fix(store): gate ActivitiesMissingWorkout on details already fetched

fillPendingDetails and fillPendingWorkouts are each independently
LIMIT-bounded over different candidate sets, so on a large first
backfill a structured-workout activity could fall inside the workouts
pass's window while still outside the details pass's window.
fillActivityWorkout would then align workout targets against zero laps
(details/laps never written yet) and unconditionally mark
workout_raw_json non-NULL, permanently losing that activity's target
pace/HR bands once its real laps arrived later -- silently, with no
error.

Add details_fetched_at IS NOT NULL to ActivitiesMissingWorkout's and
CountActivitiesMissingWorkout's WHERE clause: an activity is only
eligible for a workout fetch once its laps actually exist to align
against. This still covers the intended retry case (an activity whose
workout fetch previously failed always has details_fetched_at already
set) while excluding never-yet-processed activities.

Rename/rewrite the store test to assert the corrected exclusion
(count=1, not 2) as an explicit regression test, and fix the
TestSyncStatus_ReportsPhaseAwareProgressAndWorkoutsPending API fixture,
which exercised the same buggy shape.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/internal/store/activities.go

@@ -276,16 +276,24 @@ func (db *DB) CountActivitiesMissingDetails(ctx context.Context, userID int64) (
 // ActivitiesMissingWorkout returns userID's activities that have a
 // structured workout (WorkoutID set at initial upsert time, straight from
 // Garmin's activity summary) but haven't had get_workout_by_id fetched yet.
-// Independently queryable from ActivitiesMissingDetails: workout_id is
-// known well before any detail fetch, and workout_raw_json is only ever
-// set by SetActivityWorkout, so this also picks up an activity whose
-// details were fetched successfully in some prior run but whose workout
-// fetch failed back then -- ActivitiesMissingDetails would never surface
-// that activity again (details_fetched_at/splits_fetched_at are already
-// set), silently losing its target pace/HR bands forever without this.
+// Gated on details_fetched_at IS NOT NULL: fillActivityWorkout resolves each
+// lap's target pace/HR band via alignWorkoutTargets, which needs the
+// activity's laps already written by fillActivityDetails -- without this
+// gate, a structured-workout activity whose details/laps haven't been
+// fetched yet would fall into a separate, independently LIMIT-bounded batch
+// than fillPendingDetails's, get its workout_raw_json set against zero laps
+// (a silent no-op alignment), and then never be retried once its laps
+// finally arrive, since workout_raw_json IS NULL is the only signal this
+// query has left. This is still independent of splits_fetched_at (unlike
+// ActivitiesMissingDetails, which requires both): splits/laps aren't needed
+// to resolve workout targets, only details_fetched_at is. It also still
+// covers the intended retry case -- an activity whose workout fetch
+// previously failed after details succeeded always has details_fetched_at
+// already set, so it's still surfaced here -- while excluding activities
+// that simply haven't been processed by fillActivityDetails at all yet.
 func (db *DB) ActivitiesMissingWorkout(ctx context.Context, userID int64, limit int) ([]Activity, error) {
 	rows, err := db.QueryContext(ctx, `SELECT `+activityColumns+` FROM activities
-		WHERE user_id = ? AND workout_id IS NOT NULL AND workout_raw_json IS NULL
+		WHERE user_id = ? AND workout_id IS NOT NULL AND workout_raw_json IS NULL AND details_fetched_at IS NOT NULL
 		ORDER BY start_time_utc DESC LIMIT ?`, userID, limit)
 	if err != nil {
 		return nil, fmt.Errorf("list activities missing workout for user %d: %w", userID, err)
@@ -306,11 +314,12 @@ func (db *DB) ActivitiesMissingWorkout(ctx context.Context, userID int64, limit
 // CountActivitiesMissingWorkout returns how many of userID's activities
 // still need get_workout_by_id fetched, regardless of any per-call batch
 // limit -- used to report overall remaining work, mirroring
-// CountActivitiesMissingDetails.
+// CountActivitiesMissingDetails. See ActivitiesMissingWorkout for why this
+// is additionally gated on details_fetched_at IS NOT NULL.
 func (db *DB) CountActivitiesMissingWorkout(ctx context.Context, userID int64) (int, error) {
 	var n int
 	err := db.QueryRowContext(ctx, `SELECT COUNT(*) FROM activities
-		WHERE user_id = ? AND workout_id IS NOT NULL AND workout_raw_json IS NULL`, userID).Scan(&n)
+		WHERE user_id = ? AND workout_id IS NOT NULL AND workout_raw_json IS NULL AND details_fetched_at IS NOT NULL`, userID).Scan(&n)
 	if err != nil {
 		return 0, fmt.Errorf("count activities missing workout for user %d: %w", userID, err)
 	}