store: scope kind assignments, laps, and samples via activity ownership

None of these three tables gained their own user_id column -- they're
always accessed through a specific activity, so ownership is checked via a
join/subquery against activities.user_id instead.

backend/internal/store/store_test.go

@@ -143,7 +143,7 @@ func TestKindAssignment_AppendOnlyHistoryAndCurrentView(t *testing.T) {
 	}
 
 	// First: rule engine says needs_review (ambiguous).
-	if _, err := db.InsertKindAssignment(ctx, KindAssignment{
+	if _, err := db.InsertKindAssignment(ctx, userID, KindAssignment{
 		ActivityID:         activityID,
 		AssignmentSource:   AssignmentSourceRuleEngine,
 		Status:             AssignmentStatusNeedsReview,
@@ -152,7 +152,7 @@ func TestKindAssignment_AppendOnlyHistoryAndCurrentView(t *testing.T) {
 		t.Fatalf("InsertKindAssignment (rule engine): %v", err)
 	}
 
-	queue, err := db.ReviewQueue(ctx)
+	queue, err := db.ReviewQueue(ctx, userID)
 	if err != nil {
 		t.Fatalf("ReviewQueue: %v", err)
 	}
@@ -161,7 +161,7 @@ func TestKindAssignment_AppendOnlyHistoryAndCurrentView(t *testing.T) {
 	}
 
 	// Then: user manually resolves it.
-	if _, err := db.InsertKindAssignment(ctx, KindAssignment{
+	if _, err := db.InsertKindAssignment(ctx, userID, KindAssignment{
 		ActivityID:       activityID,
 		WorkoutKindID:    &kindID,
 		AssignmentSource: AssignmentSourceManual,
@@ -170,7 +170,7 @@ func TestKindAssignment_AppendOnlyHistoryAndCurrentView(t *testing.T) {
 		t.Fatalf("InsertKindAssignment (manual): %v", err)
 	}
 
-	queue, err = db.ReviewQueue(ctx)
+	queue, err = db.ReviewQueue(ctx, userID)
 	if err != nil {
 		t.Fatalf("ReviewQueue after resolve: %v", err)
 	}
@@ -178,7 +178,7 @@ func TestKindAssignment_AppendOnlyHistoryAndCurrentView(t *testing.T) {
 		t.Fatalf("expected 0 items in review queue after manual resolve, got %d", len(queue))
 	}
 
-	current, ok, err := db.CurrentAssignment(ctx, activityID)
+	current, ok, err := db.CurrentAssignment(ctx, userID, activityID)
 	if err != nil || !ok {
 		t.Fatalf("CurrentAssignment: ok=%v err=%v", ok, err)
 	}
@@ -195,7 +195,7 @@ func TestKindAssignment_AppendOnlyHistoryAndCurrentView(t *testing.T) {
 		t.Errorf("expected 2 historical assignment rows (rule engine + manual), got %d", historyCount)
 	}
 
-	forKind, err := db.AssignmentsForKind(ctx, kindID)
+	forKind, err := db.AssignmentsForKind(ctx, userID, kindID)
 	if err != nil {
 		t.Fatalf("AssignmentsForKind: %v", err)
 	}
@@ -225,15 +225,15 @@ func TestReplaceLapsIsIdempotent(t *testing.T) {
 		{LapIndex: 1, RawJSON: "{}"},
 		{LapIndex: 2, RawJSON: "{}"},
 	}
-	if err := db.ReplaceLaps(ctx, activityID, laps); err != nil {
+	if err := db.ReplaceLaps(ctx, userID, activityID, laps); err != nil {
 		t.Fatalf("ReplaceLaps (first): %v", err)
 	}
 	// Re-sync with a different set (e.g. corrected data) should fully replace, not append.
-	if err := db.ReplaceLaps(ctx, activityID, laps[:1]); err != nil {
+	if err := db.ReplaceLaps(ctx, userID, activityID, laps[:1]); err != nil {
 		t.Fatalf("ReplaceLaps (second): %v", err)
 	}
 
-	got, err := db.LapsForActivity(ctx, activityID)
+	got, err := db.LapsForActivity(ctx, userID, activityID)
 	if err != nil {
 		t.Fatalf("LapsForActivity: %v", err)
 	}
@@ -309,7 +309,7 @@ func TestForeignKeyEnforcementPostMigration(t *testing.T) {
 	}
 
 	// Inserting a kind_assignment with a valid FK reference should succeed.
-	assignmentID, err := db.InsertKindAssignment(ctx, KindAssignment{
+	assignmentID, err := db.InsertKindAssignment(ctx, userID, KindAssignment{
 		ActivityID:       activityID,
 		WorkoutKindID:    &seedKindID,
 		AssignmentSource: AssignmentSourceManual,
@@ -325,7 +325,7 @@ func TestForeignKeyEnforcementPostMigration(t *testing.T) {
 	// Inserting a kind_assignment with a nonexistent workout_kind_id should
 	// be rejected by the FK constraint, proving FK enforcement is ON.
 	nonexistentKindID := int64(999999)
-	_, err = db.InsertKindAssignment(ctx, KindAssignment{
+	_, err = db.InsertKindAssignment(ctx, userID, KindAssignment{
 		ActivityID:       activityID,
 		WorkoutKindID:    &nonexistentKindID,
 		AssignmentSource: AssignmentSourceManual,
@@ -568,6 +568,38 @@ func TestRebuildMigrationsPreserveForeignKeyReferences(t *testing.T) {
 	}
 }
 
+func TestCurrentAssignment_ScopedToOwningUser(t *testing.T) {
+	db := openTestDB(t)
+	ctx := context.Background()
+	userA, err := db.ProvisionUser(ctx, "sub-a", "A")
+	if err != nil {
+		t.Fatalf("ProvisionUser(a): %v", err)
+	}
+	userB, err := db.ProvisionUser(ctx, "sub-b", "B")
+	if err != nil {
+		t.Fatalf("ProvisionUser(b): %v", err)
+	}
+
+	activityID, err := db.UpsertActivity(ctx, userA, Activity{GarminActivityID: 1, StartTimeUTC: "2026-07-11 05:00:00", RawJSON: "{}"})
+	if err != nil {
+		t.Fatalf("UpsertActivity: %v", err)
+	}
+	if _, err := db.InsertKindAssignment(ctx, userA, KindAssignment{
+		ActivityID: activityID, AssignmentSource: AssignmentSourceRuleEngine, Status: AssignmentStatusNeedsReview, CandidateKindsJSON: "[]",
+	}); err != nil {
+		t.Fatalf("InsertKindAssignment: %v", err)
+	}
+
+	if _, found, err := db.CurrentAssignment(ctx, userB, activityID); err != nil || found {
+		t.Fatalf("expected userB to not see userA's activity assignment, found=%v err=%v", found, err)
+	}
+	if _, err := db.InsertKindAssignment(ctx, userB, KindAssignment{
+		ActivityID: activityID, AssignmentSource: AssignmentSourceManual, Status: AssignmentStatusAssigned, CandidateKindsJSON: "[]",
+	}); err == nil {
+		t.Fatal("expected InsertKindAssignment to reject an activity that doesn't belong to userB")
+	}
+}
+
 func contains(s string, substrs ...string) bool {
 	lower := strings.ToLower(s)
 	for _, substr := range substrs {