diff --git a/.env.example b/.env.example
index 8c3e2657..ba556919 100644
--- a/.env.example
+++ b/.env.example
@@ -22,13 +22,19 @@ ROUTSTR_SECRET_KEY=
 
 # Database
 # DATABASE_URL=sqlite+aiosqlite:///keys.db
-# Keep total pool capacity across all workers below the database connection limit.
+# Pool controls are validated at boot, sourced only from the environment, and
+# logged at startup. Defaults intentionally bound capacity and fail quickly so
+# leaked connections are visible instead of hidden by overflow connections.
+# Keep total capacity across all workers below the database connection limit.
 # DATABASE_POOL_SIZE=5
 # DATABASE_MAX_OVERFLOW=0
 # DATABASE_POOL_TIMEOUT=5
 # DATABASE_POOL_RECYCLE=1800
 # DATABASE_POOL_PRE_PING=true
+# Warn when a checkout is held this many seconds.
 # DATABASE_POOL_HOLD_WARN_SECONDS=10
+# SQLite serialises writes; increasing its pool can trade pool timeouts for
+# "database is locked" errors rather than increasing write throughput.
 
 # Node Information
 # NAME=My Routstr Node
@@ -40,6 +46,7 @@ ROUTSTR_SECRET_KEY=
 # CASHU_MINTS="https://mint.minibits.cash/Bitcoin,https://mint.cubabitcoin.org,https://ecashmint.otrta.me"
 # MINT_OPERATION_CONCURRENCY=4
 # RECEIVE_LN_ADDRESS=
+# REFUND_SWEEP_CLAIM_TIMEOUT_SECONDS=900
 
 # Custom Pricing Configuration
 # MODEL_BASED_PRICING=true
diff --git a/migrations/versions/8a1b2c3d4e5f_add_refund_sweep_claim_lease.py b/migrations/versions/8a1b2c3d4e5f_add_refund_sweep_claim_lease.py
new file mode 100644
index 00000000..f2964c26
--- /dev/null
+++ b/migrations/versions/8a1b2c3d4e5f_add_refund_sweep_claim_lease.py
@@ -0,0 +1,37 @@
+"""add recoverable refund sweep claim lease
+
+Revision ID: 8a1b2c3d4e5f
+Revises: 7f2843d3f4e4
+Create Date: 2026-07-24 23:15:00.000000
+"""
+
+import sqlalchemy as sa
+from alembic import op
+
+revision = "8a1b2c3d4e5f"
+down_revision = "7f2843d3f4e4"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    conn = op.get_bind()
+    columns = {
+        column["name"]
+        for column in sa.inspect(conn).get_columns("cashu_transactions")
+    }
+    if "sweep_started_at" not in columns:
+        op.add_column(
+            "cashu_transactions",
+            sa.Column("sweep_started_at", sa.Integer(), nullable=True),
+        )
+
+
+def downgrade() -> None:
+    conn = op.get_bind()
+    columns = {
+        column["name"]
+        for column in sa.inspect(conn).get_columns("cashu_transactions")
+    }
+    if "sweep_started_at" in columns:
+        op.drop_column("cashu_transactions", "sweep_started_at")
diff --git a/routstr/core/db.py b/routstr/core/db.py
index ab556cc5..0ee04933 100644
--- a/routstr/core/db.py
+++ b/routstr/core/db.py
@@ -15,6 +15,7 @@ from alembic.util.exc import CommandError
 from sqlalchemy import Index, UniqueConstraint, case, delete, event, or_
 from sqlalchemy.engine import make_url
 from sqlalchemy.exc import IntegrityError, OperationalError
+from sqlalchemy.ext.asyncio import AsyncEngine
 from sqlalchemy.ext.asyncio.engine import create_async_engine
 from sqlalchemy.orm import aliased
 from sqlmodel import Field, Relationship, SQLModel, col, func, select, update
@@ -27,58 +28,43 @@ logger = get_logger(__name__)
 DATABASE_URL = os.environ.get("DATABASE_URL", "sqlite+aiosqlite:///keys.db")
 
 
-def _env_bool(name: str, default: bool) -> bool:
-    raw = os.environ.get(name)
-    if raw is None:
-        return default
-    normalized = raw.strip().lower()
-    if normalized in {"1", "true", "yes", "on"}:
-        return True
-    if normalized in {"0", "false", "no", "off"}:
-        return False
-    raise ValueError(f"{name} must be a boolean")
+def create_db_engine(database_url: str = DATABASE_URL) -> AsyncEngine:
+    """Build an async engine from validated, environment-only pool settings."""
+    from .settings import settings
 
-
-def _engine_options(database_url: str) -> dict[str, int | float | bool]:
-    """Build a bounded pool configuration, preserving SQLite memory semantics."""
-    options: dict[str, int | float | bool] = {
-        "pool_pre_ping": _env_bool("DATABASE_POOL_PRE_PING", True)
-    }
     url = make_url(database_url)
     is_memory_sqlite = url.get_backend_name() == "sqlite" and url.database in {
         None,
         "",
         ":memory:",
     }
-    if is_memory_sqlite:
-        return options
+    options: dict[str, int | float | bool] = {
+        "pool_pre_ping": settings.database_pool_pre_ping,
+    }
+    if not is_memory_sqlite:
+        options.update(
+            pool_size=settings.database_pool_size,
+            max_overflow=settings.database_max_overflow,
+            pool_timeout=settings.database_pool_timeout,
+            pool_recycle=settings.database_pool_recycle,
+        )
 
-    pool_size = int(os.environ.get("DATABASE_POOL_SIZE", "5"))
-    max_overflow = int(os.environ.get("DATABASE_MAX_OVERFLOW", "0"))
-    pool_timeout = float(os.environ.get("DATABASE_POOL_TIMEOUT", "5"))
-    pool_recycle = int(os.environ.get("DATABASE_POOL_RECYCLE", "1800"))
-    if pool_size < 1:
-        raise ValueError("DATABASE_POOL_SIZE must be at least 1")
-    if max_overflow < 0:
-        raise ValueError("DATABASE_MAX_OVERFLOW cannot be negative")
-    if pool_timeout <= 0:
-        raise ValueError("DATABASE_POOL_TIMEOUT must be positive")
-    if pool_recycle < 0:
-        raise ValueError("DATABASE_POOL_RECYCLE cannot be negative")
-    options.update(
-        pool_size=pool_size,
-        max_overflow=max_overflow,
-        pool_timeout=pool_timeout,
-        pool_recycle=pool_recycle,
+    logger.info(
+        "Database pool configured",
+        extra={
+            "database_url_backend": url.get_backend_name(),
+            "in_memory_sqlite": is_memory_sqlite,
+            **options,
+        },
     )
-    return options
+    return create_async_engine(database_url, echo=False, **options)
 
 
-engine = create_async_engine(DATABASE_URL, echo=False, **_engine_options(DATABASE_URL))
+engine = create_db_engine()
 
-_POOL_HOLD_WARN_SECONDS = float(os.environ.get("DATABASE_POOL_HOLD_WARN_SECONDS", "10"))
-if _POOL_HOLD_WARN_SECONDS <= 0:
-    raise ValueError("DATABASE_POOL_HOLD_WARN_SECONDS must be positive")
+from .settings import settings as _runtime_settings  # noqa: E402
+
+_POOL_HOLD_WARN_SECONDS = _runtime_settings.database_pool_hold_warn_seconds
 
 
 @event.listens_for(engine.sync_engine, "checkout")
@@ -441,6 +427,10 @@ class CashuTransaction(SQLModel, table=True):  # type: ignore
     )
     collected: bool = Field(default=False)
     swept: bool = Field(default=False)
+    sweep_started_at: int | None = Field(
+        default=None,
+        description="Unix timestamp for a recoverable refund-sweep claim",
+    )
     source: str = Field(
         default="x-cashu",
         description="Payment source: x-cashu or apikey",
@@ -793,20 +783,12 @@ async def complete_routstr_fee_payout(
     return result.rowcount == 1
 
 
-async def balances_for_mint_and_unit(
-    db_session: AsyncSession, mint_url: str, unit: str
-) -> int:
-    query = select(func.sum(ApiKey.balance)).where(
-        ApiKey.refund_mint_url == mint_url, ApiKey.refund_currency == unit
-    )
-    result = await db_session.exec(query)
-    return result.one() or 0
-
-
 async def balances_by_mint_and_unit(
-    db_session: AsyncSession,
+    db_session: AsyncSession, mint_urls: list[str], units: list[str]
 ) -> dict[tuple[str, str], int]:
-    """Return all user liabilities in one query, grouped by mint and unit."""
+    """Return requested user liabilities grouped by mint and unit."""
+    if not mint_urls or not units:
+        return {}
     query = (
         select(
             col(ApiKey.refund_mint_url),
@@ -814,8 +796,8 @@ async def balances_by_mint_and_unit(
             func.sum(ApiKey.balance),
         )
         .where(
-            col(ApiKey.refund_mint_url).is_not(None),
-            col(ApiKey.refund_currency).is_not(None),
+            col(ApiKey.refund_mint_url).in_(mint_urls),
+            col(ApiKey.refund_currency).in_(units),
         )
         .group_by(col(ApiKey.refund_mint_url), col(ApiKey.refund_currency))
     )
diff --git a/routstr/core/settings.py b/routstr/core/settings.py
index 991c7554..34c6d9c1 100644
--- a/routstr/core/settings.py
+++ b/routstr/core/settings.py
@@ -102,6 +102,21 @@ class Settings(BaseSettings):
     enable_models_refresh: bool = Field(default=True, env="ENABLE_MODELS_REFRESH")
     refund_cache_ttl_seconds: int = Field(default=3600, env="REFUND_CACHE_TTL_SECONDS")
     refund_sweep_ttl_seconds: int = Field(default=604800, env="REFUND_SWEEP_TTL_SECONDS")
+    refund_sweep_claim_timeout_seconds: int = Field(
+        default=900, gt=0, env="REFUND_SWEEP_CLAIM_TIMEOUT_SECONDS"
+    )
+
+    # Database connection-pool controls (advanced). Keep the default pool
+    # bounded and fail quickly: increasing it can hide leaked connections and
+    # makes SQLite lock contention worse. These fields are env-only below.
+    database_pool_size: int = Field(default=5, ge=1, env="DATABASE_POOL_SIZE")
+    database_max_overflow: int = Field(default=0, ge=0, env="DATABASE_MAX_OVERFLOW")
+    database_pool_timeout: float = Field(default=5.0, gt=0, env="DATABASE_POOL_TIMEOUT")
+    database_pool_recycle: int = Field(default=1800, ge=0, env="DATABASE_POOL_RECYCLE")
+    database_pool_pre_ping: bool = Field(default=True, env="DATABASE_POOL_PRE_PING")
+    database_pool_hold_warn_seconds: float = Field(
+        default=10.0, gt=0, env="DATABASE_POOL_HOLD_WARN_SECONDS"
+    )
 
     # Logging
     log_level: str = Field(default="INFO", env="LOG_LEVEL")
@@ -147,10 +162,32 @@ def _normalize_settings_data(data: dict[str, Any]) -> dict[str, Any]:
 # ``routstr.core.vault``.
 SECRET_FIELDS = frozenset({"admin_password", "nsec"})
 
+# Infrastructure the node needs *before* it can open a DB session — so it can
+# never be configured from the DB (chicken-and-egg) and stays env-only. Unlike
+# secrets (owned by bootstrap), these are excluded so the DB settings blob can
+# neither store nor shadow them; env is always authoritative.
+ENV_ONLY_FIELDS = frozenset(
+    {
+        "database_pool_size",
+        "database_max_overflow",
+        "database_pool_timeout",
+        "database_pool_recycle",
+        "database_pool_pre_ping",
+        "database_pool_hold_warn_seconds",
+    }
+)
+
+_NON_PERSISTED_FIELDS = SECRET_FIELDS | ENV_ONLY_FIELDS
+
 
 def _strip_secret_fields(data: dict[str, Any]) -> dict[str, Any]:
-    """Return a copy of ``data`` without any secret fields (for persistence)."""
-    return {k: v for k, v in data.items() if k not in SECRET_FIELDS}
+    """Return a copy of ``data`` without secret or env-only fields.
+
+    Both are kept out of the persisted settings blob: secrets for confidentiality,
+    env-only fields (e.g. DB pool sizing) because they must never be sourced from
+    the database.
+    """
+    return {k: v for k, v in data.items() if k not in _NON_PERSISTED_FIELDS}
 
 
 def _apply_to_live_settings(data: dict[str, Any]) -> None:
@@ -330,7 +367,13 @@ class SettingsService:
             valid_fields = set(env_resolved.dict().keys())
             merged_dict: dict[str, Any] = dict(env_resolved.dict())
             merged_dict.update(
-                {k: v for k, v in db_json.items() if v not in (None, "", [], {}) and k in valid_fields}
+                {
+                    k: v
+                    for k, v in db_json.items()
+                    if v not in (None, "", [], {})
+                    and k in valid_fields
+                    and k not in ENV_ONLY_FIELDS
+                }
             )
             merged_dict = Settings(**merged_dict).dict()
 
@@ -397,8 +440,13 @@ class SettingsService:
                 )
             )
             await db_session.commit()
-            # Update in-place
+            # Update in-place. Env-only fields (e.g. DB pool sizing) are never
+            # applied here: the engine pool is already built at boot from env,
+            # so letting an update mutate the live value would only make it
+            # diverge from the running pool.
             for k, v in candidate.dict().items():
+                if k in ENV_ONLY_FIELDS:
+                    continue
                 setattr(settings, k, v)
             cls._current = settings
             return settings
diff --git a/routstr/wallet.py b/routstr/wallet.py
index d61bbd4c..ac2fda3d 100644
--- a/routstr/wallet.py
+++ b/routstr/wallet.py
@@ -836,8 +836,22 @@ async def fetch_all_balances(
     if units is None:
         units = ["sat", "msat"]
 
-    async with db.create_session() as session:
-        user_balances = await db.balances_by_mint_and_unit(session)
+    # Received tokens are stored against primary_mint even when cashu_mints is
+    # empty, so include it in both the liability query and mint fan-out.
+    mint_urls: list[str] = list(settings.cashu_mints)
+    if settings.primary_mint and settings.primary_mint not in mint_urls:
+        mint_urls.append(settings.primary_mint)
+
+    user_balances: dict[tuple[str, str], int] = {}
+    liabilities_error: str | None = None
+    try:
+        async with db.create_session() as session:
+            user_balances = await db.balances_by_mint_and_unit(
+                session, mint_urls, units
+            )
+    except Exception as e:
+        logger.error("Error reading user balances", extra={"error": str(e)})
+        liabilities_error = str(e)
 
     mint_check_limit = asyncio.Semaphore(settings.mint_operation_concurrency)
 
@@ -874,40 +888,37 @@ async def fetch_all_balances(
             }
             return error_result
 
-    # Build the set of mints to inspect. Received tokens are stored against
-    # ``primary_mint`` (which defaults to a real mint even when ``cashu_mints``
-    # is empty), so include it as a fallback — otherwise a node that accepts
-    # payments would still report empty balances when ``cashu_mints`` is unset.
-    mint_urls: list[str] = list(settings.cashu_mints)
-    if settings.primary_mint and settings.primary_mint not in mint_urls:
-        mint_urls.append(settings.primary_mint)
-
     tasks = [fetch_balance(mint_url, unit) for mint_url in mint_urls for unit in units]
     balance_details = list(await asyncio.gather(*tasks))
 
-    # Calculate totals
     total_wallet_balance_sats = 0
     total_user_balance_sats = 0
-
     for detail in balance_details:
-        if not detail.get("error"):
-            # Convert to sats for total calculation
-            unit = detail["unit"]
-            proofs_balance_sats = (
-                detail["wallet_balance"]
-                if unit == "sat"
-                else detail["wallet_balance"] // 1000
-            )
-            user_balance_sats = (
+        if detail.get("error"):
+            continue
+        unit = detail["unit"]
+        total_wallet_balance_sats += (
+            detail["wallet_balance"]
+            if unit == "sat"
+            else detail["wallet_balance"] // 1000
+        )
+        if liabilities_error is None:
+            total_user_balance_sats += (
                 detail["user_balance"]
                 if unit == "sat"
                 else detail["user_balance"] // 1000
             )
 
-            total_wallet_balance_sats += proofs_balance_sats
-            total_user_balance_sats += user_balance_sats
-
-    owner_balance = total_wallet_balance_sats - total_user_balance_sats
+    if liabilities_error is None:
+        owner_balance = total_wallet_balance_sats - total_user_balance_sats
+    else:
+        # Custody remains knowable when the DB read fails, but the user/owner
+        # split does not. Never report unknown liabilities as owner profit.
+        owner_balance = 0
+        for detail in balance_details:
+            detail["user_balance"] = 0
+            detail["owner_balance"] = 0
+            detail.setdefault("error", liabilities_error)
 
     return (
         balance_details,
@@ -947,9 +958,10 @@ async def periodic_payout() -> None:
                         # the liability, shrinking the payout — never sending
                         # customer-backed funds as profit.
                         async with db.create_session() as session:
-                            user_balance = await db.balances_for_mint_and_unit(
-                                session, mint_url, unit
+                            balances = await db.balances_by_mint_and_unit(
+                                session, [mint_url], [unit]
                             )
+                        user_balance = balances.get((mint_url, unit), 0)
                         if unit == "sat":
                             user_balance = user_balance // 1000
                         proofs_balance = sum(proof.amount for proof in proofs)
@@ -993,20 +1005,37 @@ async def periodic_payout() -> None:
             )
 
 
+async def _set_refund_sweep_state(refund_id: str, **values: object) -> None:
+    async with db.create_session() as session:
+        await session.exec(  # type: ignore[call-overload]
+            update(db.CashuTransaction)
+            .where(col(db.CashuTransaction.id) == refund_id)
+            .values(**values)
+        )
+        await session.commit()
+
+
 async def _refund_sweep_once(cutoff: int) -> None:
+    claim_cutoff = (
+        int(time.time()) - settings.refund_sweep_claim_timeout_seconds
+    )
+    claim_available = col(db.CashuTransaction.sweep_started_at).is_(None) | (
+        col(db.CashuTransaction.sweep_started_at) < claim_cutoff
+    )
     async with db.create_session() as session:
         stmt = select(db.CashuTransaction).where(
             db.CashuTransaction.type == "out",
             db.CashuTransaction.collected == False,  # noqa: E712
             db.CashuTransaction.swept == False,  # noqa: E712
             db.CashuTransaction.created_at < cutoff,
+            claim_available,
         )
         results = await session.exec(stmt)
         refunds = results.all()
 
     for refund in refunds:
-        # Claim the refund atomically before redeeming so a concurrent sweep
-        # cannot redeem the same token and misreport it as client-collected.
+        reclaimed_stale_claim = refund.sweep_started_at is not None
+        claim_started_at = int(time.time())
         async with db.create_session() as session:
             claim = await session.exec(  # type: ignore[call-overload]
                 update(db.CashuTransaction)
@@ -1014,8 +1043,9 @@ async def _refund_sweep_once(cutoff: int) -> None:
                     col(db.CashuTransaction.id) == refund.id,
                     col(db.CashuTransaction.swept) == False,  # noqa: E712
                     col(db.CashuTransaction.collected) == False,  # noqa: E712
+                    claim_available,
                 )
-                .values(swept=True)
+                .values(sweep_started_at=claim_started_at)
             )
             await session.commit()
         if claim.rowcount != 1:
@@ -1023,6 +1053,9 @@ async def _refund_sweep_once(cutoff: int) -> None:
 
         try:
             await recieve_token(refund.token)
+            await _set_refund_sweep_state(
+                refund.id, swept=True, sweep_started_at=None
+            )
             logger.info(
                 "Swept uncollected refund",
                 extra={
@@ -1031,38 +1064,42 @@ async def _refund_sweep_once(cutoff: int) -> None:
                     "unit": refund.unit,
                 },
             )
-        except Exception as e:
+        except BaseException as e:
             error_msg = str(e).lower()
-            if "already spent" in error_msg:
-                # We held the claim, so nobody else swept it: the client
-                # really collected the token.
-                async with db.create_session() as session:
-                    await session.exec(  # type: ignore[call-overload]
-                        update(db.CashuTransaction)
-                        .where(col(db.CashuTransaction.id) == refund.id)
-                        .values(collected=True, swept=False)
+            if isinstance(e, Exception) and "already spent" in error_msg:
+                if reclaimed_stale_claim:
+                    # A prior worker may have redeemed the token and crashed
+                    # before finalizing. Treat the ambiguous stale claim as a
+                    # completed sweep rather than misreporting client collection.
+                    await _set_refund_sweep_state(
+                        refund.id, swept=True, sweep_started_at=None
+                    )
+                else:
+                    await _set_refund_sweep_state(
+                        refund.id,
+                        collected=True,
+                        swept=False,
+                        sweep_started_at=None,
                     )
-                    await session.commit()
                 logger.info(
-                    "Refund already spent (client collected), marking swept",
-                    extra={"id": refund.id},
-                )
-            else:
-                # Release the claim so the next sweep retries this refund.
-                async with db.create_session() as session:
-                    await session.exec(  # type: ignore[call-overload]
-                        update(db.CashuTransaction)
-                        .where(col(db.CashuTransaction.id) == refund.id)
-                        .values(swept=False)
-                    )
-                    await session.commit()
-                logger.warning(
-                    "Failed to sweep refund",
+                    "Refund token was already spent",
                     extra={
                         "id": refund.id,
-                        "error": str(e),
+                        "reclaimed_stale_claim": reclaimed_stale_claim,
                     },
                 )
+            else:
+                # Cancellation is a known-no-send outcome at this boundary, so
+                # release the lease under shield and let a later sweep retry.
+                await asyncio.shield(
+                    _set_refund_sweep_state(refund.id, sweep_started_at=None)
+                )
+                if not isinstance(e, Exception):
+                    raise
+                logger.warning(
+                    "Failed to sweep refund",
+                    extra={"id": refund.id, "error": str(e)},
+                )
 
 
 async def refund_sweep_once() -> None:
@@ -1112,15 +1149,21 @@ async def periodic_routstr_fee_payout() -> None:
                 if accumulated_sats < ROUTSTR_FEE_DEFAULT_PAYOUT:
                     continue
                 paid_msats = accumulated_sats * 1000
-                payout_checkpointed = await db.reset_routstr_fee(session, paid_msats)
-                if not payout_checkpointed:
-                    logger.warning("Routstr fee payout was already claimed")
-                    continue
 
+            # Wallet/proof preparation cannot send funds, so do it before the
+            # durable checkpoint. A preparation failure must not strand an
+            # in-progress payout that requires manual reconciliation.
             wallet = await get_wallet(settings.primary_mint, "sat")
             proofs = get_proofs_per_mint_and_unit(
                 wallet, settings.primary_mint, "sat", not_reserved=True
             )
+
+            async with db.create_session() as session:
+                payout_checkpointed = await db.reset_routstr_fee(session, paid_msats)
+            if not payout_checkpointed:
+                logger.warning("Routstr fee payout was already claimed")
+                continue
+
             try:
                 amount_received = await raw_send_to_lnurl(
                     wallet,
diff --git a/tests/unit/test_balances_by_mint_and_unit.py b/tests/unit/test_balances_by_mint_and_unit.py
new file mode 100644
index 00000000..bb1b3c81
--- /dev/null
+++ b/tests/unit/test_balances_by_mint_and_unit.py
@@ -0,0 +1,100 @@
+"""Real-DB coverage for db.balances_by_mint_and_unit.
+
+Verifies the grouped liability query used by fetch_all_balances: it sums
+balances per (mint_url, unit), filters to the requested mints/units, excludes
+NULL mint/currency rows, and returns nothing for empty inputs.
+"""
+
+from typing import AsyncGenerator
+
+import pytest
+from sqlalchemy.ext.asyncio import AsyncEngine, create_async_engine
+from sqlalchemy.pool import StaticPool
+from sqlmodel import SQLModel
+from sqlmodel.ext.asyncio.session import AsyncSession
+
+from routstr.core.db import ApiKey, balances_by_mint_and_unit
+
+
+def _make_engine() -> AsyncEngine:
+    return create_async_engine(
+        "sqlite+aiosqlite://",
+        poolclass=StaticPool,
+        connect_args={"check_same_thread": False},
+    )
+
+
+@pytest.fixture
+async def session() -> "AsyncGenerator[AsyncSession, None]":
+    engine = _make_engine()
+    async with engine.begin() as conn:
+        await conn.run_sync(SQLModel.metadata.create_all)
+    db_session = AsyncSession(engine, expire_on_commit=False)
+    try:
+        yield db_session
+    finally:
+        await db_session.close()
+        await engine.dispose()
+
+
+async def _add_key(
+    session: AsyncSession,
+    hashed_key: str,
+    balance: int,
+    mint_url: str | None,
+    currency: str | None,
+) -> None:
+    session.add(
+        ApiKey(
+            hashed_key=hashed_key,
+            balance=balance,
+            refund_mint_url=mint_url,
+            refund_currency=currency,
+        )
+    )
+    await session.commit()
+
+
+@pytest.mark.asyncio
+async def test_sums_and_groups_by_mint_and_unit(session: AsyncSession) -> None:
+    await _add_key(session, "a", 1000, "http://m1", "sat")
+    await _add_key(session, "b", 500, "http://m1", "sat")
+    await _add_key(session, "c", 7000, "http://m1", "msat")
+    await _add_key(session, "d", 200, "http://m2", "sat")
+
+    result = await balances_by_mint_and_unit(
+        session, ["http://m1", "http://m2"], ["sat", "msat"]
+    )
+
+    assert result[("http://m1", "sat")] == 1500
+    assert result[("http://m1", "msat")] == 7000
+    assert result[("http://m2", "sat")] == 200
+
+
+@pytest.mark.asyncio
+async def test_filters_out_unrequested_mints_and_units(session: AsyncSession) -> None:
+    await _add_key(session, "a", 1000, "http://wanted", "sat")
+    await _add_key(session, "b", 999, "http://other", "sat")
+    await _add_key(session, "c", 888, "http://wanted", "usd")
+
+    result = await balances_by_mint_and_unit(session, ["http://wanted"], ["sat"])
+
+    assert result == {("http://wanted", "sat"): 1000}
+
+
+@pytest.mark.asyncio
+async def test_excludes_rows_with_null_mint_or_currency(session: AsyncSession) -> None:
+    await _add_key(session, "a", 1000, "http://m1", "sat")
+    await _add_key(session, "b", 4242, None, None)
+
+    result = await balances_by_mint_and_unit(session, ["http://m1"], ["sat"])
+
+    assert result == {("http://m1", "sat"): 1000}
+
+
+@pytest.mark.asyncio
+async def test_empty_inputs_return_empty_mapping(session: AsyncSession) -> None:
+    await _add_key(session, "a", 1000, "http://m1", "sat")
+
+    assert await balances_by_mint_and_unit(session, [], ["sat"]) == {}
+    assert await balances_by_mint_and_unit(session, ["http://m1"], []) == {}
diff --git a/tests/unit/test_db_pool_config.py b/tests/unit/test_db_pool_config.py
index ccfba575..a2838621 100644
--- a/tests/unit/test_db_pool_config.py
+++ b/tests/unit/test_db_pool_config.py
@@ -2,63 +2,45 @@ from types import SimpleNamespace
 from unittest.mock import MagicMock, patch
 
 import pytest
+from sqlalchemy.pool import StaticPool
 
 from routstr.core import db
-from routstr.core.db import _engine_options
+from routstr.core.db import create_db_engine
+from routstr.core.settings import settings
 
 
-def test_engine_options_use_bounded_fail_fast_pool(monkeypatch) -> None:  # type: ignore[no-untyped-def]
-    monkeypatch.delenv("DATABASE_POOL_SIZE", raising=False)
-    monkeypatch.delenv("DATABASE_MAX_OVERFLOW", raising=False)
-    monkeypatch.delenv("DATABASE_POOL_TIMEOUT", raising=False)
-    monkeypatch.delenv("DATABASE_POOL_RECYCLE", raising=False)
-    monkeypatch.delenv("DATABASE_POOL_PRE_PING", raising=False)
-
-    options = _engine_options("postgresql+asyncpg://db/routstr")
-
-    assert options == {
-        "pool_size": 5,
-        "max_overflow": 0,
-        "pool_timeout": 5.0,
-        "pool_recycle": 1800,
-        "pool_pre_ping": True,
-    }
-
-
-def test_engine_options_are_operator_configurable(monkeypatch) -> None:  # type: ignore[no-untyped-def]
-    monkeypatch.setenv("DATABASE_POOL_SIZE", "12")
-    monkeypatch.setenv("DATABASE_MAX_OVERFLOW", "3")
-    monkeypatch.setenv("DATABASE_POOL_TIMEOUT", "2.5")
-    monkeypatch.setenv("DATABASE_POOL_RECYCLE", "900")
-    monkeypatch.setenv("DATABASE_POOL_PRE_PING", "false")
-
-    assert _engine_options("sqlite+aiosqlite:///keys.db") == {
-        "pool_size": 12,
-        "max_overflow": 3,
-        "pool_timeout": 2.5,
-        "pool_recycle": 900,
-        "pool_pre_ping": False,
-    }
-
-
-@pytest.mark.parametrize(
-    ("name", "value"),
-    [
-        ("DATABASE_POOL_SIZE", "0"),
-        ("DATABASE_MAX_OVERFLOW", "-1"),
-        ("DATABASE_POOL_TIMEOUT", "0"),
-        ("DATABASE_POOL_RECYCLE", "-1"),
-        ("DATABASE_POOL_PRE_PING", "maybe"),
-    ],
-)
-def test_engine_options_reject_invalid_values(
-    monkeypatch: pytest.MonkeyPatch,
-    name: str,
-    value: str,
+@pytest.mark.asyncio
+async def test_engine_uses_validated_bounded_pool_settings(
+    monkeypatch: pytest.MonkeyPatch, tmp_path: object
 ) -> None:
-    monkeypatch.setenv(name, value)
-    with pytest.raises(ValueError):
-        _engine_options("postgresql+asyncpg://db/routstr")
+    monkeypatch.setattr(settings, "database_pool_size", 12)
+    monkeypatch.setattr(settings, "database_max_overflow", 3)
+    monkeypatch.setattr(settings, "database_pool_timeout", 2.5)
+    monkeypatch.setattr(settings, "database_pool_recycle", 900)
+    monkeypatch.setattr(settings, "database_pool_pre_ping", False)
+
+    engine = create_db_engine(f"sqlite+aiosqlite:///{tmp_path}/pool.db")
+    try:
+        assert engine.pool.size() == 12  # type: ignore[attr-defined]
+        assert engine.pool._max_overflow == 3  # type: ignore[attr-defined]
+        assert engine.pool._timeout == 2.5  # type: ignore[attr-defined]
+        assert engine.pool._recycle == 900
+        assert engine.pool._pre_ping is False
+    finally:
+        await engine.dispose()
+
+
+@pytest.mark.asyncio
+async def test_memory_sqlite_keeps_static_pool(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setattr(settings, "database_pool_pre_ping", True)
+    engine = create_db_engine("sqlite+aiosqlite://")
+    try:
+        assert isinstance(engine.pool, StaticPool)
+        assert engine.pool._pre_ping is True
+    finally:
+        await engine.dispose()
 
 
 def test_pool_observer_warns_when_connection_is_held_too_long(
@@ -75,9 +57,3 @@ def test_pool_observer_warns_when_connection_is_held_too_long(
 
     warning.assert_called_once()
     assert warning.call_args.kwargs["extra"]["held_seconds"] == 12.5
-
-
-def test_memory_sqlite_keeps_dialect_static_pool(monkeypatch) -> None:  # type: ignore[no-untyped-def]
-    monkeypatch.delenv("DATABASE_POOL_PRE_PING", raising=False)
-
-    assert _engine_options("sqlite+aiosqlite://") == {"pool_pre_ping": True}
diff --git a/tests/unit/test_fee_payout_crash_safety.py b/tests/unit/test_fee_payout_crash_safety.py
index 19b95ec3..7a0cd94a 100644
--- a/tests/unit/test_fee_payout_crash_safety.py
+++ b/tests/unit/test_fee_payout_crash_safety.py
@@ -57,7 +57,7 @@ async def test_fee_payout_checkpoint_is_atomic_and_durable() -> None:
 
 
 @pytest.mark.asyncio
-async def test_fee_payout_checkpoints_before_sending() -> None:
+async def test_fee_payout_prepares_wallet_then_checkpoints_before_sending() -> None:
     session = Mock()
     fee = SimpleNamespace(
         accumulated_msats=5_000,
@@ -67,6 +67,10 @@ async def test_fee_payout_checkpoints_before_sending() -> None:
     payout_wallet = Mock()
     events: list[str] = []
 
+    async def prepare(*_args: object) -> Mock:
+        events.append("prepare")
+        return payout_wallet
+
     async def checkpoint(*_args: object) -> bool:
         events.append("checkpoint")
         return True
@@ -93,14 +97,86 @@ async def test_fee_payout_checkpoints_before_sending() -> None:
         patch("routstr.wallet.db.get_routstr_fee", AsyncMock(return_value=fee)),
         patch("routstr.wallet.db.reset_routstr_fee", side_effect=checkpoint),
         patch("routstr.wallet.db.complete_routstr_fee_payout", side_effect=complete),
-        patch("routstr.wallet.get_wallet", AsyncMock(return_value=payout_wallet)),
+        patch("routstr.wallet.get_wallet", AsyncMock(side_effect=prepare)),
         patch("routstr.wallet.get_proofs_per_mint_and_unit", return_value=[]),
         patch("routstr.wallet.raw_send_to_lnurl", side_effect=send),
     ):
         with pytest.raises(asyncio.CancelledError):
             await wallet.periodic_routstr_fee_payout()
 
-    assert events == ["checkpoint", "send", "complete"]
+    assert events == ["prepare", "checkpoint", "send", "complete"]
+
+
+@pytest.mark.asyncio
+async def test_fee_payout_preparation_failure_does_not_checkpoint() -> None:
+    session = Mock()
+    fee = SimpleNamespace(
+        accumulated_msats=5_000,
+        payout_in_progress_msats=0,
+        payout_started_at=None,
+    )
+    checkpoint = AsyncMock()
+
+    with (
+        patch("routstr.auth.ROUTSTR_FEE_DEFAULT_PAYOUT", 1),
+        patch("routstr.auth.ROUTSTR_FEE_PAYOUT_INTERVAL_SECONDS", 1),
+        patch("routstr.auth.ROUTSTR_LN_ADDRESS", "fees@example.com"),
+        patch(
+            "routstr.wallet.asyncio.sleep",
+            AsyncMock(side_effect=[None, asyncio.CancelledError()]),
+        ),
+        patch(
+            "routstr.wallet.db.create_session", return_value=_session_context(session)
+        ),
+        patch("routstr.wallet.db.get_routstr_fee", AsyncMock(return_value=fee)),
+        patch("routstr.wallet.db.reset_routstr_fee", checkpoint),
+        patch(
+            "routstr.wallet.get_wallet",
+            AsyncMock(side_effect=RuntimeError("wallet unavailable")),
+        ),
+    ):
+        with pytest.raises(asyncio.CancelledError):
+            await wallet.periodic_routstr_fee_payout()
+
+    checkpoint.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_fee_payout_lost_checkpoint_race_does_not_send() -> None:
+    session = Mock()
+    fee = SimpleNamespace(
+        accumulated_msats=5_000,
+        payout_in_progress_msats=0,
+        payout_started_at=None,
+    )
+    send = AsyncMock()
+
+    with (
+        patch("routstr.auth.ROUTSTR_FEE_DEFAULT_PAYOUT", 1),
+        patch("routstr.auth.ROUTSTR_FEE_PAYOUT_INTERVAL_SECONDS", 1),
+        patch("routstr.auth.ROUTSTR_LN_ADDRESS", "fees@example.com"),
+        patch(
+            "routstr.wallet.asyncio.sleep",
+            AsyncMock(side_effect=[None, asyncio.CancelledError()]),
+        ),
+        patch(
+            "routstr.wallet.db.create_session", return_value=_session_context(session)
+        ),
+        patch("routstr.wallet.db.get_routstr_fee", AsyncMock(return_value=fee)),
+        patch(
+            "routstr.wallet.db.reset_routstr_fee",
+            AsyncMock(return_value=False),
+        ),
+        patch("routstr.wallet.get_wallet", AsyncMock(return_value=Mock())),
+        patch("routstr.wallet.get_proofs_per_mint_and_unit", return_value=[]),
+        patch("routstr.wallet.raw_send_to_lnurl", send),
+        patch("routstr.wallet.logger.warning") as warning,
+    ):
+        with pytest.raises(asyncio.CancelledError):
+            await wallet.periodic_routstr_fee_payout()
+
+    send.assert_not_awaited()
+    warning.assert_called_once_with("Routstr fee payout was already claimed")
 
 
 @pytest.mark.asyncio
diff --git a/tests/unit/test_fetch_all_balances.py b/tests/unit/test_fetch_all_balances.py
index 1d69e31e..3427cf78 100644
--- a/tests/unit/test_fetch_all_balances.py
+++ b/tests/unit/test_fetch_all_balances.py
@@ -254,3 +254,58 @@ async def test_fetch_all_balances_no_duplicate_primary_mint() -> None:
 
     assert [d["mint_url"] for d in details] == ["http://primary:3338"]
     assert total_wallet == 1000
+
+
+@pytest.mark.asyncio
+async def test_fetch_all_balances_degrades_when_liability_read_fails() -> None:
+    from routstr.core.settings import settings
+
+    with (
+        patch.object(settings, "cashu_mints", []),
+        patch.object(settings, "primary_mint", "http://primary:3338"),
+        patch("routstr.wallet.db.create_session", _fake_session),
+        patch(
+            "routstr.wallet.db.balances_by_mint_and_unit",
+            AsyncMock(side_effect=RuntimeError("db pool exhausted")),
+        ),
+        patch("routstr.wallet.get_wallet", AsyncMock(return_value=MagicMock())),
+        patch(
+            "routstr.wallet.get_proofs_per_mint_and_unit",
+            MagicMock(return_value=[MagicMock(amount=1000)]),
+        ),
+        patch(
+            "routstr.wallet.slow_filter_spend_proofs",
+            AsyncMock(side_effect=lambda proofs, wallet: proofs),
+        ),
+    ):
+        details, total_wallet, total_user, owner = await fetch_all_balances(
+            units=["sat"]
+        )
+
+    assert details[0]["error"] == "db pool exhausted"
+    assert details[0]["wallet_balance"] == 1000
+    assert details[0]["user_balance"] == 0
+    assert details[0]["owner_balance"] == 0
+    assert (total_wallet, total_user, owner) == (1000, 0, 0)
+
+
+@pytest.mark.asyncio
+async def test_liability_error_keeps_more_specific_mint_error() -> None:
+    from routstr.core.settings import settings
+
+    with (
+        patch.object(settings, "cashu_mints", []),
+        patch.object(settings, "primary_mint", "http://primary:3338"),
+        patch("routstr.wallet.db.create_session", _fake_session),
+        patch(
+            "routstr.wallet.db.balances_by_mint_and_unit",
+            AsyncMock(side_effect=RuntimeError("db pool exhausted")),
+        ),
+        patch(
+            "routstr.wallet.get_wallet",
+            AsyncMock(side_effect=RuntimeError("mint down")),
+        ),
+    ):
+        details, *_ = await fetch_all_balances(units=["sat"])
+
+    assert details[0]["error"] == "mint down"
diff --git a/tests/unit/test_periodic_payout.py b/tests/unit/test_periodic_payout.py
index c1768dc7..69d13ee8 100644
--- a/tests/unit/test_periodic_payout.py
+++ b/tests/unit/test_periodic_payout.py
@@ -77,7 +77,8 @@ async def test_periodic_payout_includes_primary_mint_not_in_cashu_mints() -> Non
             AsyncMock(side_effect=lambda proofs, wallet: proofs),
         ),
         patch(
-            "routstr.wallet.db.balances_for_mint_and_unit", AsyncMock(return_value=0)
+            "routstr.wallet.db.balances_by_mint_and_unit",
+            AsyncMock(return_value={}),
         ),
         patch("routstr.wallet.raw_send_to_lnurl", raw_send),
     ):
@@ -130,8 +131,8 @@ async def test_periodic_payout_releases_session_before_slow_mint_send() -> None:
             AsyncMock(side_effect=lambda proofs, wallet: proofs),
         ),
         patch(
-            "routstr.wallet.db.balances_for_mint_and_unit",
-            AsyncMock(return_value=0),
+            "routstr.wallet.db.balances_by_mint_and_unit",
+            AsyncMock(return_value={}),
         ),
         patch("routstr.wallet.raw_send_to_lnurl", AsyncMock(side_effect=raw_send)),
     ):
@@ -172,7 +173,8 @@ async def test_periodic_payout_isolates_failing_mint() -> None:
             AsyncMock(side_effect=lambda proofs, wallet: proofs),
         ),
         patch(
-            "routstr.wallet.db.balances_for_mint_and_unit", AsyncMock(return_value=0)
+            "routstr.wallet.db.balances_by_mint_and_unit",
+            AsyncMock(return_value={}),
         ),
         patch("routstr.wallet.raw_send_to_lnurl", raw_send),
     ):
diff --git a/tests/unit/test_refund_sweep.py b/tests/unit/test_refund_sweep.py
index 64b36efc..3a8a68e2 100644
--- a/tests/unit/test_refund_sweep.py
+++ b/tests/unit/test_refund_sweep.py
@@ -1,3 +1,4 @@
+import asyncio
 from collections.abc import AsyncIterator
 from contextlib import asynccontextmanager
 from pathlib import Path
@@ -154,3 +155,73 @@ async def test_refund_sweep_records_terminal_but_not_transient_failures(
     refund = (await _load(session_factory))["refund"]
     assert refund.collected is collected
     assert refund.swept is False
+    assert refund.sweep_started_at is None
+
+
+@pytest.mark.asyncio
+async def test_refund_sweep_releases_claim_on_cancellation(
+    session_factory: async_sessionmaker[AsyncSession],
+) -> None:
+    await _insert(
+        session_factory,
+        CashuTransaction(
+            token="cancelled", amount=1, unit="sat", type="out", created_at=800
+        ),
+    )
+    with (
+        patch("routstr.wallet.db.create_session", side_effect=session_factory),
+        patch("routstr.wallet.settings.refund_sweep_ttl_seconds", 100),
+        patch("routstr.wallet.time.time", return_value=1000),
+        patch(
+            "routstr.wallet.recieve_token",
+            AsyncMock(side_effect=asyncio.CancelledError()),
+        ),
+    ):
+        with pytest.raises(asyncio.CancelledError):
+            await refund_sweep_once()
+
+    refund = (await _load(session_factory))["cancelled"]
+    assert refund.swept is False
+    assert refund.sweep_started_at is None
+
+
+@pytest.mark.asyncio
+async def test_refund_sweep_recovers_stale_claim_without_misreporting_collection(
+    session_factory: async_sessionmaker[AsyncSession],
+) -> None:
+    await _insert(
+        session_factory,
+        CashuTransaction(
+            token="stale",
+            amount=1,
+            unit="sat",
+            type="out",
+            created_at=800,
+            sweep_started_at=100,
+        ),
+        CashuTransaction(
+            token="active",
+            amount=1,
+            unit="sat",
+            type="out",
+            created_at=800,
+            sweep_started_at=950,
+        ),
+    )
+    receive = AsyncMock(side_effect=RuntimeError("token already spent"))
+    with (
+        patch("routstr.wallet.db.create_session", side_effect=session_factory),
+        patch("routstr.wallet.settings.refund_sweep_ttl_seconds", 100),
+        patch("routstr.wallet.settings.refund_sweep_claim_timeout_seconds", 200),
+        patch("routstr.wallet.time.time", return_value=1000),
+        patch("routstr.wallet.recieve_token", receive),
+    ):
+        await refund_sweep_once()
+
+    receive.assert_awaited_once_with("stale")
+    loaded = await _load(session_factory)
+    assert loaded["stale"].swept is True
+    assert loaded["stale"].collected is False
+    assert loaded["stale"].sweep_started_at is None
+    assert loaded["active"].swept is False
+    assert loaded["active"].sweep_started_at == 950
diff --git a/tests/unit/test_settings.py b/tests/unit/test_settings.py
index a553b6d4..b51ec172 100644
--- a/tests/unit/test_settings.py
+++ b/tests/unit/test_settings.py
@@ -62,6 +62,101 @@ def test_payout_settings_have_sensible_defaults() -> None:
     assert s.payout_interval_seconds == 900
 
 
+def test_database_pool_defaults_are_bounded_and_fail_fast() -> None:
+    s = Settings()
+    assert s.database_pool_size == 5
+    assert s.database_max_overflow == 0
+    assert s.database_pool_timeout == 5.0
+    assert s.database_pool_recycle == 1800
+    assert s.database_pool_pre_ping is True
+    assert s.database_pool_hold_warn_seconds == 10.0
+
+
+@pytest.mark.parametrize(
+    ("field", "bad_value"),
+    [
+        ("database_pool_size", 0),
+        ("database_max_overflow", -1),
+        ("database_pool_timeout", 0),
+        ("database_pool_recycle", -1),
+        ("database_pool_hold_warn_seconds", 0),
+    ],
+)
+def test_database_pool_settings_reject_invalid_values(
+    field: str, bad_value: int
+) -> None:
+    with pytest.raises(ValidationError):
+        Settings(**{field: bad_value})
+
+
+@pytest.mark.asyncio
+async def test_database_pool_fields_are_env_only_not_persisted(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """DB pool sizing is infrastructure the node needs *before* it can read the
+    DB, so it can never be configured from the DB — it must never be written to
+    the settings blob, and a stale/injected DB value must never shadow env.
+    """
+    monkeypatch.setenv("DATABASE_POOL_SIZE", "7")
+
+    engine = create_async_engine("sqlite+aiosqlite:///:memory:")
+    async with AsyncSession(engine, expire_on_commit=False) as session:
+        s = await SettingsService.initialize(session)
+
+        # The env value is live for runtime consumers...
+        assert s.database_pool_size == 7
+        # ...but pool sizing is never written to the settings blob.
+        blob = await _read_settings_blob(session)
+        for field in (
+            "database_pool_size",
+            "database_max_overflow",
+            "database_pool_timeout",
+            "database_pool_recycle",
+            "database_pool_pre_ping",
+            "database_pool_hold_warn_seconds",
+        ):
+            assert field not in blob
+
+        # Even a stale blob that somehow carries a pool value must not win: env
+        # stays authoritative on the next initialize.
+        await session.exec(  # type: ignore
+            text("UPDATE settings SET data = :d WHERE id = 1").bindparams(
+                d=json.dumps({"database_pool_size": 99})
+            )
+        )
+        await session.commit()
+        again = await SettingsService.initialize(session)
+        assert again.database_pool_size == 7
+
+
+@pytest.mark.asyncio
+async def test_update_does_not_apply_env_only_fields_to_live_settings(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """DB pool sizing is env-only: a settings update must neither persist it nor
+    mutate the live value. The engine pool is already built at boot from env, so
+    a UI/API update carrying a pool value must not make the live setting diverge
+    from the running pool.
+    """
+    monkeypatch.delenv("DATABASE_POOL_SIZE", raising=False)
+    monkeypatch.setattr(settings, "database_pool_size", 5)
+
+    engine = create_async_engine("sqlite+aiosqlite:///:memory:")
+    async with AsyncSession(engine, expire_on_commit=False) as session:
+        await SettingsService.initialize(session)
+        await SettingsService.update(
+            {"database_pool_size": 99, "name": "PoolTweaker"}, session
+        )
+
+        # A non-env-only field still updates normally...
+        assert settings.name == "PoolTweaker"
+        # ...but the env-only pool size stays at the boot value.
+        assert settings.database_pool_size == 5
+        # ...and it is never written to the settings blob.
+        blob = await _read_settings_blob(session)
+        assert "database_pool_size" not in blob
+
+
 @pytest.mark.parametrize(
     "field,bad_value",
     [