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,
@@ -352,23 +352,27 @@ def patch_energy_meter(
             note=body.note,
             started_at=new_started_at_utc,
         )
+
+        # Retroactive recompute if started_at was changed.
+        if new_started_at_utc is not None and old_started_at is not None:
+            # Normalise old_started_at to UTC-aware for comparison.
+            if old_started_at.tzinfo is None:
+                old_started_at = old_started_at.replace(tzinfo=UTC)
+            # Window = [min(old, new), now) — covers all periods whose attribution
+            # may have changed due to the boundary shift in either direction.
+            window_start = min(old_started_at, new_started_at_utc)
+            _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),
         )
-
-    # Retroactive recompute if started_at was changed.
-    if new_started_at_utc is not None and old_started_at is not None:
-        # Normalise old_started_at to UTC-aware for comparison.
-        if old_started_at.tzinfo is None:
-            old_started_at = old_started_at.replace(tzinfo=UTC)
-        # Window = [min(old, new), now) — covers all periods whose attribution
-        # may have changed due to the boundary shift in either direction.
-        window_start = min(old_started_at, new_started_at_utc)
-        _trigger_recompute(db, window_start, f"PATCH /api/energy/meters/{meter_id}")
-
-    db.commit()
+    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
-        have been processed.
+        Active SQLAlchemy session.
+    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:
@@ -724,7 +729,8 @@ def recompute_range(session: Session, start: datetime, end: datetime) -> int:
                 )
         t0 += timedelta(minutes=_PERIOD_MINUTES)
 
-    session.commit()
+    if commit:
+        session.commit()
     logger.info(
         "recompute_range(%s, %s): wrote %d period(s).",
         start.isoformat(),