prevent zero balance token

routstr/auth.py

@@ -341,6 +341,11 @@ async def validate_bearer_key(
                     "Token redemption returned zero or negative amount",
                     extra={"msats": msats, "key_hash": hashed_key[:8] + "..."},
                 )
+                # Defense-in-depth: credit_balance now refuses to commit on a
+                # zero/negative redemption, but if a row was nonetheless
+                # persisted, drop it so we never leave an orphan zero-balance key.
+                await session.delete(new_key)
+                await session.commit()
                 raise Exception("Token redemption failed")
 
             await session.refresh(new_key)

routstr/wallet.py

@@ -403,6 +403,20 @@ async def credit_balance(
                 "credit_balance: Converted to msat", extra={"amount_msat": amount}
             )
 
+        # Guard against zero/negative redemptions (empty or dust tokens, or
+        # swap-to-primary-mint amounts that net to <= 0 after fees). Raising here
+        # — before the UPDATE/commit below — leaves any freshly-created, still
+        # uncommitted ApiKey row to be rolled back when the request session
+        # closes, instead of persisting an orphan key with balance 0.
+        if amount <= 0:
+            logger.error(
+                "credit_balance: Redeemed amount is zero or negative; refusing to credit",
+                extra={"amount": amount, "unit": unit, "mint_url": mint_url},
+            )
+            raise ValueError(
+                f"Redeemed token amount must be positive, got {amount} msats"
+            )
+
         logger.info(
             "credit_balance: Updating balance",
             extra={"old_balance": key.balance, "credit_amount": amount},

tests/unit/test_wallet.py

@@ -108,6 +108,39 @@ async def test_credit_balance() -> None:
             assert mock_session.refresh.called
 
 
+@pytest.mark.asyncio
+async def test_credit_balance_rejects_zero_amount() -> None:
+    """A zero/dust redemption must raise BEFORE any commit, so no orphan
+    zero-balance key (balance 0, total_spent 0, total_requests 0) is persisted."""
+    token_data = {
+        "token": [{"mint": "http://mint:3338", "proofs": [{"amount": 0}]}],
+        "unit": "sat",
+    }
+    token_json = json.dumps(token_data)
+    token_b64 = base64.urlsafe_b64encode(token_json.encode()).decode()
+    token_str = f"cashuA{token_b64}"
+
+    mock_key = Mock()
+    mock_key.balance = 0
+    mock_key.hashed_key = "test_hash"
+    mock_session = AsyncMock()
+
+    from routstr.core.settings import settings
+
+    with patch.object(settings, "cashu_mints", ["http://mint:3338"]):
+        with patch(
+            "routstr.wallet.recieve_token",
+            return_value=(0, "sat", "http://mint:3338"),
+        ):
+            with pytest.raises(ValueError, match="must be positive"):
+                await credit_balance(token_str, mock_key, mock_session)
+
+    # Critically: no balance UPDATE and no commit happened, so the caller's
+    # uncommitted key row rolls back instead of persisting as an orphan.
+    assert not mock_session.exec.called
+    assert not mock_session.commit.called
+
+
 @pytest.mark.asyncio
 async def test_swap_to_primary_mint_insufficient_for_fees() -> None:
     """Token amount is less than melt_quote.amount + melt_quote.fee_reserve."""