+    key_log_hash = key.hashed_key[:8] + "..."
+    billing_log_hash = billing_key.hashed_key[:8] + "..."
 
     logger.debug(
         "Starting payment adjustment for tokens",
@@ -1132,8 +1348,8 @@ async def adjust_payment_for_tokens(
                 if released
                 else "Reservation was already finalized; fallback skipped",
                 extra={
-                    "key_hash": key.hashed_key[:8] + "...",
-                    "billing_key_hash": billing_key.hashed_key[:8] + "...",
+                    "key_hash": key_log_hash,
+                    "billing_key_hash": billing_log_hash,
                     "deducted_max_cost": deducted_max_cost,
                 },
             )
@@ -1142,8 +1358,8 @@ async def adjust_payment_for_tokens(
                 "Failed to release reservation in fallback",
                 extra={
                     "error": str(e),
-                    "key_hash": key.hashed_key[:8] + "...",
-                    "billing_key_hash": billing_key.hashed_key[:8] + "...",
+                    "key_hash": key_log_hash,
+                    "billing_key_hash": billing_log_hash,
                 },
             )
 
@@ -1166,6 +1382,7 @@ async def adjust_payment_for_tokens(
             # A prior charge or release already owns this reservation. Returning
             # the calculated metadata is safe; the aggregate balances must not
             # be modified a second time.
+            calculated_cost.charged_msats = 0
             return calculated_cost.dict()
 
     match calculated_cost:
@@ -1179,75 +1396,32 @@ async def adjust_payment_for_tokens(
                     "max_cost": cost.total_msats,
                 },
             )
-            # Finalize by releasing reservation and charging max cost
-            if billing_key.reserved_balance < deducted_max_cost:
-                logger.error(
-                    "reserved_balance below deducted_max_cost before MaxCost finalization — clamping to 0",
-                    extra={
-                        "key_hash": key.hashed_key[:8] + "...",
-                        "billing_key_hash": billing_key.hashed_key[:8] + "...",
-                        "reserved_balance": billing_key.reserved_balance,
-                        "deducted_max_cost": deducted_max_cost,
-                        "total_cost_msats": cost.total_msats,
-                        "balance": billing_key.balance,
-                        "total_spent": billing_key.total_spent,
-                        "model": model,
-                    },
-                )
-
-            safe_reserved = case(
-                (
-                    col(ApiKey.reserved_balance) >= deducted_max_cost,
-                    col(ApiKey.reserved_balance) - deducted_max_cost,
-                ),
-                else_=0,
+            # Finalize by releasing the reservation and charging max cost.
+            charged = await _charge_reservation_rows(
+                session,
+                billing_key_hash=billing_key.hashed_key,
+                key_hash=key.hashed_key,
+                reserved_msats=deducted_max_cost,
+                charge_msats=cost.total_msats,
             )
-
-            finalize_stmt = (
-                update(ApiKey)
-                .where(col(ApiKey.hashed_key) == billing_key.hashed_key)
-                .values(
-                    reserved_balance=safe_reserved,
-                    balance=col(ApiKey.balance) - cost.total_msats,
-                    total_spent=col(ApiKey.total_spent) + cost.total_msats,
-                )
-            )
-            result = await session.exec(finalize_stmt)  # type: ignore[call-overload]
-
-            # Also update total_spent and reserved_balance on the child key if it's different
-            if billing_key.hashed_key != key.hashed_key:
-                child_safe_reserved = case(
-                    (
-                        col(ApiKey.reserved_balance) >= deducted_max_cost,
-                        col(ApiKey.reserved_balance) - deducted_max_cost,
-                    ),
-                    else_=0,
-                )
-                child_stmt = (
-                    update(ApiKey)
-                    .where(col(ApiKey.hashed_key) == key.hashed_key)
-                    .values(
-                        total_spent=col(ApiKey.total_spent) + cost.total_msats,
-                        reserved_balance=child_safe_reserved,
-                    )
-                )
-                await session.exec(child_stmt)  # type: ignore[call-overload]
-
-            await session.commit()
-            if result.rowcount == 0:
+            if charged:
+                await session.commit()
+                await _stop_reservation_heartbeat(reservation.release_id)
+            if not charged:
                 logger.error(
                     "Failed to finalize max-cost payment - retrying reservation release",
                     extra={
-                        "key_hash": key.hashed_key[:8] + "...",
-                        "billing_key_hash": billing_key.hashed_key[:8] + "...",
+                        "key_hash": key_log_hash,
+                        "billing_key_hash": billing_log_hash,
                         "deducted_max_cost": deducted_max_cost,
-                        "current_reserved_balance": billing_key.reserved_balance,
                         "total_cost": cost.total_msats,
                         "model": model,
                     },
                 )
+                cost.charged_msats = 0
                 await release_reservation_only()
             else:
+                cost.charged_msats = cost.total_msats
                 await session.refresh(billing_key)
                 if billing_key.hashed_key != key.hashed_key:
                     await session.refresh(key)
@@ -1314,60 +1488,30 @@ async def adjust_payment_for_tokens(
                         "model": model,
                     },
                 )
-                if billing_key.reserved_balance < deducted_max_cost:
+                if not await _charge_reservation_rows(
+                    session,
+                    billing_key_hash=billing_key.hashed_key,
+                    key_hash=key.hashed_key,
+                    reserved_msats=deducted_max_cost,
+                    charge_msats=total_cost_msats,
+                ):
                     logger.error(
-                        "reserved_balance below deducted_max_cost on exact-cost finalization — clamping to 0",
+                        "Failed to finalize exact-cost payment - releasing reservation",
                         extra={
-                            "key_hash": key.hashed_key[:8] + "...",
-                            "billing_key_hash": billing_key.hashed_key[:8] + "...",
-                            "reserved_balance": billing_key.reserved_balance,
+                            "key_hash": key_log_hash,
+                            "billing_key_hash": billing_log_hash,
                             "deducted_max_cost": deducted_max_cost,
-                            "total_cost_msats": total_cost_msats,
-                            "balance": billing_key.balance,
-                            "total_spent": billing_key.total_spent,
+                            "total_cost": total_cost_msats,
                             "model": model,
                         },
                     )
-
-                exact_safe_reserved = case(
-                    (
-                        col(ApiKey.reserved_balance) >= deducted_max_cost,
-                        col(ApiKey.reserved_balance) - deducted_max_cost,
-                    ),
-                    else_=0,
-                )
-
-                finalize_stmt = (
-                    update(ApiKey)
-                    .where(col(ApiKey.hashed_key) == billing_key.hashed_key)
-                    .values(
-                        reserved_balance=exact_safe_reserved,
-                        balance=col(ApiKey.balance) - total_cost_msats,
-                        total_spent=col(ApiKey.total_spent) + total_cost_msats,
-                    )
-                )
-                await session.exec(finalize_stmt)  # type: ignore[call-overload]
-
-                # Also update total_spent and reserved_balance on the child key if it's different
-                if billing_key.hashed_key != key.hashed_key:
-                    child_exact_safe_reserved = case(
-                        (
-                            col(ApiKey.reserved_balance) >= deducted_max_cost,
-                            col(ApiKey.reserved_balance) - deducted_max_cost,
-                        ),
-                        else_=0,
-                    )
-                    child_stmt = (
-                        update(ApiKey)
-                        .where(col(ApiKey.hashed_key) == key.hashed_key)
-                        .values(
-                            total_spent=col(ApiKey.total_spent) + total_cost_msats,
-                            reserved_balance=child_exact_safe_reserved,
-                        )
-                    )
-                    await session.exec(child_stmt)  # type: ignore[call-overload]
+                    cost.charged_msats = 0
+                    await release_reservation_only()
+                    return cost.dict()
 
                 await session.commit()
+                await _stop_reservation_heartbeat(reservation.release_id)
+                cost.charged_msats = total_cost_msats
                 await session.refresh(billing_key)
                 if billing_key.hashed_key != key.hashed_key:
                     await session.refresh(key)
@@ -1406,50 +1550,70 @@ async def adjust_payment_for_tokens(
                         )
                     ).one()
                     observed_balance = locked_billing_key.balance
-                    actual_charge_msats = min(observed_balance, total_cost_msats)
-                    overrun_safe_reserved = case(
-                        (
-                            col(ApiKey.reserved_balance) >= deducted_max_cost,
-                            col(ApiKey.reserved_balance) - deducted_max_cost,
-                        ),
-                        else_=0,
-                    )
-                    finalize_result = await session.exec(  # type: ignore[call-overload]
-                        update(ApiKey)
-                        .where(col(ApiKey.hashed_key) == billing_key.hashed_key)
-                        .where(col(ApiKey.balance) == observed_balance)
-                        .values(
-                            reserved_balance=overrun_safe_reserved,
-                            balance=col(ApiKey.balance) - actual_charge_msats,
-                            total_spent=col(ApiKey.total_spent) + actual_charge_msats,
+                    observed_reserved = locked_billing_key.reserved_balance
+                    # An overrun may only spend this request's own reservation
+                    # plus funds no other in-flight request has reserved.
+                    # Charging against the raw balance would consume sibling
+                    # reservations and drive the available balance negative.
+                    if observed_reserved < deducted_max_cost:
+                        # Invariant violated — never clamp and charge anyway,
+                        # that would erase sibling reservations. Release only.
+                        logger.error(
+                            "reserved_balance below reservation on overrun finalization — releasing without charge",
+                            extra={
+                                "key_hash": key_log_hash,
+                                "billing_key_hash": billing_log_hash,
+                                "reserved_balance": observed_reserved,
+                                "deducted_max_cost": deducted_max_cost,
+                                "total_cost_msats": total_cost_msats,
+                                "model": model,
+                            },
                         )
-                    )
-                    if finalize_result.rowcount == 1:
+                        await session.rollback()
+                        cost.charged_msats = 0
+                        await release_reservation_only()
+                        return cost.dict()
+                    sibling_reserved = observed_reserved - deducted_max_cost
+                    chargeable_msats = max(0, observed_balance - sibling_reserved)
+                    actual_charge_msats = min(chargeable_msats, total_cost_msats)
+                    if await _charge_reservation_rows(
+                        session,
+                        billing_key_hash=billing_key.hashed_key,
+                        key_hash=key.hashed_key,
+                        reserved_msats=deducted_max_cost,
+                        charge_msats=actual_charge_msats,
+                        extra_billing_guards=(
+                            col(ApiKey.balance) == observed_balance,
+                            col(ApiKey.reserved_balance) == observed_reserved,
+                        ),
+                    ):
                         break
-                    await session.rollback()
                     if not await _claim_reservation_for_charge(reservation, session):
+                        cost.charged_msats = 0
                         return cost.dict()
                 else:
                     await session.rollback()
                     raise RuntimeError("Could not atomically finalize cost overrun")
 
-                if billing_key.hashed_key != key.hashed_key:
-                    child_stmt = (
-                        update(ApiKey)
-                        .where(col(ApiKey.hashed_key) == key.hashed_key)
-                        .values(
-                            reserved_balance=overrun_safe_reserved,
-                            total_spent=col(ApiKey.total_spent) + actual_charge_msats,
-                        )
-                    )
-                    await session.exec(child_stmt)  # type: ignore[call-overload]
-
                 await session.commit()
+                await _stop_reservation_heartbeat(reservation.release_id)
 
                 await session.refresh(billing_key)
                 if billing_key.hashed_key != key.hashed_key:
                     await session.refresh(key)
-                cost.total_msats = actual_charge_msats
+                cost.charged_msats = actual_charge_msats
+                if actual_charge_msats < total_cost_msats:
+                    logger.warning(
+                        "Cost overrun exceeded chargeable funds — shortfall written off",
+                        extra={
+                            "key_hash": key.hashed_key[:8] + "...",
+                            "billing_key_hash": billing_key.hashed_key[:8] + "...",
+                            "actual_cost_msats": total_cost_msats,
+                            "charged_msats": actual_charge_msats,
+                            "shortfall_msats": total_cost_msats - actual_charge_msats,
+                            "model": model,
+                        },
+                    )
                 logger.info(
                     "Finalized payment with additional charge",
                     extra={
@@ -1492,77 +1656,33 @@ async def adjust_payment_for_tokens(
                     },
                 )
 
-                if billing_key.reserved_balance < deducted_max_cost:
-                    logger.error(
-                        "reserved_balance below deducted_max_cost on refund finalization — clamping to 0",
-                        extra={
-                            "key_hash": key.hashed_key[:8] + "...",
-                            "billing_key_hash": billing_key.hashed_key[:8] + "...",
-                            "reserved_balance": billing_key.reserved_balance,
-                            "deducted_max_cost": deducted_max_cost,
-                            "total_cost_msats": total_cost_msats,
-                            "refund_amount": refund,
-                            "balance": billing_key.balance,
-                            "total_spent": billing_key.total_spent,
-                            "model": model,
-                        },
-                    )
-
-                refund_safe_reserved = case(
-                    (
-                        col(ApiKey.reserved_balance) >= deducted_max_cost,
-                        col(ApiKey.reserved_balance) - deducted_max_cost,
-                    ),
-                    else_=0,
+                charged = await _charge_reservation_rows(
+                    session,
+                    billing_key_hash=billing_key.hashed_key,
+                    key_hash=key.hashed_key,
+                    reserved_msats=deducted_max_cost,
+                    charge_msats=total_cost_msats,
                 )
+                if charged:
+                    await session.commit()
+                    await _stop_reservation_heartbeat(reservation.release_id)
 
-                refund_stmt = (
-                    update(ApiKey)
-                    .where(col(ApiKey.hashed_key) == billing_key.hashed_key)
-                    .values(
-                        reserved_balance=refund_safe_reserved,
-                        balance=col(ApiKey.balance) - total_cost_msats,
-                        total_spent=col(ApiKey.total_spent) + total_cost_msats,
-                    )
-                )
-                result = await session.exec(refund_stmt)  # type: ignore[call-overload]
-
-                # Also update total_spent and reserved_balance on the child key if it's different
-                if billing_key.hashed_key != key.hashed_key:
-                    child_refund_safe_reserved = case(
-                        (
-                            col(ApiKey.reserved_balance) >= deducted_max_cost,
-                            col(ApiKey.reserved_balance) - deducted_max_cost,
-                        ),
-                        else_=0,
-                    )
-                    child_stmt = (
-                        update(ApiKey)
-                        .where(col(ApiKey.hashed_key) == key.hashed_key)
-                        .values(
-                            total_spent=col(ApiKey.total_spent) + total_cost_msats,
-                            reserved_balance=child_refund_safe_reserved,
-                        )
-                    )
-                    await session.exec(child_stmt)  # type: ignore[call-overload]
-
-                await session.commit()
-
-                if result.rowcount == 0:
+                if not charged:
                     logger.error(
                         "Failed to finalize payment - releasing reservation",
                         extra={
-                            "key_hash": key.hashed_key[:8] + "...",
-                            "billing_key_hash": billing_key.hashed_key[:8] + "...",
+                            "key_hash": key_log_hash,
+                            "billing_key_hash": billing_log_hash,
                             "deducted_max_cost": deducted_max_cost,
-                            "current_reserved_balance": billing_key.reserved_balance,
                             "total_cost": total_cost_msats,
                             "model": model,
                         },
                     )
+                    cost.charged_msats = 0
                     await release_reservation_only()
                 else:
                     cost.total_msats = total_cost_msats
+                    cost.charged_msats = total_cost_msats
                     await session.refresh(billing_key)
                     if billing_key.hashed_key != key.hashed_key:
                         await session.refresh(key)
diff --git a/routstr/core/admin.py b/routstr/core/admin.py
index 5f6c8604..985f9c46 100644
--- a/routstr/core/admin.py
+++ b/routstr/core/admin.py
@@ -69,7 +69,9 @@ async def require_admin_api(request: Request) -> None:
     async with create_session() as session:
         result = await session.exec(select(CliToken).where(CliToken.token == token))
         cli_token = result.first()
-        if cli_token and (cli_token.expires_at is None or cli_token.expires_at > now_ts):
+        if cli_token and (
+            cli_token.expires_at is None or cli_token.expires_at > now_ts
+        ):
             cli_token.last_used_at = now_ts
             session.add(cli_token)
             await session.commit()
@@ -107,7 +109,7 @@ async def get_temporary_balances_api(
         # Aggregate totals across the whole (search-filtered) set, not just the
         # current page. Balance counts only parent (non-child) keys to avoid
         # double-counting, since child keys draw from their parent's balance.
-        totals_result = await session.exec(
+        balance_totals_result = await session.exec(
             select(
                 func.coalesce(
                     func.sum(
@@ -118,11 +120,44 @@ async def get_temporary_balances_api(
                     ),
                     0,
                 ),
+                func.coalesce(
+                    func.sum(
+                        case(
+                            (
+                                col(ApiKey.parent_key_hash).is_(None),
+                                ApiKey.reserved_balance,
+                            ),
+                            else_=0,
+                        )
+                    ),
+                    0,
+                ),
+                func.coalesce(
+                    func.sum(
+                        case(
+                            (
+                                col(ApiKey.parent_key_hash).is_(None),
+                                col(ApiKey.balance) - col(ApiKey.reserved_balance),
+                            ),
+                            else_=0,
+                        )
+                    ),
+                    0,
+                ),
+            ).where(*filters)
+        )
+        (
+            total_balance,
+            total_reserved_balance,
+            total_available_balance,
+        ) = balance_totals_result.one()
+        usage_totals_result = await session.exec(
+            select(
                 func.coalesce(func.sum(ApiKey.total_spent), 0),
                 func.coalesce(func.sum(ApiKey.total_requests), 0),
             ).where(*filters)
         )
-        total_balance, total_spent, total_requests = totals_result.one()
+        total_spent, total_requests = usage_totals_result.one()
 
         # Latest created first; keys with no created_at (legacy rows) sort last.
         # Use an explicit CASE rather than relying on dialect NULL-ordering so
@@ -143,6 +178,10 @@ async def get_temporary_balances_api(
             {
                 "hashed_key": key.hashed_key,
                 "balance": key.balance,
+                "reserved_balance": key.reserved_balance,
+                "available_balance": (
+                    key.total_balance if key.parent_key_hash is None else None
+                ),
                 "total_spent": key.total_spent,
                 "total_requests": key.total_requests,
                 "refund_address": key.refund_address,
@@ -158,6 +197,8 @@ async def get_temporary_balances_api(
         "total": total,
         "totals": {
             "total_balance": total_balance,
+            "total_reserved_balance": total_reserved_balance,
+            "total_available_balance": total_available_balance,
             "total_spent": total_spent,
             "total_requests": total_requests,
         },
@@ -256,16 +297,12 @@ async def update_password(request: Request, password_update: PasswordUpdate) ->
         secret = await get_secret(session)
 
         if not secret.admin_password_hash:
-            raise HTTPException(
-                status_code=500, detail="Admin password not configured"
-            )
+            raise HTTPException(status_code=500, detail="Admin password not configured")
 
         if not vault.verify_password(
             password_update.current_password, secret.admin_password_hash
         ):
-            raise HTTPException(
-                status_code=401, detail="Current password is incorrect"
-            )
+            raise HTTPException(status_code=401, detail="Current password is incorrect")
 
         # Validate new password
         new_password = password_update.new_password.strip()
@@ -883,9 +920,7 @@ async def _active_ppq_claim_in_session(session: AsyncSession, provider_id: int)
     return claim is not None and not claim.collected and not claim.swept
 
 
-def _require_valid_ppq_auto_topup(
-    provider_type: str, settings: dict | None
-) -> None:
+def _require_valid_ppq_auto_topup(provider_type: str, settings: dict | None) -> None:
     """Reject PPQ auto top-up settings the worker would later refuse."""
     if provider_type != "ppqai":
         return
@@ -1017,9 +1052,7 @@ async def create_upstream_provider(
         else:
             slug = await allocate_unique_provider_slug(session, payload.provider_type)
 
-        _require_valid_ppq_auto_topup(
-            payload.provider_type, payload.provider_settings
-        )
+        _require_valid_ppq_auto_topup(payload.provider_type, payload.provider_settings)
 
         provider = UpstreamProviderRow(
             slug=slug,
@@ -1078,9 +1111,7 @@ async def update_upstream_provider_by_slug(
     lookup = _validate_slug(payload.slug)
     async with create_session() as session:
         result = await session.exec(
-            select(UpstreamProviderRow).where(
-                UpstreamProviderRow.slug == lookup
-            )
+            select(UpstreamProviderRow).where(UpstreamProviderRow.slug == lookup)
         )
         provider = result.first()
         if not provider:
@@ -1910,9 +1941,7 @@ async def get_transactions_api(
         }
 
 
-@admin_router.get(
-    "/api/lightning-invoices", dependencies=[Depends(require_admin_api)]
-)
+@admin_router.get("/api/lightning-invoices", dependencies=[Depends(require_admin_api)])
 async def get_lightning_invoices_api(
     status: str | None = None,
     purpose: str | None = None,
diff --git a/routstr/core/db.py b/routstr/core/db.py
index f31691a1..2ab5ef25 100644
--- a/routstr/core/db.py
+++ b/routstr/core/db.py
@@ -171,6 +171,55 @@ async def reset_all_reserved_balances(session: AsyncSession) -> None:
     logger.info("Reset reserved balances on startup")
 
 
+async def _transition_stale_reservation(
+    session: AsyncSession, reservation_id: str, cutoff: int
+) -> bool:
+    """Mark one reservation released iff its lease is still older than cutoff.
+
+    ``created_at`` doubles as the heartbeat lease timestamp, so the guard must
+    be part of this update: a reservation renewed between the sweeper's select
+    and this transition is in flight and must survive.
+    """
+    transition = await session.exec(  # type: ignore[call-overload]
+        update(ReservationRelease)
+        .where(col(ReservationRelease.id) == reservation_id)
+        .where(col(ReservationRelease.status) == "active")
+        .where(col(ReservationRelease.created_at) < cutoff)
+        .values(status="released")
+    )
+    return bool(transition.rowcount == 1)
+
+
+async def _release_legacy_aggregate(
+    session: AsyncSession,
+    key_hash: str,
+    observed_reserved: int,
+    observed_reserved_at: int | None,
+) -> bool:
+    """Zero one legacy aggregate reservation iff it is exactly as observed.
+
+    A new reservation committing between the sweeper's read and this update
+    changes ``reserved_balance``/``reserved_at`` in the same transaction that
+    creates its durable row, so this compare-and-swap fails instead of erasing
+    the newcomer's reserved funds.
+    """
+    if observed_reserved <= 0:
+        return False
+    reserved_at_guard = (
+        col(ApiKey.reserved_at).is_(None)
+        if observed_reserved_at is None
+        else col(ApiKey.reserved_at) == observed_reserved_at
+    )
+    result = await session.exec(  # type: ignore[call-overload]
+        update(ApiKey)
+        .where(col(ApiKey.hashed_key) == key_hash)
+        .where(col(ApiKey.reserved_balance) == observed_reserved)
+        .where(reserved_at_guard)
+        .values(reserved_balance=0, reserved_at=None)
+    )
+    return bool(result.rowcount == 1)
+
+
 async def release_stale_reservations(
     session: AsyncSession,
     max_age_seconds: int,
@@ -191,25 +240,22 @@ async def release_stale_reservations(
                 col(ReservationRelease.billing_key_hash) == key_hash,
             )
         )
-    reservations = (await session.exec(query)).all()
+    # Capture primitives: a repair rollback below would expire ORM instances.
+    reservation_rows = [
+        (r.id, r.key_hash, r.billing_key_hash, r.reserved_msats)
+        for r in (await session.exec(query)).all()
+    ]
     released = 0
 
-    for reservation in reservations:
-        transition = await session.exec(  # type: ignore[call-overload]
-            update(ReservationRelease)
-            .where(col(ReservationRelease.id) == reservation.id)
-            .where(col(ReservationRelease.status) == "active")
-            .values(status="released")
-        )
-        if transition.rowcount != 1:
+    for res_id, res_key_hash, res_billing_hash, res_msats in reservation_rows:
+        if not await _transition_stale_reservation(session, res_id, cutoff):
             continue
 
         values = {
-            "reserved_balance": col(ApiKey.reserved_balance)
-            - reservation.reserved_msats,
+            "reserved_balance": col(ApiKey.reserved_balance) - res_msats,
             "reserved_at": case(
                 (
-                    col(ApiKey.reserved_balance) - reservation.reserved_msats > 0,
+                    col(ApiKey.reserved_balance) - res_msats > 0,
                     col(ApiKey.reserved_at),
                 ),
                 else_=None,
@@ -217,24 +263,42 @@ async def release_stale_reservations(
         }
         parent_result = await session.exec(  # type: ignore[call-overload]
             update(ApiKey)
-            .where(col(ApiKey.hashed_key) == reservation.billing_key_hash)
-            .where(col(ApiKey.reserved_balance) >= reservation.reserved_msats)
+            .where(col(ApiKey.hashed_key) == res_billing_hash)
+            .where(col(ApiKey.reserved_balance) >= res_msats)
             .values(**values)
         )
-        if parent_result.rowcount != 1:
-            await session.rollback()
-            return 0
-
-        if reservation.billing_key_hash != reservation.key_hash:
+        aggregates_ok = parent_result.rowcount == 1
+        if aggregates_ok and res_billing_hash != res_key_hash:
             child_result = await session.exec(  # type: ignore[call-overload]
                 update(ApiKey)
-                .where(col(ApiKey.hashed_key) == reservation.key_hash)
-                .where(col(ApiKey.reserved_balance) >= reservation.reserved_msats)
+                .where(col(ApiKey.hashed_key) == res_key_hash)
+                .where(col(ApiKey.reserved_balance) >= res_msats)
                 .values(**values)
             )
-            if child_result.rowcount != 1:
-                await session.rollback()
-                return 0
+            aggregates_ok = child_result.rowcount == 1
+
+        if not aggregates_ok:
+            # The aggregates no longer hold this reservation's msats — the
+            # durable row is corrupt. Repair by terminalizing it WITHOUT
+            # subtracting uncertain aggregates (legacy cleanup below reconciles
+            # any stale remainder) and keep sweeping the rest of the batch:
+            # one corrupt row must not poison all stale cleanup.
+            await session.rollback()
+            if await _transition_stale_reservation(session, res_id, cutoff):
+                await session.commit()
+                released += 1
+                logger.error(
+                    "Released corrupt stale reservation without aggregate subtraction",
+                    extra={
+                        "reservation_id": res_id,
+                        "billing_key_hash": res_billing_hash[:8] + "...",
+                        "reserved_msats": res_msats,
+                    },
+                )
+            continue
+        # Commit each release on its own so a later corrupt record's rollback
+        # cannot discard the healthy releases already processed in this batch.
+        await session.commit()
         released += 1
 
     # Rolling upgrades can leave aggregate reservations created before durable
@@ -256,6 +320,8 @@ async def release_stale_reservations(
         )
 
     for legacy_key in (await session.exec(legacy_query)).all():
+        observed_reserved = legacy_key.reserved_balance
+        observed_reserved_at = legacy_key.reserved_at
         active_owner = (
             await session.exec(
                 select(ReservationRelease.id)
@@ -272,10 +338,10 @@ async def release_stale_reservations(
         ).first()
         if active_owner is not None:
             continue
-        legacy_key.reserved_balance = 0
-        legacy_key.reserved_at = None
-        session.add(legacy_key)
-        released += 1
+        if await _release_legacy_aggregate(
+            session, legacy_key.hashed_key, observed_reserved, observed_reserved_at
+        ):
+            released += 1
 
     await session.commit()
     if released:
diff --git a/routstr/payment/cost_calculation.py b/routstr/payment/cost_calculation.py
index 0fb305cb..7dbab415 100644
--- a/routstr/payment/cost_calculation.py
+++ b/routstr/payment/cost_calculation.py
@@ -34,6 +34,8 @@ class CostData(BaseModel):
     cache_creation_input_tokens: int = 0
     cache_read_msats: int = 0
     cache_creation_msats: int = 0
+    # Actual debit after finalization; None means settlement has not run yet.
+    charged_msats: int | None = None
 
 
 class MaxCostData(CostData):
@@ -247,9 +249,7 @@ async def calculate_cost(
             "Token counts %s in the upstream response but cannot be "
             "priced; the request will appear in dashboards with the "
             "raw counts and a fixed max-cost charge.",
-            "are present"
-            if (input_tokens > 0 or output_tokens > 0)
-            else "are zero",
+            "are present" if (input_tokens > 0 or output_tokens > 0) else "are zero",
             extra={
                 "base_cost_msats": max_cost,
                 "model": response_data.get("model", "unknown"),
@@ -326,9 +326,7 @@ def _resolve_usd_cost(usage_data: dict, response_data: dict) -> float:
         # actually deducts from the balance.  For non-BYOK providers (e.g.
         # OpenRouter) usage.cost already equals upstream_inference_cost, so we
         # fall through to the normal ``cost`` lookup below.
-        upstream_cost = _coerce_usd(
-            cost_details.get("upstream_inference_cost")
-        )
+        upstream_cost = _coerce_usd(cost_details.get("upstream_inference_cost"))
         if upstream_cost > 0 and usage_data.get("is_byok"):
             byok_fee = _coerce_usd(usage_data.get("cost"))
             return upstream_cost + byok_fee
@@ -359,8 +357,7 @@ def _get_pricing_rates(
     ``None`` means configured fixed pricing should be used by the caller.
     """
     if settings.fixed_pricing and (
-        settings.fixed_per_1k_input_tokens
-        or settings.fixed_per_1k_output_tokens
+        settings.fixed_per_1k_input_tokens or settings.fixed_per_1k_output_tokens
     ):
         return None
 
@@ -416,12 +413,8 @@ def _get_pricing_rates(
         usd_per_sat = sats_usd_price()
         mspp_1k = input_usd * provider_fee * 1_000_000.0 / usd_per_sat
         mspc_1k = output_usd * provider_fee * 1_000_000.0 / usd_per_sat
-        cache_read_usd = _coerce_usd(
-            pricing.get("cache_read_input_token_cost")
-        )
-        cache_write_usd = _coerce_usd(
-            pricing.get("cache_creation_input_token_cost")
-        )
+        cache_read_usd = _coerce_usd(pricing.get("cache_read_input_token_cost"))
+        cache_write_usd = _coerce_usd(pricing.get("cache_creation_input_token_cost"))
         mscr_1k = (
             cache_read_usd * provider_fee * 1_000_000.0 / usd_per_sat
             if cache_read_usd > 0
@@ -525,9 +518,7 @@ def _calculate_from_usd_cost(
         regular_weight = input_tokens * input_rate
         cache_read_weight = cache_read_tokens * cache_read_rate
         cache_creation_weight = cache_creation_tokens * cache_creation_rate
-        total_input_weight = (
-            regular_weight + cache_read_weight + cache_creation_weight
-        )
+        total_input_weight = regular_weight + cache_read_weight + cache_creation_weight
         if total_input_weight > 0:
             cache_read_msats = int(
                 round(
diff --git a/routstr/upstream/base.py b/routstr/upstream/base.py
index bc9fd547..61f2696f 100644
--- a/routstr/upstream/base.py
+++ b/routstr/upstream/base.py
@@ -83,6 +83,24 @@ def _cost_field(
     return value if isinstance(value, (int, float)) else default
 
 
+def _settled_cost_msats(cost_data: CostMetadata) -> int:
+    charged = _cost_field(cost_data, "charged_msats", -1)
+    if charged >= 0:
+        return int(charged)
+    return int(_cost_field(cost_data, "total_msats"))
+
+
+def _published_cost(cost_data: CostMetadata) -> dict[str, Any]:
+    cost = dict(cost_data) if isinstance(cost_data, dict) else cost_data.dict()
+    computed_msats = int(_cost_field(cost_data, "total_msats"))
+    settled_msats = _settled_cost_msats(cost_data)
+    if computed_msats != settled_msats:
+        cost["computed_msats"] = computed_msats
+    cost["total_msats"] = settled_msats
+    cost["charged_msats"] = settled_msats
+    return cost
+
+
 def _inject_cost_response_headers(
     headers: dict[str, str], cost_data: CostMetadata
 ) -> None:
@@ -93,9 +111,11 @@ def _inject_cost_response_headers(
     usage tracking entry — without them, x-cashu requests show 0.0 for all
     sat cost fields.
     """
-    headers["X-Routstr-Cost-Msats"] = str(
-        int(_cost_field(cost_data, "total_msats"))
-    )
+    settled_msats = _settled_cost_msats(cost_data)
+    computed_msats = int(_cost_field(cost_data, "total_msats"))
+    headers["X-Routstr-Cost-Msats"] = str(settled_msats)
+    if computed_msats != settled_msats:
+        headers["X-Routstr-Computed-Cost-Msats"] = str(computed_msats)
     headers["X-Routstr-Input-Cost-Msats"] = str(
         int(_cost_field(cost_data, "input_msats"))
     )
@@ -122,11 +142,14 @@ def _inject_cost_into_usage(response_json: dict, cost_data: CostMetadata) -> Non
     # data always overwrites any upstream-provided cost values. Using
     # setdefault would silently keep stale upstream values and drop our
     # calculated msats breakdown.
+    computed_msats = int(_cost_field(cost_data, "total_msats"))
+    settled_msats = _settled_cost_msats(cost_data)
     cost_obj: dict[str, int | float] = {
         "base_msats": int(_cost_field(cost_data, "base_msats")),
         "input_msats": int(_cost_field(cost_data, "input_msats")),
         "output_msats": int(_cost_field(cost_data, "output_msats")),
-        "total_msats": int(_cost_field(cost_data, "total_msats")),
+        "total_msats": settled_msats,
+        "charged_msats": settled_msats,
         "cache_read_input_tokens": int(
             _cost_field(cost_data, "cache_read_input_tokens")
         ),
@@ -134,15 +157,15 @@ def _inject_cost_into_usage(response_json: dict, cost_data: CostMetadata) -> Non
             _cost_field(cost_data, "cache_creation_input_tokens")
         ),
         "cache_read_msats": int(_cost_field(cost_data, "cache_read_msats")),
-        "cache_creation_msats": int(
-            _cost_field(cost_data, "cache_creation_msats")
-        ),
+        "cache_creation_msats": int(_cost_field(cost_data, "cache_creation_msats")),
     }
+    if computed_msats != settled_msats:
+        cost_obj["computed_msats"] = computed_msats
     total_usd = float(_cost_field(cost_data, "total_usd", 0.0))
     if total_usd:
         cost_obj["total_usd"] = total_usd
     usage["cost"] = cost_obj
-    usage["cost_sats"] = int(_cost_field(cost_data, "total_msats")) // 1000
+    usage["cost_sats"] = settled_msats // 1000
 
 
 def _is_json_content_type(content_type: str | None) -> bool:
@@ -349,14 +372,8 @@ class BaseUpstreamProvider:
     ) -> None:
         """Unifies the injection of cost and usage metadata across all completion types."""
         self._apply_provider_field(response_json)
-        if isinstance(cost_data, dict):
-            total_msats = cost_data.get("total_msats", 0)
-            cost_dict = cost_data
-        else:
-            total_msats = cost_data.total_msats
-            cost_dict = cost_data.dict()
-
-        sats_cost = total_msats // 1000
+        cost_dict = _published_cost(cost_data)
+        sats_cost = cost_dict["total_msats"] // 1000
 
         # Inject the shared SDK cost contract into every usage shape.
         if isinstance(response_json.get("usage"), dict):
@@ -370,6 +387,14 @@ class BaseUpstreamProvider:
             message["usage"]["remaining_balance_msats"] = key.balance
             self._fold_cache_into_input_tokens(message["usage"])
 
+        nested_response = response_json.get("response")
+        if isinstance(nested_response, dict) and isinstance(
+            nested_response.get("usage"), dict
+        ):
+            _inject_cost_into_usage(nested_response, cost_data)
+            nested_response["usage"]["remaining_balance_msats"] = key.balance
+            self._fold_cache_into_input_tokens(nested_response["usage"])
+
         # Unified Routstr metadata
         response_json["metadata"] = response_json.get("metadata", {})
         response_json["metadata"]["routstr"] = {
@@ -1307,18 +1332,12 @@ class BaseUpstreamProvider:
                 )
                 self._fold_cache_into_input_tokens(response_json["usage"])
 
-            # Keep detailed cost
+            published_cost = _published_cost(cost_data)
+            published_cost["sats_cost"] = published_cost["total_msats"] // 1000
+            published_cost["remaining_balance_msats"] = remaining_balance_msats
             response_json["metadata"] = response_json.get("metadata", {})
-            response_json["metadata"]["routstr"] = {"cost": cost_data}
-            response_json["metadata"]["routstr"]["cost"]["sats_cost"] = (
-                cost_data.get("total_msats", 0) // 1000
-            )
-            response_json["metadata"]["routstr"]["cost"]["remaining_balance_msats"] = (
-                remaining_balance_msats
-            )
-            response_json["cost"] = cost_data
-            response_json["cost"]["sats_cost"] = cost_data.get("total_msats", 0) // 1000
-            response_json["cost"]["remaining_balance_msats"] = remaining_balance_msats
+            response_json["metadata"]["routstr"] = {"cost": published_cost.copy()}
+            response_json["cost"] = published_cost
 
             logger.debug(
                 "Payment adjustment completed for non-streaming",
@@ -1609,24 +1628,6 @@ class BaseUpstreamProvider:
                                 },
                             }
 
-                        remaining_balance_msats = fresh_key.balance
-                        sats_cost = cost_data.get("total_msats", 0) // 1000
-
-                        if (
-                            "response" in usage_chunk_data
-                            and isinstance(usage_chunk_data["response"], dict)
-                            and "usage" in usage_chunk_data["response"]
-                        ):
-                            usage_chunk_data["response"]["usage"]["cost"] = (
-                                cost_data.get("total_usd", 0.0)
-                            )
-                            usage_chunk_data["response"]["usage"]["cost_sats"] = (
-                                sats_cost
-                            )
-                            usage_chunk_data["response"]["usage"][
-                                "remaining_balance_msats"
-                            ] = remaining_balance_msats
-
                         try:
                             self.inject_cost_metadata(
                                 usage_chunk_data, cost_data, fresh_key
@@ -1742,18 +1743,12 @@ class BaseUpstreamProvider:
                 )
                 self._fold_cache_into_input_tokens(response_json["usage"])
 
-            # Keep detailed cost
+            published_cost = _published_cost(cost_data)
+            published_cost["sats_cost"] = published_cost["total_msats"] // 1000
+            published_cost["remaining_balance_msats"] = remaining_balance_msats
             response_json["metadata"] = response_json.get("metadata", {})
-            response_json["metadata"]["routstr"] = {"cost": cost_data}
-            response_json["metadata"]["routstr"]["cost"]["sats_cost"] = (
-                cost_data.get("total_msats", 0) // 1000
-            )
-            response_json["metadata"]["routstr"]["cost"]["remaining_balance_msats"] = (
-                remaining_balance_msats
-            )
-            response_json["cost"] = cost_data
-            response_json["cost"]["sats_cost"] = cost_data.get("total_msats", 0) // 1000
-            response_json["cost"]["remaining_balance_msats"] = remaining_balance_msats
+            response_json["metadata"]["routstr"] = {"cost": published_cost.copy()}
+            response_json["cost"] = published_cost
 
             logger.debug(
                 "Payment adjustment completed for non-streaming Responses API",
@@ -2747,9 +2742,7 @@ class BaseUpstreamProvider:
                     event_type = str(event.get("type") or "")
                     prefix = f"event: {event_type}\n" if event_type else ""
                     buffered[index] = annotated._replace(
-                        sse_bytes=(
-                            f"{prefix}data: {json.dumps(event)}\n\n".encode()
-                        )
+                        sse_bytes=(f"{prefix}data: {json.dumps(event)}\n\n".encode())
                     )
 
         async def replay() -> AsyncGenerator[bytes, None]:
@@ -3822,11 +3815,7 @@ class BaseUpstreamProvider:
                     if "provider" not in data_json:
                         self._apply_provider_field(data_json)
                         changed = True
-                    if (
-                        cost_data
-                        and "usage" in data_json
-                        and data_json["usage"]
-                    ):
+                    if cost_data and "usage" in data_json and data_json["usage"]:
                         _inject_cost_into_usage(data_json, cost_data)
                         changed = True
                     if changed:
@@ -4811,11 +4800,7 @@ class BaseUpstreamProvider:
                     if "provider" not in data_json:
                         self._apply_provider_field(data_json)
                         changed = True
-                    if (
-                        cost_data
-                        and "usage" in data_json
-                        and data_json["usage"]
-                    ):
+                    if cost_data and "usage" in data_json and data_json["usage"]:
                         _inject_cost_into_usage(data_json, cost_data)
                         changed = True
                     if changed:
diff --git a/routstr/upstream/ehbp.py b/routstr/upstream/ehbp.py
index c70a3b68..55541d22 100644
--- a/routstr/upstream/ehbp.py
+++ b/routstr/upstream/ehbp.py
@@ -10,17 +10,18 @@ from urllib.parse import urlsplit, urlunsplit
 
 from fastapi import Request
 from fastapi.responses import Response, StreamingResponse
-from sqlalchemy import case
-from sqlmodel import col, update
 
 from ..auth import (
     ROUTSTR_FEE_PERCENT,
     ReservationSnapshot,
+    _charge_reservation_rows,
     _claim_reservation_for_charge,
+    _stop_reservation_heartbeat,
     _validate_reservation_snapshot,
     get_billing_key,
     get_reservation_snapshot,
     payments_logger,
+    release_reservation,
 )
 from ..core import get_logger
 from ..core.db import (
@@ -191,7 +192,9 @@ def _resolve_ehbp_target_url(
     otherwise the header is ignored so callers cannot redirect other providers
     or leak upstream API keys.
     """
-    override_header = profile.client_target_url_header if profile else _ENCLAVE_URL_HEADER
+    override_header = (
+        profile.client_target_url_header if profile else _ENCLAVE_URL_HEADER
+    )
     if not override_header:
         return target_url
     enclave_url = _get_header_case_insensitive(headers, override_header)
@@ -295,9 +298,7 @@ def _build_cost_info(
     return result
 
 
-def _inject_cost_response_headers(
-    headers: dict[str, str], cost_info: dict
-) -> None:
+def _inject_cost_response_headers(headers: dict[str, str], cost_info: dict) -> None:
     """Add per-request cost headers to an EHBP response.
 
     Since EHBP response bodies are opaque encrypted blobs, cost cannot be
@@ -305,6 +306,8 @@ def _inject_cost_response_headers(
     the client/Tinfoil SDK can read without decrypting.
     """
     headers["X-Routstr-Cost-Msats"] = str(cost_info["total_msats"])
+    if "computed_msats" in cost_info:
+        headers["X-Routstr-Computed-Cost-Msats"] = str(cost_info["computed_msats"])
     headers["X-Routstr-Input-Cost-Msats"] = str(cost_info["input_msats"])
     headers["X-Routstr-Output-Cost-Msats"] = str(cost_info["output_msats"])
 
@@ -375,9 +378,7 @@ async def _compute_ehbp_actual_cost(
             resolved_upstream_model = (
                 actual_model_obj.forwarded_model_id or actual_model_obj.id
             )
-            resolved_identity = _normalize_upstream_model_id(
-                resolved_upstream_model
-            )
+            resolved_identity = _normalize_upstream_model_id(resolved_upstream_model)
             if resolved_identity != expected_identity:
                 logger.info(
                     "EHBP served model differs from requested, using actual "
@@ -500,6 +501,18 @@ class EHBPForwardingTarget:
     profile: ConfidentialInferenceProfile | None = None
 
 
+async def _release_failed_ehbp_charge(
+    reservation: ReservationSnapshot, session: AsyncSession
+) -> None:
+    if await release_reservation(reservation, session, reservation.reserved_msats):
+        return
+    await _stop_reservation_heartbeat(reservation.release_id)
+    logger.critical(
+        "Failed to release EHBP reservation after rejected charge",
+        extra={"reservation_id": reservation.release_id},
+    )
+
+
 async def finalize_ehbp_actual_cost_payment(
     key: ApiKey,
     session: AsyncSession,
@@ -507,61 +520,29 @@ async def finalize_ehbp_actual_cost_payment(
     model_id: str,
     cost_info: dict,
     reservation_snapshot: ReservationSnapshot | None = None,
-) -> None:
+) -> int:
     """Finalize an EHBP bearer request using clamped provider usage metrics."""
     reservation = reservation_snapshot or await get_reservation_snapshot(key, session)
     await _validate_reservation_snapshot(key, reservation, session)
     if not await _claim_reservation_for_charge(reservation, session):
-        return
+        return 0
     reserved_cost_for_model = reservation.reserved_msats
     billing_key = await get_billing_key(key, session)
     key_hash = key.hashed_key
     billing_key_hash = billing_key.hashed_key
-    total_cost_msats = max(0, int(cost_info.get("total_msats", reserved_cost_for_model)))
+    total_cost_msats = max(
+        0, int(cost_info.get("total_msats", reserved_cost_for_model))
+    )
     now = int(time.time())
 
-    safe_reserved = case(
-        (
-            col(ApiKey.reserved_balance) >= reserved_cost_for_model,
-            col(ApiKey.reserved_balance) - reserved_cost_for_model,
-        ),
-        else_=0,
+    charged = await _charge_reservation_rows(
+        session,
+        billing_key_hash=billing_key_hash,
+        key_hash=key_hash,
+        reserved_msats=reserved_cost_for_model,
+        charge_msats=total_cost_msats,
     )
-    cleared_reserved_at = case(
-        (
-            col(ApiKey.reserved_balance) - reserved_cost_for_model > 0,
-            col(ApiKey.reserved_at),
-        ),
-        else_=None,
-    )
-
-    stmt = (
-        update(ApiKey)
-        .where(col(ApiKey.hashed_key) == billing_key.hashed_key)
-        .values(
-            reserved_balance=safe_reserved,
-            reserved_at=cleared_reserved_at,
-            balance=col(ApiKey.balance) - total_cost_msats,
-            total_spent=col(ApiKey.total_spent) + total_cost_msats,
-        )
-    )
-    result = await session.exec(stmt)  # type: ignore[call-overload]
-
-    child_result = None
-    if billing_key.hashed_key != key.hashed_key:
-        child_stmt = (
-            update(ApiKey)
-            .where(col(ApiKey.hashed_key) == key.hashed_key)
-            .values(
-                reserved_balance=safe_reserved,
-                reserved_at=cleared_reserved_at,
-                total_spent=col(ApiKey.total_spent) + total_cost_msats,
-            )
-        )
-        child_result = await session.exec(child_stmt)  # type: ignore[call-overload]
-
-    if result.rowcount == 0 or (child_result is not None and child_result.rowcount == 0):
-        await session.rollback()
+    if not charged:
         logger.error(
             "Failed to finalize EHBP usage-based payment",
             extra={
@@ -570,13 +551,13 @@ async def finalize_ehbp_actual_cost_payment(
                 "model": model_id,
                 "reserved_cost_for_model": reserved_cost_for_model,
                 "total_cost_msats": total_cost_msats,
-                "parent_rowcount": result.rowcount,
-                "child_rowcount": getattr(child_result, "rowcount", None),
             },
         )
-        return
+        await _release_failed_ehbp_charge(reservation, session)
+        return 0
 
     await session.commit()
+    await _stop_reservation_heartbeat(reservation.release_id)
     await session.refresh(billing_key)
     if billing_key.hashed_key != key.hashed_key:
         await session.refresh(key)
@@ -609,6 +590,7 @@ async def finalize_ehbp_actual_cost_payment(
             "finalized_at": now,
         },
     )
+    return total_cost_msats
 
 
 async def finalize_ehbp_max_cost_payment(
@@ -617,7 +599,7 @@ async def finalize_ehbp_max_cost_payment(
     max_cost_for_model: int,
     model_id: str,
     reservation_snapshot: ReservationSnapshot | None = None,
-) -> None:
+) -> int:
     """Finalize an EHBP bearer request by charging the reserved max cost.
 
     EHBP responses are encrypted, so Routstr cannot inspect token usage. Unlike
@@ -627,7 +609,7 @@ async def finalize_ehbp_max_cost_payment(
     reservation = reservation_snapshot or await get_reservation_snapshot(key, session)
     await _validate_reservation_snapshot(key, reservation, session)
     if not await _claim_reservation_for_charge(reservation, session):
-        return
+        return 0
     max_cost_for_model = reservation.reserved_msats
     billing_key = await get_billing_key(key, session)
     key_hash = key.hashed_key
@@ -635,63 +617,14 @@ async def finalize_ehbp_max_cost_payment(
     total_cost_msats = max(0, int(max_cost_for_model))
     now = int(time.time())
 
-    cleared_reserved_at = case(
-        (
-            col(ApiKey.reserved_balance) - max_cost_for_model > 0,
-            col(ApiKey.reserved_at),
-        ),
-        else_=None,
+    charged = await _charge_reservation_rows(
+        session,
+        billing_key_hash=billing_key_hash,
+        key_hash=key_hash,
+        reserved_msats=max_cost_for_model,
+        charge_msats=total_cost_msats,
     )
-    safe_reserved = case(
-        (
-            col(ApiKey.reserved_balance) >= max_cost_for_model,
-            col(ApiKey.reserved_balance) - max_cost_for_model,
-        ),
-        else_=0,
-    )
-
-    stmt = (
-        update(ApiKey)
-        .where(col(ApiKey.hashed_key) == billing_key.hashed_key)
-        .values(
-            reserved_balance=safe_reserved,
-            reserved_at=cleared_reserved_at,
-            balance=col(ApiKey.balance) - total_cost_msats,
-            total_spent=col(ApiKey.total_spent) + total_cost_msats,
-        )
-    )
-    result = await session.exec(stmt)  # type: ignore[call-overload]
-
-    if billing_key.hashed_key != key.hashed_key:
-        child_safe_reserved = case(
-            (
-                col(ApiKey.reserved_balance) >= max_cost_for_model,
-                col(ApiKey.reserved_balance) - max_cost_for_model,
-            ),
-            else_=0,
-        )
-        child_cleared_reserved_at = case(
-            (
-                col(ApiKey.reserved_balance) - max_cost_for_model > 0,
-                col(ApiKey.reserved_at),
-            ),
-            else_=None,
-        )
-        child_stmt = (
-            update(ApiKey)
-            .where(col(ApiKey.hashed_key) == key.hashed_key)
-            .values(
-                reserved_balance=child_safe_reserved,
-                reserved_at=child_cleared_reserved_at,
-                total_spent=col(ApiKey.total_spent) + total_cost_msats,
-            )
-        )
-        child_result = await session.exec(child_stmt)  # type: ignore[call-overload]
-    else:
-        child_result = None
-
-    if result.rowcount == 0 or (child_result is not None and child_result.rowcount == 0):
-        await session.rollback()
+    if not charged:
         logger.error(
             "Failed to finalize EHBP max-cost payment",
             extra={
@@ -699,14 +632,13 @@ async def finalize_ehbp_max_cost_payment(
                 "billing_key_hash": billing_key_hash[:8] + "...",
                 "model": model_id,
                 "max_cost_for_model": max_cost_for_model,
-                "parent_rowcount": result.rowcount,
-                "child_rowcount": getattr(child_result, "rowcount", None),
             },
         )
-        return
+        await _release_failed_ehbp_charge(reservation, session)
+        return 0
 
     await session.commit()
-
+    await _stop_reservation_heartbeat(reservation.release_id)
     await session.refresh(billing_key)
     if billing_key.hashed_key != key.hashed_key:
         await session.refresh(key)
@@ -739,6 +671,7 @@ async def finalize_ehbp_max_cost_payment(
             "finalized_at": now,
         },
     )
+    return total_cost_msats
 
 
 async def send_cashu_refund(
@@ -893,10 +826,9 @@ async def forward_ehbp_request(
             cost_info = await _compute_ehbp_actual_cost(
                 usage_header, model_obj, max_cost_for_model
             )
-            # Use the actual served model for billing when it differs from
-            # the requested model.
             billing_model = cost_info.pop("actual_model", None) or model_obj.id
-            await finalize_ehbp_actual_cost_payment(
+            computed_msats = int(cost_info["total_msats"])
+            charged_msats = await finalize_ehbp_actual_cost_payment(
                 key,
                 session,
                 max_cost_for_model,
@@ -904,7 +836,14 @@ async def forward_ehbp_request(
                 cost_info,
                 reservation_snapshot,
             )
-            cost_data = {**cost_info, "total_usd": 0.0}
+            cost_data = {
+                **cost_info,
+                "total_msats": charged_msats,
+                "charged_msats": charged_msats,
+                "total_usd": 0.0,
+            }
+            if computed_msats != charged_msats:
+                cost_data["computed_msats"] = computed_msats
         else:
             logger.warning(
                 "EHBP usage metrics not found in headers or trailers, "
@@ -915,7 +854,7 @@ async def forward_ehbp_request(
                     "key_hash": key.hashed_key[:8] + "...",
                 },
             )
-            await finalize_ehbp_max_cost_payment(
+            charged_msats = await finalize_ehbp_max_cost_payment(
                 key,
                 session,
                 max_cost_for_model,
@@ -923,11 +862,14 @@ async def forward_ehbp_request(
                 reservation_snapshot,
             )
             cost_data = {
-                "total_msats": max_cost_for_model,
+                "total_msats": charged_msats,
+                "charged_msats": charged_msats,
                 "total_usd": 0.0,
                 "input_tokens": 0,
                 "output_tokens": 0,
             }
+            if charged_msats != max_cost_for_model:
+                cost_data["computed_msats"] = max_cost_for_model
 
         # Build the cost_info dict from what adjust_payment_for_tokens returned
         # or from the max-cost fallback. Fields match CostData/MaxCostData.dict().
@@ -940,6 +882,8 @@ async def forward_ehbp_request(
             "input_msats": cost_data.get("input_msats", 0),
             "output_msats": cost_data.get("output_msats", 0),
         }
+        if "computed_msats" in cost_data:
+            cost_info["computed_msats"] = cost_data["computed_msats"]
         cost_usd = cost_data.get("total_usd", 0.0)
 
         # Build response headers, filtering out hop-by-hop headers
@@ -1028,7 +972,9 @@ async def forward_ehbp_x_cashu_request(
         target_url = _resolve_ehbp_target_url(
             target.url, path, headers, provider_type, profile
         )
-        upstream_headers = _prepare_ehbp_upstream_headers(headers, target.headers, profile)
+        upstream_headers = _prepare_ehbp_upstream_headers(
+            headers, target.headers, profile
+        )
         request_body = await request.body()
 
         # Merge query params into the target URL
@@ -1076,9 +1022,7 @@ async def forward_ehbp_x_cashu_request(
             usage_source = (
                 "header"
                 if usage_header_name
-                and any(
-                    k.lower() == usage_header_name.lower() for k, _ in resp.headers
-                )
+                and any(k.lower() == usage_header_name.lower() for k, _ in resp.headers)
                 else ("trailer" if usage_header else "none")
             )
 
diff --git a/tests/integration/test_free_response_stale_reservation.py b/tests/integration/test_free_response_stale_reservation.py
index dadb6a6a..80f0e294 100644
--- a/tests/integration/test_free_response_stale_reservation.py
+++ b/tests/integration/test_free_response_stale_reservation.py
@@ -7,7 +7,7 @@ from unittest.mock import patch
 import pytest
 from sqlmodel.ext.asyncio.session import AsyncSession
 
-from routstr.core.db import ApiKey
+from routstr.core.db import ApiKey, ReservationRelease
 from routstr.payment.cost_calculation import CostData
 
 
@@ -34,20 +34,30 @@ def _cost_data(total_msats: int) -> CostData:
 
 
 @pytest.mark.asyncio
-async def test_overrun_charges_after_reservation_swept(
+async def test_overrun_with_corrupted_aggregate_releases_without_charging(
     integration_session: AsyncSession,
 ) -> None:
-    """Overrun finalize must charge even when the reservation was already released."""
-    from routstr.auth import adjust_payment_for_tokens, pay_for_request
+    """An overrun whose aggregate reservation was externally zeroed must not
+    charge: subtracting the reservation would have to clamp, which can erase
+    sibling reservations. The reservation is released and the charge dropped.
+    """
+    from routstr import auth
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
 
     deducted_max_cost = 990  # discounted reservation
     actual_token_cost = 1000  # actual cost overruns the reservation
 
-    # Sweeper has zeroed reserved_balance but left balance untouched.
+    # Something zeroed reserved_balance under an active durable reservation.
     key = _make_key(balance=1000, reserved=0)
+    key_hash = key.hashed_key
     integration_session.add(key)
     await integration_session.commit()
     await pay_for_request(key, deducted_max_cost, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
     key.reserved_balance = 0
     integration_session.add(key)
     await integration_session.commit()
@@ -61,20 +71,24 @@ async def test_overrun_charges_after_reservation_swept(
         "routstr.auth.calculate_cost",
         return_value=_cost_data(actual_token_cost),
     ):
-        await adjust_payment_for_tokens(
+        result = await adjust_payment_for_tokens(
             key, response_data, integration_session, deducted_max_cost, None, None
         )
 
-    await integration_session.refresh(key)
+    assert result["charged_msats"] == 0
+    integration_session.expunge_all()
+    key_row = await integration_session.get(ApiKey, key_hash)
+    assert key_row is not None
 
-    assert key.total_spent == actual_token_cost, (
-        f"Request was not billed (total_spent={key.total_spent}) — free response bug"
-    )
-    assert key.balance == 1000 - actual_token_cost, (
-        f"Balance not charged: {key.balance}"
-    )
-    assert key.balance >= 0
-    assert key.reserved_balance == 0
+    assert key_row.total_spent == 0, "corrupted aggregate must not be charged into"
+    assert key_row.balance == 1000
+    assert key_row.reserved_balance == 0
+
+    # The corrupt reservation must reach a terminal state — an active leftover
+    # would be renewed by its heartbeat forever and poison stale cleanup.
+    record = await integration_session.get(ReservationRelease, reservation.release_id)
+    assert record is not None and record.status == "released"
+    assert reservation.release_id not in auth._reservation_heartbeats
 
 
 @pytest.mark.asyncio
diff --git a/tests/integration/test_negative_available_balance_repro.py b/tests/integration/test_negative_available_balance_repro.py
new file mode 100644
index 00000000..b31769f1
--- /dev/null
+++ b/tests/integration/test_negative_available_balance_repro.py
@@ -0,0 +1,747 @@
+"""Regression tests for the production "negative available balance" 402.
+
+Invariants protected:
+* billing and the admin API agree on what "available" means
+* an in-flight (heartbeaten) reservation is never swept; an abandoned one is
+  released and can never be charged afterwards
+* a cost overrun spends only its own reservation plus unreserved balance
+* corrupt reservations are repaired terminally instead of poisoning cleanup
+* under concurrency, balance / reserved / available never go negative
+"""
+
+import asyncio
+import random
+import time
+import uuid
+from typing import Awaitable, Callable
+from unittest.mock import patch
+
+import pytest
+from httpx import AsyncClient
+from sqlmodel import col, func, select, update
+from sqlmodel.ext.asyncio.session import AsyncSession
+
+from routstr.core.db import ApiKey, ReservationRelease
+from routstr.payment.cost_calculation import CostData
+
+pytestmark = pytest.mark.integration
+
+# Realistic sweeper timeout: a renewed (heartbeaten) reservation stays alive,
+# a reservation backdated past this is released.
+STALE_TIMEOUT_SECONDS = 300
+
+# created_at is whole seconds; -1 makes every reservation stale immediately.
+# Only used in the fuzz test to stress the terminal-release path.
+SWEEP_EVERYTHING = -1
+
+
+def _cost_data(total_msats: int) -> CostData:
+    return CostData(
+        base_msats=0,
+        input_msats=total_msats // 2,
+        output_msats=total_msats - total_msats // 2,
+        total_msats=total_msats,
+        total_usd=0.0,
+        input_tokens=100,
+        output_tokens=100,
+    )
+
+
+def _response(model: str = "test-model") -> dict:
+    return {
+        "model": model,
+        "usage": {"prompt_tokens": 100, "completion_tokens": 100},
+    }
+
+
+async def _new_key(session: AsyncSession, balance: int) -> str:
+    key_hash = f"test_neg_{uuid.uuid4().hex}"
+    session.add(
+        ApiKey(
+            hashed_key=key_hash,
+            balance=balance,
+            reserved_balance=0,
+            total_spent=0,
+            total_requests=0,
+        )
+    )
+    await session.commit()
+    return key_hash
+
+
+async def _backdate_reservation(
+    session: AsyncSession, release_id: str, seconds: int
+) -> None:
+    """Age a reservation's lease as if it had not been renewed for `seconds`."""
+    await session.exec(  # type: ignore[call-overload]
+        update(ReservationRelease)
+        .where(col(ReservationRelease.id) == release_id)
+        .values(created_at=col(ReservationRelease.created_at) - seconds)
+    )
+    await session.commit()
+
+
+async def _wait_for(
+    predicate: "Callable[[], Awaitable[bool]]",
+    timeout: float = 10.0,
+    interval: float = 0.1,
+) -> bool:
+    """Bounded polling instead of fixed sleeps for background-task effects."""
+    deadline = asyncio.get_event_loop().time() + timeout
+    while True:
+        if await predicate():
+            return True
+        if asyncio.get_event_loop().time() > deadline:
+            return False
+        await asyncio.sleep(interval)
+
+
+@pytest.mark.asyncio
+async def test_402_reports_negative_available_while_admin_shows_positive(
+    integration_session: AsyncSession,
+    integration_client: AsyncClient,
+) -> None:
+    """The production symptom: billing rejects on balance - reserved_balance,
+    so the admin endpoint must expose reserved/available, not just balance."""
+    from fastapi import HTTPException
+
+    from routstr.auth import _validate_bearer_key_locked
+    from routstr.core.db import set_admin_password
+
+    key_hash = await _new_key(integration_session, balance=263_000)
+    # Leaked reservations slightly exceeding the balance, as in production.
+    await integration_session.exec(  # type: ignore[call-overload]
+        update(ApiKey)
+        .where(col(ApiKey.hashed_key) == key_hash)
+        .values(reserved_balance=267_215)
+    )
+    await integration_session.commit()
+
+    with pytest.raises(HTTPException) as exc:
+        await _validate_bearer_key_locked(
+            "sk-" + key_hash, integration_session, min_cost=1
+        )
+
+    assert exc.value.status_code == 402
+    message = exc.value.detail["error"]["message"]  # type: ignore[index]
+    assert "-4.215 sats (-4215 msats) available" in message, message
+
+    await set_admin_password(integration_session, "test-admin-pw")
+    login = await integration_client.post(
+        "/admin/api/login", json={"password": "test-admin-pw"}
+    )
+    assert login.status_code == 200
+    token = login.json()["token"]
+    resp = await integration_client.get(
+        "/admin/api/temporary-balances",
+        params={"search": key_hash},
+        headers={"Authorization": f"Bearer {token}"},
+    )
+    assert resp.status_code == 200
+    rows = [row for row in resp.json()["balances"] if row["hashed_key"] == key_hash]
+    assert len(rows) == 1
+    row = rows[0]
+    assert row["balance"] == 263_000
+    assert row["reserved_balance"] == 267_215
+    assert row["available_balance"] == -4_215
+    assert resp.json()["totals"] == {
+        "total_balance": 263_000,
+        "total_reserved_balance": 267_215,
+        "total_available_balance": -4_215,
+        "total_spent": 0,
+        "total_requests": 0,
+    }
+
+
+@pytest.mark.asyncio
+async def test_abandoned_reservation_is_swept_and_cannot_finalize(
+    integration_session: AsyncSession,
+) -> None:
+    """Release is terminal: a swept reservation's late finalizer must not
+    charge, or it could spend funds since reserved by another request."""
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+    from routstr.core.db import release_stale_reservations
+
+    cost = 5_000
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, cost, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    # Client vanished: the lease is never renewed and ages past the timeout.
+    await _backdate_reservation(
+        integration_session, reservation.release_id, STALE_TIMEOUT_SECONDS + 1
+    )
+    released = await release_stale_reservations(
+        integration_session, STALE_TIMEOUT_SECONDS
+    )
+    assert released == 1
+
+    # A zombie finalizer shows up afterwards; it must not charge.
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(cost)):
+        await adjust_payment_for_tokens(
+            key,
+            _response(),
+            integration_session,
+            cost,
+            reservation_snapshot=reservation,
+        )
+
+    await integration_session.refresh(key)
+    record = await integration_session.get(ReservationRelease, reservation.release_id)
+    assert record is not None and record.status == "released"
+    assert key.total_spent == 0
+    assert key.balance == 10_000
+    assert key.reserved_balance == 0
+
+
+@pytest.mark.asyncio
+async def test_sweeper_cannot_release_a_reservation_renewed_after_selection(
+    integration_session: AsyncSession,
+) -> None:
+    """A heartbeat landing between the sweeper's select and its transition
+    must win — exercised through the public sweeper entry point."""
+    from routstr.auth import (
+        get_reservation_snapshot,
+        pay_for_request,
+        renew_reservation,
+    )
+    from routstr.core import db as core_db
+    from routstr.core.db import release_stale_reservations
+
+    key_hash = await _new_key(integration_session, balance=1_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+    await pay_for_request(key, 1_000, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    await _backdate_reservation(
+        integration_session, reservation.release_id, STALE_TIMEOUT_SECONDS + 100
+    )
+
+    real_transition = core_db._transition_stale_reservation
+
+    async def renew_then_transition(
+        session: AsyncSession, reservation_id: str, cutoff: int
+    ) -> bool:
+        # The sweeper selected this reservation as stale; the heartbeat
+        # renews exactly between that select and the transition.
+        assert await renew_reservation(reservation, session)
+        return await real_transition(session, reservation_id, cutoff)
+
+    with patch.object(core_db, "_transition_stale_reservation", renew_then_transition):
+        released = await release_stale_reservations(
+            integration_session, STALE_TIMEOUT_SECONDS
+        )
+
+    assert released == 0
+    record = await integration_session.get(ReservationRelease, reservation.release_id)
+    assert record is not None and record.status == "active"
+    await integration_session.refresh(key)
+    assert key.reserved_balance == 1_000
+
+
+@pytest.mark.asyncio
+async def test_legacy_cleanup_cannot_erase_a_reservation_committed_after_its_read(
+    integration_session: AsyncSession,
+) -> None:
+    """A reservation committing between the legacy sweep's read and its
+    zeroing must survive — exercised through the public sweeper entry point."""
+    from routstr.core import db as core_db
+    from routstr.core.db import release_stale_reservations
+
+    key_hash = await _new_key(integration_session, balance=10_000)
+    stale_reserved_at = int(time.time()) - (STALE_TIMEOUT_SECONDS + 100)
+    await integration_session.exec(  # type: ignore[call-overload]
+        update(ApiKey)
+        .where(col(ApiKey.hashed_key) == key_hash)
+        .values(reserved_balance=500, reserved_at=stale_reserved_at)
+    )
+    await integration_session.commit()
+
+    real_release = core_db._release_legacy_aggregate
+
+    async def commit_reservation_then_release(
+        session: AsyncSession,
+        target_key_hash: str,
+        observed_reserved: int,
+        observed_reserved_at: int | None,
+    ) -> bool:
+        # The sweeper read the legacy aggregate and found no active durable
+        # owner; a new reservation commits exactly before the zeroing lands.
+        session.add(
+            ReservationRelease(
+                id=uuid.uuid4().hex,
+                key_hash=target_key_hash,
+                billing_key_hash=target_key_hash,
+                reserved_msats=700,
+                status="active",
+            )
+        )
+        await session.exec(  # type: ignore[call-overload]
+            update(ApiKey)
+            .where(col(ApiKey.hashed_key) == target_key_hash)
+            .values(
+                reserved_balance=col(ApiKey.reserved_balance) + 700,
+                reserved_at=int(time.time()),
+            )
+        )
+        await session.commit()
+        return await real_release(
+            session, target_key_hash, observed_reserved, observed_reserved_at
+        )
+
+    with patch.object(
+        core_db, "_release_legacy_aggregate", commit_reservation_then_release
+    ):
+        released = await release_stale_reservations(
+            integration_session, STALE_TIMEOUT_SECONDS
+        )
+
+    assert released == 0
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+    assert key.reserved_balance == 1_200, "legacy cleanup erased a live reservation"
+
+
+@pytest.mark.asyncio
+async def test_sweeper_repairs_corrupt_reservation_and_continues_batch(
+    integration_session: AsyncSession,
+) -> None:
+    """One corrupt durable reservation (aggregate no longer holds its msats)
+    must be terminalized without aggregate subtraction, and must not stop the
+    rest of the batch from being released normally."""
+    from routstr.auth import get_reservation_snapshot, pay_for_request
+    from routstr.core.db import release_stale_reservations
+
+    cost = 1_000
+    corrupt_hash = await _new_key(integration_session, balance=cost)
+    healthy_hash = await _new_key(integration_session, balance=cost)
+
+    corrupt_key = await integration_session.get(ApiKey, corrupt_hash)
+    assert corrupt_key is not None
+    await pay_for_request(corrupt_key, cost, integration_session)
+    corrupt_reservation = await get_reservation_snapshot(
+        corrupt_key, integration_session
+    )
+
+    healthy_key = await integration_session.get(ApiKey, healthy_hash)
+    assert healthy_key is not None
+    await pay_for_request(healthy_key, cost, integration_session)
+    healthy_reservation = await get_reservation_snapshot(
+        healthy_key, integration_session
+    )
+
+    # Corrupt the first key: its aggregate no longer holds the reservation.
+    await integration_session.exec(  # type: ignore[call-overload]
+        update(ApiKey)
+        .where(col(ApiKey.hashed_key) == corrupt_hash)
+        .values(reserved_balance=0)
+    )
+    await integration_session.commit()
+
+    for reservation in (corrupt_reservation, healthy_reservation):
+        await _backdate_reservation(
+            integration_session, reservation.release_id, STALE_TIMEOUT_SECONDS + 100
+        )
+
+    released = await release_stale_reservations(
+        integration_session, STALE_TIMEOUT_SECONDS
+    )
+    assert released == 2, "a corrupt record must not abort the sweep batch"
+
+    for reservation in (corrupt_reservation, healthy_reservation):
+        record = await integration_session.get(
+            ReservationRelease, reservation.release_id
+        )
+        assert record is not None and record.status == "released"
+    healthy_key = await integration_session.get(ApiKey, healthy_hash)
+    corrupt_key = await integration_session.get(ApiKey, corrupt_hash)
+    assert healthy_key is not None and corrupt_key is not None
+    assert healthy_key.reserved_balance == 0
+    assert corrupt_key.reserved_balance == 0
+    assert corrupt_key.balance == cost, "repair must not touch balances"
+
+
+@pytest.mark.asyncio
+async def test_heartbeat_survives_a_rolled_back_charge_attempt(
+    integration_session: AsyncSession,
+    patched_db_engine: None,
+) -> None:
+    """Claiming a reservation must not stop its heartbeat: a rollback restores
+    the active reservation, which then still needs lease renewal."""
+    from routstr import auth
+    from routstr.auth import (
+        _claim_reservation_for_charge,
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+    from routstr.core.db import create_session
+
+    cost = 1_000
+    timeout = 3  # heartbeat interval = 1s
+    with patch.object(auth.settings, "stale_reservation_timeout_seconds", timeout):
+        async with create_session() as session:
+            key_hash = await _new_key(session, balance=2_000)
+            key = await session.get(ApiKey, key_hash)
+            assert key is not None
+            await pay_for_request(key, cost, session)
+            reservation = await get_reservation_snapshot(key, session)
+
+        try:
+            # A charge attempt claims the reservation, then its transaction
+            # fails and rolls back.
+            async with create_session() as session:
+                assert await _claim_reservation_for_charge(reservation, session)
+                await session.rollback()
+
+            async with create_session() as session:
+                record = await session.get(ReservationRelease, reservation.release_id)
+                assert record is not None and record.status == "active"
+                await _backdate_reservation(
+                    session, reservation.release_id, timeout * 10
+                )
+                record = await session.get(ReservationRelease, reservation.release_id)
+                assert record is not None
+                backdated_lease = record.created_at
+
+            async def lease_renewed() -> bool:
+                async with create_session() as session:
+                    record = await session.get(
+                        ReservationRelease, reservation.release_id
+                    )
+                    return record is not None and record.created_at > backdated_lease
+
+            assert await _wait_for(lease_renewed), (
+                "heartbeat did not survive the rolled-back charge attempt"
+            )
+
+            # The restored reservation still finalizes normally.
+            with patch("routstr.auth.calculate_cost", return_value=_cost_data(cost)):
+                async with create_session() as session:
+                    key = await session.get(ApiKey, key_hash)
+                    assert key is not None
+                    result = await adjust_payment_for_tokens(
+                        key,
+                        _response(),
+                        session,
+                        cost,
+                        reservation_snapshot=reservation,
+                    )
+        finally:
+            await auth._stop_reservation_heartbeat(reservation.release_id)
+
+    assert result["charged_msats"] == cost
+    async with create_session() as session:
+        record = await session.get(ReservationRelease, reservation.release_id)
+        assert record is not None and record.status == "charged"
+        key = await session.get(ApiKey, key_hash)
+        assert key is not None
+        assert key.total_spent == cost
+
+
+@pytest.mark.asyncio
+async def test_heartbeat_dies_with_its_request_so_sweeper_can_recover(
+    integration_session: AsyncSession,
+    patched_db_engine: None,
+) -> None:
+    """A request that vanishes without finalizing must not renew forever —
+    its heartbeat stops with the owning task and the sweeper reclaims the
+    funds."""
+    from routstr import auth
+    from routstr.auth import get_reservation_snapshot, pay_for_request
+    from routstr.core.db import create_session, release_stale_reservations
+
+    cost = 1_000
+    timeout = 3  # heartbeat interval = 1s
+    async with create_session() as session:
+        key_hash = await _new_key(session, balance=cost)
+
+    holder: dict = {}
+    with patch.object(auth.settings, "stale_reservation_timeout_seconds", timeout):
+
+        async def doomed_request() -> None:
+            async with create_session() as session:
+                key = await session.get(ApiKey, key_hash)
+                assert key is not None
+                await pay_for_request(key, cost, session)
+                holder["reservation"] = await get_reservation_snapshot(key, session)
+            # ...request control dies here, no finalize and no release.
+
+        await asyncio.create_task(doomed_request())
+        release_id = holder["reservation"].release_id
+
+        try:
+            # While the heartbeat is still winding down it may renew once
+            # more; keep backdating until the sweeper wins, which it must as
+            # soon as the dead owner is noticed.
+            async def sweeper_recovered() -> bool:
+                async with create_session() as session:
+                    await _backdate_reservation(session, release_id, timeout * 10)
+                    return await release_stale_reservations(session, timeout) == 1
+
+            assert await _wait_for(sweeper_recovered), (
+                "sweeper never recovered the abandoned reservation"
+            )
+        finally:
+            await auth._stop_reservation_heartbeat(release_id)
+
+        async with create_session() as session:
+            record = await session.get(ReservationRelease, release_id)
+            assert record is not None and record.status == "released"
+            key = await session.get(ApiKey, key_hash)
+            assert key is not None
+            assert key.reserved_balance == 0
+            assert key.total_spent == 0
+
+
+@pytest.mark.asyncio
+async def test_reservation_heartbeat_covers_the_whole_request_lifecycle(
+    integration_session: AsyncSession,
+    patched_db_engine: None,
+) -> None:
+    """pay_for_request starts the heartbeat, finalization stops it, and a
+    backdated lease is renewed in the background without any manual call."""
+    from routstr import auth
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+    from routstr.core.db import create_session, release_stale_reservations
+
+    cost = 1_000
+    timeout = 3  # heartbeat interval = 1s
+    async with create_session() as session:
+        key_hash = await _new_key(session, balance=2 * cost)
+
+    with patch.object(auth.settings, "stale_reservation_timeout_seconds", timeout):
+        async with create_session() as session:
+            key = await session.get(ApiKey, key_hash)
+            assert key is not None
+            await pay_for_request(key, cost, session)
+            reservation = await get_reservation_snapshot(key, session)
+
+        try:
+            # Only a background renewal can keep this alive now.
+            async with create_session() as session:
+                await _backdate_reservation(
+                    session, reservation.release_id, timeout * 10
+                )
+                record = await session.get(ReservationRelease, reservation.release_id)
+                assert record is not None
+                backdated_lease = record.created_at
+
+            async def lease_renewed() -> bool:
+                async with create_session() as session:
+                    record = await session.get(
+                        ReservationRelease, reservation.release_id
+                    )
+                    return record is not None and record.created_at > backdated_lease
+
+            assert await _wait_for(lease_renewed), "heartbeat never renewed the lease"
+            async with create_session() as session:
+                assert await release_stale_reservations(session, timeout) == 0
+
+            with patch("routstr.auth.calculate_cost", return_value=_cost_data(cost)):
+                async with create_session() as session:
+                    key = await session.get(ApiKey, key_hash)
+                    assert key is not None
+                    result = await adjust_payment_for_tokens(
+                        key,
+                        _response(),
+                        session,
+                        cost,
+                        reservation_snapshot=reservation,
+                    )
+        finally:
+            await auth._stop_reservation_heartbeat(reservation.release_id)
+
+    assert result["charged_msats"] == cost
+    async with create_session() as session:
+        record = await session.get(ReservationRelease, reservation.release_id)
+        assert record is not None and record.status == "charged"
+        key = await session.get(ApiKey, key_hash)
+        assert key is not None
+        assert key.total_spent == cost
+        assert key.reserved_balance == 0
+
+
+@pytest.mark.asyncio
+async def test_overrun_cannot_spend_a_concurrent_reservation(
+    integration_session: AsyncSession,
+) -> None:
+    """An overrun is capped to its own reservation plus unreserved balance;
+    the sibling's reserved funds stay untouched and available stays >= 0."""
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    reserved_each = 100
+    overrun_cost = 150  # A's real token cost exceeds its reservation
+
+    # Balance covers exactly two reservations; nothing free on top.
+    key_hash = await _new_key(integration_session, balance=2 * reserved_each)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, reserved_each, integration_session)
+    reservation_a = await get_reservation_snapshot(key, integration_session)
+    await pay_for_request(key, reserved_each, integration_session)
+    await get_reservation_snapshot(key, integration_session)  # B stays in flight
+
+    await integration_session.refresh(key)
+    assert key.reserved_balance == 2 * reserved_each
+
+    # Only A finalizes; B is still streaming and its funds must stay reserved.
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(overrun_cost)):
+        result = await adjust_payment_for_tokens(
+            key,
+            _response(),
+            integration_session,
+            reserved_each,
+            reservation_snapshot=reservation_a,
+        )
+
+    assert result["charged_msats"] == reserved_each
+    assert result["total_msats"] == overrun_cost
+    await integration_session.refresh(key)
+    assert key.total_spent == reserved_each
+    assert key.reserved_balance == reserved_each
+    assert key.balance == reserved_each
+    assert key.total_balance >= 0, (
+        f"available balance went negative: balance={key.balance} "
+        f"reserved={key.reserved_balance} -> {key.total_balance} msats; "
+        "the overrun charge consumed the still-reserved funds of request B"
+    )
+
+
+@pytest.mark.asyncio
+async def test_concurrent_requests_with_sweeper_keep_balance_invariants(
+    integration_session: AsyncSession,
+    patched_db_engine: None,
+) -> None:
+    """Fuzz: concurrent requests against an everything-is-stale sweeper.
+    Some requests legitimately finish uncharged (release is terminal), but
+    balances must never go negative and no reservation may stay active."""
+    from fastapi import HTTPException
+
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+    from routstr.core.db import create_session, release_stale_reservations
+
+    rng = random.Random(1337)
+    starting_balance = 200_000
+    n_requests = 24
+
+    async with create_session() as session:
+        key_hash = await _new_key(session, balance=starting_balance)
+
+    completed_costs: list[int] = []
+    rejected_requests = 0
+
+    async def one_request(index: int) -> None:
+        nonlocal rejected_requests
+        reserved = rng.randrange(1_000, 4_000)
+        actual = max(1, int(reserved * rng.uniform(0.5, 1.1)))
+        try:
+            async with create_session() as session:
+                key = await session.get(ApiKey, key_hash)
+                assert key is not None
+                await pay_for_request(key, reserved, session)
+        except HTTPException as exc:
+            # A depleted balance is the only legitimate rejection.
+            assert exc.status_code == 402, exc.detail
+            rejected_requests += 1
+            return
+
+        try:
+            async with create_session() as session:
+                key = await session.get(ApiKey, key_hash)
+                assert key is not None
+                reservation = await get_reservation_snapshot(key, session)
+        except RuntimeError:
+            # The everything-is-stale sweeper can release the reservation
+            # before the stream even starts; the request aborts uncharged.
+            return
+
+        await asyncio.sleep(rng.uniform(0, 0.02))  # the "stream"
+
+        async with create_session() as session:
+            key = await session.get(ApiKey, key_hash)
+            assert key is not None
+            await adjust_payment_for_tokens(
+                key,
+                _response(str(actual)),
+                session,
+                reserved,
+                reservation_snapshot=reservation,
+            )
+        completed_costs.append(actual)
+
+    sweeping = True
+
+    async def sweeper() -> None:
+        while sweeping:
+            async with create_session() as session:
+                await release_stale_reservations(session, SWEEP_EVERYTHING)
+            await asyncio.sleep(0.002)
+
+    sweep_task = asyncio.create_task(sweeper())
+    try:
+        with patch(
+            "routstr.auth.calculate_cost",
+            side_effect=lambda response_data, *a, **k: _cost_data(
+                int(response_data["model"])
+            ),
+        ):
+            await asyncio.gather(*(one_request(i) for i in range(n_requests)))
+    finally:
+        sweeping = False
+        await sweep_task
+
+    async with create_session() as session:
+        key = await session.get(ApiKey, key_hash)
+        assert key is not None
+        leftover_active = (
+            await session.exec(  # type: ignore[call-overload]
+                select(func.count())
+                .select_from(ReservationRelease)
+                .where(col(ReservationRelease.status) == "active")
+            )
+        ).one()
+
+    assert completed_costs or rejected_requests, "no request made any progress"
+    assert key.balance >= 0, f"balance went negative: {key.balance}"
+    assert key.reserved_balance >= 0, (
+        f"reserved_balance went negative: {key.reserved_balance}"
+    )
+    assert key.total_balance >= 0, (
+        f"available balance negative: balance={key.balance} "
+        f"reserved={key.reserved_balance} (this is the production symptom)"
+    )
+    assert key.total_spent <= starting_balance, (
+        f"spent {key.total_spent} of a {starting_balance} balance"
+    )
+    # Requests whose reservation was swept mid-flight finish uncharged, so the
+    # charged total can only be at most the sum of completed request costs.
+    max_expected_spend = sum(completed_costs)
+    assert key.total_spent <= max_expected_spend, (
+        f"charged {key.total_spent} msats but completed requests only cost "
+        f"{max_expected_spend}"
+    )
+    assert leftover_active == 0, (
+        f"{leftover_active} reservations still active after all requests finished"
+    )
diff --git a/tests/integration/test_payment_invariants.py b/tests/integration/test_payment_invariants.py
new file mode 100644
index 00000000..ca7bf892
--- /dev/null
+++ b/tests/integration/test_payment_invariants.py
@@ -0,0 +1,549 @@
+"""Invariant coverage for the reserve → charge → release money path.
+
+Every finalization branch of ``adjust_payment_for_tokens`` must respect the
+same accounting rules: a completed request is charged exactly once, its
+reported ``charged_msats`` matches the actual debit, it never spends more than
+its own reservation leaves available, and child keys spend their parent's
+balance without raiding sibling reservations.
+"""
+
+import asyncio
+import uuid
+from unittest.mock import patch
+
+import pytest
+from fastapi import HTTPException
+from sqlmodel import col, select, update
+from sqlmodel.ext.asyncio.session import AsyncSession
+
+from routstr.core.db import ApiKey, ReservationRelease
+from routstr.payment.cost_calculation import (
+    CostData,
+    CostDataError,
+    MaxCostData,
+)
+
+pytestmark = pytest.mark.integration
+
+
+def _cost_data(total_msats: int, cls: type[CostData] = CostData) -> CostData:
+    return cls(
+        base_msats=0,
+        input_msats=total_msats // 2,
+        output_msats=total_msats - total_msats // 2,
+        total_msats=total_msats,
+        total_usd=0.0,
+        input_tokens=100,
+        output_tokens=100,
+    )
+
+
+def _response() -> dict:
+    return {
+        "model": "test-model",
+        "usage": {"prompt_tokens": 100, "completion_tokens": 100},
+    }
+
+
+async def _new_key(
+    session: AsyncSession,
+    balance: int,
+    *,
+    parent_key_hash: str | None = None,
+    balance_limit: int | None = None,
+) -> str:
+    key_hash = f"test_inv_{uuid.uuid4().hex}"
+    session.add(
+        ApiKey(
+            hashed_key=key_hash,
+            balance=balance,
+            reserved_balance=0,
+            total_spent=0,
+            total_requests=0,
+            parent_key_hash=parent_key_hash,
+            balance_limit=balance_limit,
+        )
+    )
+    await session.commit()
+    return key_hash
+
+
+async def _active_reservations(session: AsyncSession) -> int:
+    rows = await session.exec(
+        select(ReservationRelease).where(col(ReservationRelease.status) == "active")
+    )
+    return len(rows.all())
+
+
+@pytest.mark.asyncio
+async def test_corrupt_revert_still_decrements_request_count(
+    integration_session: AsyncSession,
+) -> None:
+    from routstr.auth import (
+        get_reservation_snapshot,
+        pay_for_request,
+        revert_pay_for_request,
+    )
+
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+    await pay_for_request(key, 3_000, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    await integration_session.exec(  # type: ignore[call-overload]
+        update(ApiKey)
+        .where(col(ApiKey.hashed_key) == key_hash)
+        .values(reserved_balance=0)
+    )
+    await integration_session.commit()
+
+    assert await revert_pay_for_request(
+        key,
+        integration_session,
+        3_000,
+        reservation_snapshot=reservation,
+    )
+    updated = await integration_session.get(ApiKey, key_hash)
+    record = await integration_session.get(ReservationRelease, reservation.release_id)
+    assert updated is not None
+    assert updated.total_requests == 0
+    assert updated.reserved_balance == 0
+    assert record is not None and record.status == "released"
+
+
+@pytest.mark.asyncio
+async def test_exact_cost_branch_charges_the_reservation_once(
+    integration_session: AsyncSession,
+) -> None:
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    cost = 3_000
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, cost, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(cost)):
+        result = await adjust_payment_for_tokens(
+            key,
+            _response(),
+            integration_session,
+            cost,
+            reservation_snapshot=reservation,
+        )
+
+    assert result["charged_msats"] == cost
+    await integration_session.refresh(key)
+    assert key.balance == 10_000 - cost
+    assert key.total_spent == cost
+    assert key.reserved_balance == 0
+    assert key.total_requests == 1
+    assert await _active_reservations(integration_session) == 0
+
+
+@pytest.mark.asyncio
+async def test_max_cost_branch_charges_the_reservation_once(
+    integration_session: AsyncSession,
+) -> None:
+    """No token pricing configured -> flat MaxCostData charge of the reservation."""
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    cost = 2_500
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, cost, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    with patch(
+        "routstr.auth.calculate_cost",
+        return_value=_cost_data(cost, cls=MaxCostData),
+    ):
+        result = await adjust_payment_for_tokens(
+            key,
+            _response(),
+            integration_session,
+            cost,
+            reservation_snapshot=reservation,
+        )
+
+    assert result["charged_msats"] == cost
+    await integration_session.refresh(key)
+    assert key.balance == 10_000 - cost
+    assert key.total_spent == cost
+    assert key.reserved_balance == 0
+
+
+@pytest.mark.asyncio
+async def test_underrun_branch_refunds_the_unused_reservation(
+    integration_session: AsyncSession,
+) -> None:
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    reserved = 5_000
+    actual = 1_200
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, reserved, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(actual)):
+        result = await adjust_payment_for_tokens(
+            key,
+            _response(),
+            integration_session,
+            reserved,
+            reservation_snapshot=reservation,
+        )
+
+    assert result["charged_msats"] == actual
+    await integration_session.refresh(key)
+    assert key.total_spent == actual, "user must pay the real cost, not the reservation"
+    assert key.balance == 10_000 - actual
+    assert key.reserved_balance == 0
+
+
+@pytest.mark.asyncio
+async def test_overrun_branch_charges_full_cost_when_balance_is_free(
+    integration_session: AsyncSession,
+) -> None:
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    reserved = 1_000
+    actual = 1_400
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, reserved, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(actual)):
+        result = await adjust_payment_for_tokens(
+            key,
+            _response(),
+            integration_session,
+            reserved,
+            reservation_snapshot=reservation,
+        )
+
+    assert result["charged_msats"] == actual
+    await integration_session.refresh(key)
+    assert key.total_spent == actual
+    assert key.balance == 10_000 - actual
+    assert key.reserved_balance == 0
+
+
+@pytest.mark.asyncio
+async def test_zero_cost_response_is_free_and_releases_the_reservation(
+    integration_session: AsyncSession,
+) -> None:
+    """An empty/unusable upstream response must cost the user nothing."""
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    reserved = 4_000
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, reserved, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(0)):
+        await adjust_payment_for_tokens(
+            key,
+            {"model": "test-model"},
+            integration_session,
+            reserved,
+            reservation_snapshot=reservation,
+        )
+
+    await integration_session.refresh(key)
+    assert key.balance == 10_000
+    assert key.total_spent == 0
+    assert key.reserved_balance == 0
+    assert await _active_reservations(integration_session) == 0
+
+
+@pytest.mark.asyncio
+async def test_cost_error_releases_the_reservation_without_charging(
+    integration_session: AsyncSession,
+) -> None:
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    reserved = 4_000
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, reserved, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    with patch(
+        "routstr.auth.calculate_cost",
+        return_value=CostDataError(message="no pricing", code="pricing_error"),
+    ):
+        with pytest.raises(HTTPException) as exc:
+            await adjust_payment_for_tokens(
+                key,
+                _response(),
+                integration_session,
+                reserved,
+                reservation_snapshot=reservation,
+            )
+    assert exc.value.status_code == 400
+
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+    assert key.balance == 10_000, "a pricing failure must not charge the user"
+    assert key.total_spent == 0
+    assert key.reserved_balance == 0, "funds must not stay locked after a 400"
+    assert await _active_reservations(integration_session) == 0
+
+
+@pytest.mark.asyncio
+async def test_repeated_finalization_charges_only_once(
+    integration_session: AsyncSession,
+) -> None:
+    """A retried finalizer (proxy retry, duplicate stream end) must not double-bill."""
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    cost = 3_000
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, cost, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    results = []
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(cost)):
+        for _ in range(3):
+            # A declined re-charge rolls its session back, so re-load the key
+            # the way a fresh request would instead of reusing a stale instance.
+            integration_session.expunge_all()
+            key = await integration_session.get(ApiKey, key_hash)
+            assert key is not None
+            results.append(
+                await adjust_payment_for_tokens(
+                    key,
+                    _response(),
+                    integration_session,
+                    cost,
+                    reservation_snapshot=reservation,
+                )
+            )
+
+    # Only the first finalization debits; duplicates report a zero charge.
+    assert [r["charged_msats"] for r in results] == [cost, 0, 0]
+
+    integration_session.expunge_all()
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+    assert key.total_spent == cost, f"charged {key.total_spent} for one request"
+    assert key.balance == 10_000 - cost
+
+
+@pytest.mark.asyncio
+async def test_concurrent_duplicate_finalization_charges_only_once(
+    integration_session: AsyncSession,
+    patched_db_engine: None,
+) -> None:
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+    from routstr.core.db import create_session
+
+    cost = 3_000
+    async with create_session() as session:
+        key_hash = await _new_key(session, balance=10_000)
+        key = await session.get(ApiKey, key_hash)
+        assert key is not None
+        await pay_for_request(key, cost, session)
+        reservation = await get_reservation_snapshot(key, session)
+
+    async def finalize() -> None:
+        async with create_session() as session:
+            fresh = await session.get(ApiKey, key_hash)
+            assert fresh is not None
+            await adjust_payment_for_tokens(
+                fresh,
+                _response(),
+                session,
+                cost,
+                reservation_snapshot=reservation,
+            )
+
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(cost)):
+        await asyncio.gather(finalize(), finalize(), finalize())
+
+    async with create_session() as session:
+        key = await session.get(ApiKey, key_hash)
+    assert key is not None
+    assert key.total_spent == cost
+    assert key.balance == 10_000 - cost
+    assert key.reserved_balance == 0
+
+
+@pytest.mark.asyncio
+async def test_release_after_charge_does_not_credit_the_user_back(
+    integration_session: AsyncSession,
+) -> None:
+    """A late cleanup path must not turn a charged request into a free one."""
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+        release_reservation,
+    )
+
+    cost = 3_000
+    key_hash = await _new_key(integration_session, balance=10_000)
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+
+    await pay_for_request(key, cost, integration_session)
+    reservation = await get_reservation_snapshot(key, integration_session)
+
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(cost)):
+        await adjust_payment_for_tokens(
+            key,
+            _response(),
+            integration_session,
+            cost,
+            reservation_snapshot=reservation,
+        )
+
+    released = await release_reservation(reservation, integration_session, cost)
+    assert released is False, "a charged reservation must not be releasable"
+
+    key = await integration_session.get(ApiKey, key_hash)
+    assert key is not None
+    assert key.balance == 10_000 - cost
+    assert key.total_spent == cost
+    assert key.reserved_balance == 0
+
+
+@pytest.mark.asyncio
+async def test_child_request_spends_parent_balance_and_records_child_ledger(
+    integration_session: AsyncSession,
+) -> None:
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    cost = 3_000
+    parent_hash = await _new_key(integration_session, balance=10_000)
+    child_hash = await _new_key(
+        integration_session, balance=0, parent_key_hash=parent_hash
+    )
+    child = await integration_session.get(ApiKey, child_hash)
+    assert child is not None
+
+    await pay_for_request(child, cost, integration_session)
+    reservation = await get_reservation_snapshot(child, integration_session)
+
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(cost)):
+        await adjust_payment_for_tokens(
+            child,
+            _response(),
+            integration_session,
+            cost,
+            reservation_snapshot=reservation,
+        )
+
+    parent = await integration_session.get(ApiKey, parent_hash)
+    child = await integration_session.get(ApiKey, child_hash)
+    assert parent is not None and child is not None
+    assert parent.balance == 10_000 - cost
+    assert parent.reserved_balance == 0
+    assert parent.total_balance >= 0
+    assert child.reserved_balance == 0, "child reservation must be released too"
+    assert child.total_balance >= 0
+    assert child.total_spent == cost, "child ledger must record the spend"
+    assert parent.total_spent == cost
+
+
+@pytest.mark.asyncio
+async def test_child_overrun_does_not_raid_a_sibling_reservation(
+    integration_session: AsyncSession,
+) -> None:
+    """Same overrun defect as the parent case, reached through a child key."""
+    from routstr.auth import (
+        adjust_payment_for_tokens,
+        get_reservation_snapshot,
+        pay_for_request,
+    )
+
+    reserved_each = 100
+    overrun = 150
+    parent_hash = await _new_key(integration_session, balance=2 * reserved_each)
+    child_a = await _new_key(
+        integration_session, balance=0, parent_key_hash=parent_hash
+    )
+    child_b = await _new_key(
+        integration_session, balance=0, parent_key_hash=parent_hash
+    )
+
+    key_a = await integration_session.get(ApiKey, child_a)
+    key_b = await integration_session.get(ApiKey, child_b)
+    assert key_a is not None and key_b is not None
+
+    await pay_for_request(key_a, reserved_each, integration_session)
+    reservation_a = await get_reservation_snapshot(key_a, integration_session)
+    await pay_for_request(key_b, reserved_each, integration_session)
+    await get_reservation_snapshot(key_b, integration_session)
+
+    with patch("routstr.auth.calculate_cost", return_value=_cost_data(overrun)):
+        await adjust_payment_for_tokens(
+            key_a,
+            _response(),
+            integration_session,
+            reserved_each,
+            reservation_snapshot=reservation_a,
+        )
+
+    parent = await integration_session.get(ApiKey, parent_hash)
+    assert parent is not None
+    assert parent.total_balance >= 0, (
+        f"child A's overrun ate child B's reservation: balance={parent.balance} "
+        f"reserved={parent.reserved_balance}"
+    )
diff --git a/tests/integration/test_reserved_balance_negative.py b/tests/integration/test_reserved_balance_negative.py
index 8ffebc86..d8e2846e 100644
--- a/tests/integration/test_reserved_balance_negative.py
+++ b/tests/integration/test_reserved_balance_negative.py
@@ -133,14 +133,11 @@ async def test_reserved_balance_with_successful_requests(
 
 
 @pytest.mark.asyncio
-async def test_revert_with_zero_reserved_balance_is_noop(
+async def test_revert_with_zero_reserved_balance_repairs_terminally(
     integration_session: AsyncSession,
 ) -> None:
-    """Test that revert_pay_for_request is a no-op when reserved_balance is 0.
-
-    Previously this would drive reserved_balance negative. With the floor guard,
-    it should return False and leave reserved_balance at 0.
-    """
+    """Reverting after the aggregate was already zeroed must not drive it
+    negative: the corrupt durable reservation is released without subtraction."""
     from routstr.auth import pay_for_request, revert_pay_for_request
 
     unique_key = f"test_revert_key_{uuid.uuid4().hex[:8]}"
@@ -153,21 +150,66 @@ async def test_revert_with_zero_reserved_balance_is_noop(
     await integration_session.commit()
     await pay_for_request(test_key, 100, integration_session)
     test_key.reserved_balance = 0
+    test_key.total_requests = 0
     integration_session.add(test_key)
     await integration_session.commit()
 
-    # A stale cleanup already released the aggregate reservation.
+    # A stale cleanup already released the aggregate reservation. The revert
+    # terminalizes the durable row (repair) without driving the aggregate
+    # negative.
     result = await revert_pay_for_request(test_key, integration_session, 100)
 
-    await integration_session.refresh(test_key)
+    integration_session.expunge_all()
+    test_key = await integration_session.get(ApiKey, unique_key)
+    assert test_key is not None
 
-    assert result is False, "Revert should return False when reservation already released"
+    assert result is True, "Revert must terminalize the corrupt reservation"
     assert test_key.reserved_balance == 0, (
         f"Reserved balance should remain 0, got: {test_key.reserved_balance}"
     )
-    assert test_key.total_requests == 1, (
-        f"Total requests should remain 1, got: {test_key.total_requests}"
+    assert test_key.total_requests == 0
+
+
+@pytest.mark.asyncio
+async def test_child_corrupt_revert_clamps_zero_request_counts(
+    integration_session: AsyncSession,
+) -> None:
+    from routstr.auth import (
+        get_reservation_snapshot,
+        pay_for_request,
+        revert_pay_for_request,
     )
+    from routstr.core.db import ReservationRelease
+
+    suffix = uuid.uuid4().hex[:8]
+    parent = ApiKey(hashed_key=f"repair-parent-{suffix}", balance=5_000)
+    child = ApiKey(
+        hashed_key=f"repair-child-{suffix}",
+        parent_key_hash=parent.hashed_key,
+    )
+    integration_session.add(parent)
+    integration_session.add(child)
+    await integration_session.commit()
+    await pay_for_request(child, 500, integration_session)
+    snapshot = await get_reservation_snapshot(child, integration_session)
+
+    parent.total_requests = 0
+    child.total_requests = 0
+    child.reserved_balance = 0
+    integration_session.add(parent)
+    integration_session.add(child)
+    await integration_session.commit()
+
+    assert await revert_pay_for_request(child, integration_session, 500, snapshot)
+
+    integration_session.expunge_all()
+    parent = await integration_session.get(ApiKey, snapshot.billing_key_hash)
+    child = await integration_session.get(ApiKey, snapshot.key_hash)
+    release = await integration_session.get(ReservationRelease, snapshot.release_id)
+    assert parent is not None and child is not None
+    assert (parent.total_requests, child.total_requests) == (0, 0)
+    assert (parent.reserved_balance, child.reserved_balance) == (500, 0)
+    assert release is not None and release.status == "released"
 
 
 @pytest.mark.asyncio
@@ -203,10 +245,11 @@ async def test_revert_with_sufficient_reserved_balance_succeeds(
 
 
 @pytest.mark.asyncio
-async def test_revert_partial_reserved_balance_is_noop(
+async def test_revert_partial_reserved_balance_repairs_terminally(
     integration_session: AsyncSession,
 ) -> None:
-    """Test that reverting more than the current reserved_balance is a no-op."""
+    """Reverting more than the aggregate holds must not clamp or go negative:
+    the corrupt durable reservation is released without subtraction."""
     from routstr.auth import pay_for_request, revert_pay_for_request
 
     unique_key = f"test_revert_partial_{uuid.uuid4().hex[:8]}"
@@ -223,18 +266,19 @@ async def test_revert_partial_reserved_balance_is_noop(
     integration_session.add(test_key)
     await integration_session.commit()
 
-    # Try to revert 500 when only 50 is reserved — should be no-op
+    # Reverting 500 when only 50 is reserved cannot subtract; the corrupt
+    # reservation is terminalized and the aggregate left untouched.
     result = await revert_pay_for_request(test_key, integration_session, 500)
 
-    await integration_session.refresh(test_key)
+    integration_session.expunge_all()
+    test_key = await integration_session.get(ApiKey, unique_key)
+    assert test_key is not None
 
-    assert result is False, "Revert should fail when cost > reserved_balance"
+    assert result is True, "Revert must terminalize the corrupt reservation"
     assert test_key.reserved_balance == 50, (
         f"Reserved balance should stay at 50, got: {test_key.reserved_balance}"
     )
-    assert test_key.total_requests == 1, (
-        f"Total requests should stay at 1, got: {test_key.total_requests}"
-    )
+    assert test_key.total_requests == 0
 
 
 @pytest.mark.asyncio
@@ -265,9 +309,7 @@ async def test_double_revert_prevented(
     snapshot = await get_reservation_snapshot(test_key, integration_session)
 
     # First revert — should succeed
-    result1 = await revert_pay_for_request(
-        test_key, integration_session, 500, snapshot
-    )
+    result1 = await revert_pay_for_request(test_key, integration_session, 500, snapshot)
     await integration_session.refresh(test_key)
 
     assert result1 is True
@@ -275,9 +317,7 @@ async def test_double_revert_prevented(
     assert test_key.total_requests == 4
 
     # Second revert of the same amount — should be no-op
-    result2 = await revert_pay_for_request(
-        test_key, integration_session, 500, snapshot
-    )
+    result2 = await revert_pay_for_request(test_key, integration_session, 500, snapshot)
     await integration_session.refresh(test_key)
 
     assert result2 is False, "Second revert should be a no-op"
@@ -319,9 +359,7 @@ async def test_sequential_reverts_never_go_negative(
     # Run 5 sequential reverts for the same 500 reservation
     results = []
     for _ in range(5):
-        r = await revert_pay_for_request(
-            test_key, integration_session, 500, snapshot
-        )
+        r = await revert_pay_for_request(test_key, integration_session, 500, snapshot)
         results.append(r)
 
     await integration_session.refresh(test_key)
diff --git a/tests/integration/test_temporary_balances_api.py b/tests/integration/test_temporary_balances_api.py
index feee0113..5439dcba 100644
--- a/tests/integration/test_temporary_balances_api.py
+++ b/tests/integration/test_temporary_balances_api.py
@@ -22,6 +22,7 @@ async def _add_key(
     hashed_key: str,
     *,
     balance: int = 0,
+    reserved_balance: int = 0,
     total_spent: int = 0,
     total_requests: int = 0,
     created_at: int | None = None,
@@ -31,6 +32,7 @@ async def _add_key(
     key = ApiKey(
         hashed_key=hashed_key,
         balance=balance,
+        reserved_balance=reserved_balance,
         total_spent=total_spent,
         total_requests=total_requests,
         parent_key_hash=parent_key_hash,
@@ -157,6 +159,41 @@ async def test_temporary_balances_totals_exclude_child_balance(
     assert totals["total_requests"] == 10
 
 
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_child_reservations_are_not_double_counted(
+    integration_client: httpx.AsyncClient,
+    integration_session: AsyncSession,
+) -> None:
+    await _add_key(
+        integration_session,
+        "parent",
+        balance=5_000,
+        reserved_balance=700,
+        created_at=1_000,
+    )
+    await _add_key(
+        integration_session,
+        "child",
+        reserved_balance=700,
+        parent_key_hash="parent",
+        created_at=1_001,
+    )
+
+    response = await integration_client.get(
+        "/admin/api/temporary-balances", headers=_admin_headers()
+    )
+
+    body = response.json()
+    rows = {row["hashed_key"]: row for row in body["balances"]}
+    assert rows["parent"]["available_balance"] == 4_300
+    assert rows["parent"]["reserved_balance"] == 700
+    assert rows["child"]["available_balance"] is None
+    assert rows["child"]["reserved_balance"] == 700
+    assert body["totals"]["total_reserved_balance"] == 700
+    assert body["totals"]["total_available_balance"] == 4_300
+
+
 @pytest.mark.integration
 @pytest.mark.asyncio
 async def test_temporary_balances_search_filters_total_and_totals(
diff --git a/tests/unit/test_cost_response_metadata.py b/tests/unit/test_cost_response_metadata.py
index beaf4005..3f06fac7 100644
--- a/tests/unit/test_cost_response_metadata.py
+++ b/tests/unit/test_cost_response_metadata.py
@@ -58,6 +58,7 @@ def _assert_cost_contract(response: Any) -> None:
         "input_msats": 1_200,
         "output_msats": 300,
         "total_msats": 1_500,
+        "charged_msats": 1_500,
         "total_usd": 0.0001,
         "cache_read_input_tokens": 8,
         "cache_creation_input_tokens": 2,
@@ -69,6 +70,36 @@ def _assert_cost_contract(response: Any) -> None:
     assert response.headers["X-Routstr-Output-Cost-Msats"] == "300"
 
 
+@pytest.mark.asyncio
+async def test_duplicate_finalization_publishes_zero_debit_and_computed_usage() -> None:
+    provider = _provider()
+    duplicate_cost = {**COST_DATA, "charged_msats": 0}
+    with patch(
+        "routstr.upstream.base.adjust_payment_for_tokens",
+        new=AsyncMock(return_value=duplicate_cost),
+    ):
+        response = await provider.handle_non_streaming_chat_completion(
+            _upstream_response(
+                {
+                    "model": "test-model",
+                    "usage": {"prompt_tokens": 10, "completion_tokens": 3},
+                }
+            ),
+            _key(),
+            _session(),
+            deducted_max_cost=10_000,
+        )
+
+    body = json.loads(response.body)
+    assert response.headers["X-Routstr-Cost-Msats"] == "0"
+    assert response.headers["X-Routstr-Computed-Cost-Msats"] == "1500"
+    assert body["usage"]["cost"]["total_msats"] == 0
+    assert body["usage"]["cost"]["charged_msats"] == 0
+    assert body["usage"]["cost"]["computed_msats"] == 1_500
+    assert body["cost"]["total_msats"] == 0
+    assert body["cost"]["computed_msats"] == 1_500
+
+
 @pytest.mark.asyncio
 async def test_balance_chat_completion_uses_shared_cost_contract() -> None:
     provider = _provider()
diff --git a/tests/unit/test_ehbp_finalize_payment.py b/tests/unit/test_ehbp_finalize_payment.py
index 08cb12ac..8f2c3bbb 100644
--- a/tests/unit/test_ehbp_finalize_payment.py
+++ b/tests/unit/test_ehbp_finalize_payment.py
@@ -6,12 +6,14 @@ from unittest.mock import AsyncMock, MagicMock
 import pytest
 from sqlalchemy.ext.asyncio import AsyncEngine, create_async_engine
 from sqlalchemy.pool import StaticPool
-from sqlmodel import SQLModel, select
+from sqlmodel import SQLModel, col, select, update
 from sqlmodel.ext.asyncio.session import AsyncSession
 
+import routstr.auth as auth_module
 from routstr.auth import get_reservation_snapshot, pay_for_request
 from routstr.core.db import ApiKey, ReservationRelease
 from routstr.upstream.ehbp import (
+    _inject_cost_response_headers,
     finalize_ehbp_actual_cost_payment,
     finalize_ehbp_max_cost_payment,
 )
@@ -26,7 +28,9 @@ def _make_engine() -> AsyncEngine:
 
 
 @pytest.fixture
-async def session(monkeypatch: pytest.MonkeyPatch) -> AsyncGenerator[AsyncSession, None]:
+async def session(
+    monkeypatch: pytest.MonkeyPatch,
+) -> AsyncGenerator[AsyncSession, None]:
     monkeypatch.setattr("routstr.upstream.ehbp.ROUTSTR_FEE_PERCENT", 0)
     engine = _make_engine()
     async with engine.begin() as conn:
@@ -35,6 +39,8 @@ async def session(monkeypatch: pytest.MonkeyPatch) -> AsyncGenerator[AsyncSessio
     try:
         yield db_session
     finally:
+        for release_id in list(auth_module._reservation_heartbeats):
+            await auth_module._stop_reservation_heartbeat(release_id)
         await db_session.close()
         await engine.dispose()
 
@@ -54,9 +60,7 @@ def _fail_nth_api_key_update(
     original_exec = session.exec
     api_key_updates = 0
 
-    async def exec_with_failure(
-        statement: Any, *args: Any, **kwargs: Any
-    ) -> Any:
+    async def exec_with_failure(statement: Any, *args: Any, **kwargs: Any) -> Any:
         nonlocal api_key_updates
         table = getattr(statement, "table", None)
         if getattr(table, "name", None) == "api_keys":
@@ -78,7 +82,7 @@ async def test_finalize_actual_cost_payment_updates_balance_and_releases_reserve
     await pay_for_request(key, 3_000, session)
     reservation = await get_reservation_snapshot(key, session)
 
-    await finalize_ehbp_actual_cost_payment(
+    charged = await finalize_ehbp_actual_cost_payment(
         key,
         session,
         reserved_cost_for_model=3_000,
@@ -93,6 +97,7 @@ async def test_finalize_actual_cost_payment_updates_balance_and_releases_reserve
         reservation_snapshot=reservation,
     )
 
+    assert charged == 1_200
     updated = await _api_key(session, "ehbp-actual")
     assert updated is not None
     assert updated.balance == 8_800
@@ -106,16 +111,14 @@ async def test_finalize_max_cost_payment_updates_parent_and_child_spend(
     session: AsyncSession,
 ) -> None:
     parent = ApiKey(hashed_key="ehbp-parent", balance=10_000)
-    child = ApiKey(
-        hashed_key="ehbp-child", balance=0, parent_key_hash="ehbp-parent"
-    )
+    child = ApiKey(hashed_key="ehbp-child", balance=0, parent_key_hash="ehbp-parent")
     session.add(parent)
     session.add(child)
     await session.commit()
     await pay_for_request(child, 3_000, session)
     reservation = await get_reservation_snapshot(child, session)
 
-    await finalize_ehbp_max_cost_payment(
+    charged = await finalize_ehbp_max_cost_payment(
         child,
         session,
         max_cost_for_model=3_000,
@@ -123,6 +126,7 @@ async def test_finalize_max_cost_payment_updates_parent_and_child_spend(
         reservation_snapshot=reservation,
     )
 
+    assert charged == 3_000
     updated_parent = await _api_key(session, "ehbp-parent")
     updated_child = await _api_key(session, "ehbp-child")
     assert updated_parent is not None
@@ -151,7 +155,7 @@ async def test_finalize_actual_cost_payment_rolls_back_when_parent_update_matche
     rollback_spy = AsyncMock(wraps=session.rollback)
     monkeypatch.setattr(session, "rollback", rollback_spy)
 
-    await finalize_ehbp_actual_cost_payment(
+    charged = await finalize_ehbp_actual_cost_payment(
         key,
         session,
         reserved_cost_for_model=3_000,
@@ -160,15 +164,17 @@ async def test_finalize_actual_cost_payment_rolls_back_when_parent_update_matche
         reservation_snapshot=reservation,
     )
 
+    assert charged == 0
     rollback_spy.assert_awaited_once()
     updated = await _api_key(session, "ehbp-missing-parent")
     assert updated is not None
     assert updated.balance == 10_000
-    assert updated.reserved_balance == 3_000
+    assert updated.reserved_balance == 0
     assert updated.total_spent == 0
     release = await session.get(ReservationRelease, reservation.release_id)
     assert release is not None
-    assert release.status == "active"
+    assert release.status == "released"
+    assert reservation.release_id not in auth_module._reservation_heartbeats
 
 
 @pytest.mark.asyncio
@@ -189,7 +195,7 @@ async def test_finalize_max_cost_payment_rolls_back_parent_when_child_update_mat
     reservation = await get_reservation_snapshot(child, session)
     _fail_nth_api_key_update(session, monkeypatch, target_update=2)
 
-    await finalize_ehbp_max_cost_payment(
+    charged = await finalize_ehbp_max_cost_payment(
         child,
         session,
         max_cost_for_model=3_000,
@@ -197,12 +203,84 @@ async def test_finalize_max_cost_payment_rolls_back_parent_when_child_update_mat
         reservation_snapshot=reservation,
     )
 
+    assert charged == 0
     updated_parent = await _api_key(session, "ehbp-rollback-parent")
     assert updated_parent is not None
     assert updated_parent.balance == 10_000
-    assert updated_parent.reserved_balance == 3_000
+    assert updated_parent.reserved_balance == 0
     assert updated_parent.total_spent == 0
     updated_child = await _api_key(session, "ehbp-missing-child")
     assert updated_child is not None
-    assert updated_child.reserved_balance == 3_000
+    assert updated_child.reserved_balance == 0
     assert updated_child.total_spent == 0
+    release = await session.get(ReservationRelease, reservation.release_id)
+    assert release is not None and release.status == "released"
+    assert reservation.release_id not in auth_module._reservation_heartbeats
+
+
+@pytest.mark.asyncio
+async def test_corrupt_child_aggregate_does_not_erase_parent_sibling_reserve(
+    session: AsyncSession,
+) -> None:
+    parent = ApiKey(hashed_key="ehbp-corrupt-parent", balance=10_000)
+    child = ApiKey(
+        hashed_key="ehbp-corrupt-child",
+        balance=0,
+        parent_key_hash=parent.hashed_key,
+    )
+    session.add(parent)
+    session.add(child)
+    await session.commit()
+    await pay_for_request(child, 3_000, session)
+    reservation = await get_reservation_snapshot(child, session)
+
+    await session.exec(  # type: ignore[call-overload]
+        update(ApiKey)
+        .where(col(ApiKey.hashed_key) == "ehbp-corrupt-parent")
+        .values(reserved_balance=5_000)
+    )
+    await session.exec(  # type: ignore[call-overload]
+        update(ApiKey)
+        .where(col(ApiKey.hashed_key) == "ehbp-corrupt-child")
+        .values(reserved_balance=1_000)
+    )
+    await session.commit()
+
+    charged = await finalize_ehbp_actual_cost_payment(
+        child,
+        session,
+        reserved_cost_for_model=3_000,
+        model_id="tinfoil/model",
+        cost_info={"total_msats": 1_200},
+        reservation_snapshot=reservation,
+    )
+
+    assert charged == 0
+    updated_parent = await _api_key(session, "ehbp-corrupt-parent")
+    updated_child = await _api_key(session, "ehbp-corrupt-child")
+    assert updated_parent is not None and updated_child is not None
+    assert updated_parent.balance == 10_000
+    assert updated_parent.reserved_balance == 5_000
+    assert updated_parent.total_spent == 0
+    assert updated_child.reserved_balance == 1_000
+    assert updated_child.total_spent == 0
+    release = await session.get(ReservationRelease, reservation.release_id)
+    assert release is not None and release.status == "released"
+    assert reservation.release_id not in auth_module._reservation_heartbeats
+
+
+def test_zero_debit_ehbp_headers_preserve_computed_cost() -> None:
+    headers: dict[str, str] = {}
+
+    _inject_cost_response_headers(
+        headers,
+        {
+            "total_msats": 0,
+            "computed_msats": 1_500,
+            "input_msats": 1_200,
+            "output_msats": 300,
+        },
+    )
+
+    assert headers["X-Routstr-Cost-Msats"] == "0"
+    assert headers["X-Routstr-Computed-Cost-Msats"] == "1500"
diff --git a/tests/unit/test_streaming_billing_finalization.py b/tests/unit/test_streaming_billing_finalization.py
index 2ae574ab..0e7a2ee9 100644
--- a/tests/unit/test_streaming_billing_finalization.py
+++ b/tests/unit/test_streaming_billing_finalization.py
@@ -1,4 +1,5 @@
 import asyncio
+import json
 from collections.abc import AsyncGenerator
 from unittest.mock import AsyncMock, MagicMock, patch
 
@@ -96,7 +97,10 @@ async def test_release_updates_parent_and_child_atomically() -> None:
 
 
 @pytest.mark.asyncio
-async def test_release_rolls_back_partial_parent_child_update() -> None:
+async def test_release_repairs_partial_parent_child_corruption() -> None:
+    """A child aggregate that no longer holds the reservation must not leave
+    the durable row active forever: the release rolls the subtraction back and
+    terminalizes the reservation without touching aggregates."""
     engine = await _engine()
     parent = ApiKey(hashed_key="parent", balance=1_000)
     child = ApiKey(hashed_key="child", parent_key_hash="parent", balance=0)
@@ -109,12 +113,13 @@ async def test_release_rolls_back_partial_parent_child_update() -> None:
         session.add(child)
         await session.commit()
 
-        assert await release_reservation(snapshot, session, 500) is False
+        assert await release_reservation(snapshot, session, 500) is True
         await session.refresh(parent)
         await session.refresh(child)
         record = await session.get(ReservationRelease, snapshot.release_id)
+        # Aggregates untouched — legacy cleanup reconciles them when stale.
         assert (parent.reserved_balance, child.reserved_balance) == (500, 100)
-        assert record is not None and record.status == "active"
+        assert record is not None and record.status == "released"
     await engine.dispose()
 
 
@@ -333,6 +338,73 @@ async def test_responses_streaming_releases_and_raises_on_billing_failure(
     release.assert_awaited_once_with(snapshot, session, 500)
 
 
+@pytest.mark.asyncio
+async def test_responses_streaming_duplicate_publishes_zero_settled_cost() -> None:
+    provider = BaseUpstreamProvider(
+        base_url="https://api.example.com", api_key="test-key"
+    )
+
+    async def aiter_bytes() -> AsyncGenerator[bytes, None]:
+        yield (
+            b'data: {"type":"response.completed","response":{"model":"test",'
+            b'"usage":{"input_tokens":2,"output_tokens":1}}}\n\n'
+        )
+        yield b"data: [DONE]\n\n"
+
+    upstream_response = MagicMock(
+        status_code=200,
+        headers={"content-type": "text/event-stream"},
+    )
+    upstream_response.aiter_bytes = aiter_bytes
+    key = MagicMock(spec=ApiKey)
+    key.hashed_key = "responses-duplicate"
+    key.balance = 10_000
+    session = MagicMock()
+    session.get = AsyncMock(return_value=key)
+    session_context = MagicMock()
+    session_context.__aenter__ = AsyncMock(return_value=session)
+    session_context.__aexit__ = AsyncMock(return_value=None)
+    cost_data = {
+        "input_tokens": 2,
+        "output_tokens": 1,
+        "input_msats": 1_000,
+        "output_msats": 500,
+        "total_msats": 1_500,
+        "charged_msats": 0,
+        "total_usd": 0.0001,
+    }
+
+    with (
+        patch(
+            "routstr.upstream.base.adjust_payment_for_tokens",
+            AsyncMock(return_value=cost_data),
+        ),
+        patch("routstr.upstream.base.create_session", return_value=session_context),
+    ):
+        response = await provider.handle_streaming_responses_completion(
+            response=upstream_response,
+            key=key,
+            max_cost_for_model=500,
+        )
+        chunks = [
+            chunk.decode() if isinstance(chunk, bytes) else chunk
+            async for chunk in response.body_iterator
+        ]
+
+    completed = next(
+        json.loads(line[6:])
+        for line in "".join(chunks).splitlines()
+        if line.startswith("data: {")
+    )
+    nested_usage = completed["response"]["usage"]
+    assert nested_usage["cost_sats"] == 0
+    assert nested_usage["cost"]["total_msats"] == 0
+    assert nested_usage["cost"]["charged_msats"] == 0
+    assert nested_usage["cost"]["computed_msats"] == 1_500
+    assert completed["cost"]["total_msats"] == 0
+    assert completed["cost"]["computed_msats"] == 1_500
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize("via_litellm", [False, True])
 @pytest.mark.parametrize(
diff --git a/ui/components/temporary-balances.tsx b/ui/components/temporary-balances.tsx
index 8370ef97..5d5f1d14 100644
--- a/ui/components/temporary-balances.tsx
+++ b/ui/components/temporary-balances.tsx
@@ -96,6 +96,8 @@ export function TemporaryBalances({
   const total = data?.total ?? 0;
   const totals = data?.totals ?? {
     total_balance: 0,
+    total_reserved_balance: 0,
+    total_available_balance: 0,
     total_spent: 0,
     total_requests: 0,
   };
@@ -180,7 +182,7 @@ export function TemporaryBalances({
               <Card>
                 <CardHeader className='flex flex-row items-center justify-between space-y-0 pb-2'>
                   <CardTitle className='text-muted-foreground text-sm font-medium'>
-                    Total Balance
+                    Total Available
                   </CardTitle>
                   <span className='inline-flex size-8 items-center justify-center'>
                     <DollarSign className='size-4 text-green-600 dark:text-green-300' />
@@ -188,7 +190,11 @@ export function TemporaryBalances({
                 </CardHeader>
                 <CardContent className='pt-0'>
                   <p className='text-2xl font-semibold tracking-tight tabular-nums'>
-                    {formatBalance(totals.total_balance)}
+                    {formatBalance(totals.total_available_balance)}
+                  </p>
+                  <p className='text-muted-foreground mt-1 text-xs'>
+                    {formatBalance(totals.total_balance)} raw ·{' '}
+                    {formatBalance(totals.total_reserved_balance)} reserved
                   </p>
                 </CardContent>
               </Card>
@@ -263,7 +269,7 @@ export function TemporaryBalances({
                     <TableHeader>
                       <TableRow>
                         <TableHead>Hashed Key</TableHead>
-                        <TableHead className='text-right'>Balance</TableHead>
+                        <TableHead className='text-right'>Available</TableHead>
                         <TableHead className='text-right'>
                           Total Spent
                         </TableHead>
@@ -284,7 +290,9 @@ export function TemporaryBalances({
                           <TableRow
                             key={`${balance.hashed_key}-${balance.parent_key_hash ?? 'root'}-${index}`}
                             className={cn(
-                              balance.balance === 0 && !isChild && 'opacity-60',
+                              balance.available_balance === 0 &&
+                                !isChild &&
+                                'opacity-60',
                               isChild && 'bg-muted/30'
                             )}
                           >
@@ -307,7 +315,19 @@ export function TemporaryBalances({
                                   (Parent)
                                 </span>
                               ) : (
-                                formatBalance(balance.balance)
+                                <div>
+                                  <div>
+                                    {formatBalance(
+                                      balance.available_balance ??
+                                        balance.balance
+                                    )}
+                                  </div>
+                                  <div className='text-muted-foreground text-xs'>
+                                    {formatBalance(balance.balance)} raw ·{' '}
+                                    {formatBalance(balance.reserved_balance)}{' '}
+                                    reserved
+                                  </div>
+                                </div>
                               )}
                             </TableCell>
                             <TableCell className='text-right font-mono'>
@@ -350,7 +370,9 @@ export function TemporaryBalances({
                       <Card
                         key={`${balance.hashed_key}-${balance.parent_key_hash ?? 'root'}-mobile-${index}`}
                         className={cn(
-                          balance.balance === 0 && !isChild && 'opacity-80',
+                          balance.available_balance === 0 &&
+                            !isChild &&
+                            'opacity-80',
                           isChild && 'bg-muted/30'
                         )}
                       >
@@ -372,13 +394,22 @@ export function TemporaryBalances({
                         <CardContent className='grid grid-cols-2 gap-3 p-4 pt-0'>
                           <div>
                             <p className='text-muted-foreground text-xs'>
-                              Balance
+                              Available
                             </p>
                             <p className='font-mono text-sm'>
                               {isChild
                                 ? '(Uses Parent)'
-                                : formatBalance(balance.balance)}
+                                : formatBalance(
+                                    balance.available_balance ?? balance.balance
+                                  )}
                             </p>
+                            {!isChild && (
+                              <p className='text-muted-foreground text-xs'>
+                                {formatBalance(balance.balance)} raw ·{' '}
+                                {formatBalance(balance.reserved_balance)}{' '}
+                                reserved
+                              </p>
+                            )}
                           </div>
                           <div>
                             <p className='text-muted-foreground text-xs'>
diff --git a/ui/lib/api/services/admin.ts b/ui/lib/api/services/admin.ts
index 7067627b..fd61e948 100644
--- a/ui/lib/api/services/admin.ts
+++ b/ui/lib/api/services/admin.ts
@@ -1082,6 +1082,8 @@ export interface CliTokenCreated {
 export const TemporaryBalanceSchema = z.object({
   hashed_key: z.string(),
   balance: z.number(),
+  reserved_balance: z.number(),
+  available_balance: z.number().nullable(),
   total_spent: z.number(),
   total_requests: z.number(),
   refund_address: z.string().nullable(),
@@ -1097,6 +1099,8 @@ export interface TemporaryBalancesResponse {
   total: number;
   totals: {
     total_balance: number;
+    total_reserved_balance: number;
+    total_available_balance: number;
     total_spent: number;
     total_requests: number;
   };