M8-R03B: keep meter swap recompute in caller transaction

app/api/routes/api/meters.py

@@ -151,7 +151,7 @@ def _trigger_recompute(db: Session, start: datetime, label: str) -> int:
         # started_at is in the future — nothing to recompute.
         logger.info("%s: started_at (%s) is in the future, skipping recompute.", label, start)
         return 0
-    n = recompute_range(db, start, end)
+    n = recompute_range(db, start, end, commit=False)
     logger.info(
         "%s: recomputed %d period(s) in window [%s, %s).",
         label,
@@ -352,11 +352,6 @@ def patch_energy_meter(
             note=body.note,
             started_at=new_started_at_utc,
         )
-    except MeterIntervalError as exc:
-        raise HTTPException(
-            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
-            detail=str(exc),
-        )
 
         # Retroactive recompute if started_at was changed.
         if new_started_at_utc is not None and old_started_at is not None:
@@ -369,6 +364,15 @@ def patch_energy_meter(
             _trigger_recompute(db, window_start, f"PATCH /api/energy/meters/{meter_id}")
 
         db.commit()
+    except MeterIntervalError as exc:
+        db.rollback()
+        raise HTTPException(
+            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
+            detail=str(exc),
+        )
+    except Exception:
+        db.rollback()
+        raise
     db.refresh(meter)
 
     # Trigger HA discovery re-publish so label renames on the active meter

app/services/energy_cost.py

@@ -665,7 +665,9 @@ def compute_closed_periods(session: Session) -> int:
 # ---------------------------------------------------------------------------
 
 
-def recompute_range(session: Session, start: datetime, end: datetime) -> int:
+def recompute_range(
+    session: Session, start: datetime, end: datetime, *, commit: bool = True
+) -> int:
     """Recompute (overwrite) all 15-minute periods in ``[start, end)``.
 
     This is the *explicit opt-in* path for recovering from:
@@ -686,8 +688,11 @@ def recompute_range(session: Session, start: datetime, end: datetime) -> int:
     Parameters
     ----------
     session:
-        Active SQLAlchemy session.  The function commits after all periods
+        Active SQLAlchemy session.
-        have been processed.
+    commit:
+        When true (the default), commit after all periods have been processed.
+        Callers composing this recompute with other writes may pass false and
+        own the surrounding transaction themselves.
     start:
         Inclusive start datetime (floored to the nearest quarter-hour internally).
     end:
@@ -724,6 +729,7 @@ def recompute_range(session: Session, start: datetime, end: datetime) -> int:
                 )
         t0 += timedelta(minutes=_PERIOD_MINUTES)
 
+    if commit:
         session.commit()
     logger.info(
         "recompute_range(%s, %s): wrote %d period(s).",

tests/test_api_meters.py

@@ -36,10 +36,10 @@ from unittest.mock import patch
 
 import pytest
 from fastapi.testclient import TestClient
-from sqlalchemy import create_engine, select
+from sqlalchemy import create_engine, event, select
 from sqlalchemy.orm import Session
 
-from app.models.energy import Meter
+from app.models.energy import EnergyCostPeriod, Meter
 from app.models.meter_source import MeterSource, MeterSourceBinding, MeterSourceChannel
 
 # ---------------------------------------------------------------------------
@@ -443,6 +443,54 @@ def test_declare_meter_recompute_failure_rolls_back_handoff(meters_client):
         assert session.execute(select(MeterSourceBinding)).scalar_one().ended_at is None
 
 
+def test_declare_meter_final_commit_failure_rolls_back_handoff_and_recompute(meters_client):
+    """A real recompute remains uncommitted until the route's final commit succeeds."""
+    client, engine = meters_client
+    _login(client)
+    boundary = datetime.now(UTC) - timedelta(minutes=45)
+    boundary = boundary.replace(minute=boundary.minute - boundary.minute % 15, second=0, microsecond=0)
+    old_start = boundary - timedelta(days=1)
+
+    with Session(engine) as session:
+        old_meter = Meter(
+            label="Old meter",
+            commodity="electricity",
+            started_at=old_start,
+            reason="initial",
+            created_at=old_start,
+        )
+        session.add(old_meter)
+        session.commit()
+        old_id = old_meter.id
+    channel_uuid = _add_bound_channel(engine, meter_id=old_id, started_at=old_start)
+
+    def fail_final_commit(_session: Session) -> None:
+        raise RuntimeError("final commit failed")
+
+    event.listen(Session, "before_commit", fail_final_commit)
+    try:
+        with pytest.raises(RuntimeError, match="final commit failed"):
+            client.post(
+                "/api/energy/meters",
+                json=_declare_payload(
+                    label="New meter",
+                    started_at=boundary.isoformat(),
+                    reason="meter_swap",
+                    source_channel_uuid=channel_uuid,
+                ),
+                headers={"X-CSRF-Token": _CSRF},
+            )
+    finally:
+        event.remove(Session, "before_commit", fail_final_commit)
+
+    with Session(engine) as session:
+        assert session.execute(select(Meter).where(Meter.label == "New meter")).scalar_one_or_none() is None
+        assert session.get(Meter, old_id).ended_at is None
+        binding = session.execute(select(MeterSourceBinding)).scalar_one()
+        assert binding.ended_at is None
+        assert session.execute(select(EnergyCostPeriod)).scalars().all() == []
+
+
 def test_declare_meter_overlap_returns_422(meters_client):
     """Declaring a meter with started_at before active meter's started_at → 422."""
     client, _ = meters_client
@@ -546,6 +594,7 @@ def test_declare_meter_retroactive_triggers_recompute(meters_client):
         assert resp.status_code == 201
         # recompute_range should have been called with start == t_past
         assert mock_recompute.called
+        assert mock_recompute.call_args.kwargs["commit"] is False
         call_args = mock_recompute.call_args
         recompute_start = call_args[0][1]  # positional arg index 1 (session is 0)
         # Normalise for comparison
@@ -685,6 +734,7 @@ def test_patch_meter_started_at_retroactive_triggers_recompute(meters_client):
         assert resp.status_code == 200
         # recompute should be triggered
         assert mock_recompute.called
+        assert mock_recompute.call_args.kwargs["commit"] is False
         call_args = mock_recompute.call_args
         recompute_start = call_args[0][1]
         if recompute_start.tzinfo is None:

tests/test_energy_cost.py

@@ -2176,6 +2176,32 @@ class TestComputeClosedPeriods:
 
 
 class TestRecomputeRange:
+    def test_default_commit_is_visible_to_a_new_session(self, energy_db: Session) -> None:
+        """The public recompute API retains its standalone commit behaviour."""
+        _setup_manual_scenario(energy_db)
+
+        assert recompute_range(energy_db, _T0, _T1) == 1
+        assert energy_db.bind is not None
+        with Session(energy_db.bind) as observer:
+            row = observer.execute(
+                select(EnergyCostPeriod).where(EnergyCostPeriod.period_start == _T0)
+            ).scalar_one()
+            assert row.degraded is False
+
+    def test_commit_false_leaves_recompute_for_caller_to_rollback(self, energy_db: Session) -> None:
+        """Caller-owned recompute writes disappear entirely after rollback."""
+        _setup_manual_scenario(energy_db)
+
+        assert recompute_range(energy_db, _T0, _T1, commit=False) == 1
+        energy_db.rollback()
+
+        assert energy_db.bind is not None
+        with Session(energy_db.bind) as observer:
+            rows = observer.execute(
+                select(EnergyCostPeriod).where(EnergyCostPeriod.period_start == _T0)
+            ).scalars().all()
+            assert rows == []
+
     def test_overwrites_existing_rows(self, energy_db: Session) -> None:
         """recompute_range must overwrite non-degraded rows (explicit opt-in)."""
         contract = _make_contract(energy_db, kind="manual", active=True)