feat(store): add DeleteUser with cascading account deletion

backend/internal/store/users_test.go

@@ -89,3 +89,76 @@ func TestProvisionUser_TwoUsersGetIndependentTaxonomies(t *testing.T) {
 		t.Fatal("expected each user's seeded kinds to be distinct rows")
 	}
 }
+
+func TestDeleteUser_RemovesUserAndCascadesEverything(t *testing.T) {
+	db := openTestDB(t)
+	ctx := context.Background()
+
+	userID, err := db.ProvisionUser(ctx, "delete-me", "Delete Me")
+	if err != nil {
+		t.Fatalf("ProvisionUser: %v", err)
+	}
+
+	activityID, err := db.UpsertActivity(ctx, userID, Activity{GarminActivityID: 1, StartTimeUTC: "2026-07-11 06:00:00", RawJSON: "{}"})
+	if err != nil {
+		t.Fatalf("UpsertActivity: %v", err)
+	}
+	kindID, err := db.CreateWorkoutKind(ctx, userID, WorkoutKind{Name: "Test Delete Kind", RuleJSON: `{"match":"all","conditions":[]}`, IsActive: true})
+	if err != nil {
+		t.Fatalf("CreateWorkoutKind: %v", err)
+	}
+	if err := db.ReplaceLaps(ctx, userID, activityID, []Lap{{LapIndex: 1}}); err != nil {
+		t.Fatalf("ReplaceLaps: %v", err)
+	}
+	if err := db.ReplaceActivitySamples(ctx, userID, activityID, []Sample{{ElapsedSeconds: 0}}); err != nil {
+		t.Fatalf("ReplaceActivitySamples: %v", err)
+	}
+	if _, err := db.InsertKindAssignment(ctx, userID, KindAssignment{
+		ActivityID: activityID, WorkoutKindID: &kindID, AssignmentSource: AssignmentSourceRuleEngine,
+		Status: AssignmentStatusAssigned, CandidateKindsJSON: "[]",
+	}); err != nil {
+		t.Fatalf("InsertKindAssignment: %v", err)
+	}
+	minPace := 300.0
+	if err := db.UpdateWorkoutTypePace(ctx, userID, WorkoutTypePace{WorkoutKindID: kindID, PaceMinSecPerKm: &minPace}); err != nil {
+		t.Fatalf("UpdateWorkoutTypePace: %v", err)
+	}
+	if err := db.UpdateSyncState(ctx, userID, "2020-01-01", true); err != nil {
+		t.Fatalf("UpdateSyncState: %v", err)
+	}
+	if _, err := db.StartSyncRun(ctx, userID, SyncKindBackfill); err != nil {
+		t.Fatalf("StartSyncRun: %v", err)
+	}
+
+	if err := db.DeleteUser(ctx, userID); err != nil {
+		t.Fatalf("DeleteUser: %v", err)
+	}
+
+	if _, found, err := db.GetUserBySub(ctx, "delete-me"); err != nil || found {
+		t.Fatalf("expected user gone after DeleteUser, found=%v err=%v", found, err)
+	}
+
+	checks := []struct {
+		query string
+		arg   int64
+	}{
+		{`SELECT COUNT(*) FROM profile WHERE user_id = ?`, userID},
+		{`SELECT COUNT(*) FROM workout_kinds WHERE user_id = ?`, userID},
+		{`SELECT COUNT(*) FROM workout_type_paces WHERE workout_kind_id = ?`, kindID},
+		{`SELECT COUNT(*) FROM activities WHERE user_id = ?`, userID},
+		{`SELECT COUNT(*) FROM laps WHERE activity_id = ?`, activityID},
+		{`SELECT COUNT(*) FROM activity_samples WHERE activity_id = ?`, activityID},
+		{`SELECT COUNT(*) FROM kind_assignments WHERE activity_id = ?`, activityID},
+		{`SELECT COUNT(*) FROM sync_state WHERE user_id = ?`, userID},
+		{`SELECT COUNT(*) FROM sync_runs WHERE user_id = ?`, userID},
+	}
+	for _, c := range checks {
+		var count int
+		if err := db.QueryRowContext(ctx, c.query, c.arg).Scan(&count); err != nil {
+			t.Fatalf("count query %q: %v", c.query, err)
+		}
+		if count != 0 {
+			t.Errorf("query %q: got %d rows, want 0 after DeleteUser", c.query, count)
+		}
+	}
+}