feat: add local thread reopen store API

internal/store/threads.go

@@ -160,6 +160,28 @@ func (s *Store) CloseThreadLocally(ctx context.Context, repoID int64, number int
 	return nil
 }
 
+func (s *Store) ReopenThreadLocally(ctx context.Context, repoID int64, number int) error {
+	if repoID <= 0 {
+		return fmt.Errorf("repo id must be positive")
+	}
+	if number <= 0 {
+		return fmt.Errorf("thread number must be positive")
+	}
+	updatedAt := time.Now().UTC().Format(timeLayout)
+	result, err := s.q().ExecContext(ctx, `
+		update threads
+		set closed_at_local = null, close_reason_local = null, updated_at = ?
+		where repo_id = ? and number = ?
+	`, updatedAt, repoID, number)
+	if err != nil {
+		return fmt.Errorf("reopen thread locally: %w", err)
+	}
+	if affected, err := result.RowsAffected(); err == nil && affected == 0 {
+		return fmt.Errorf("thread #%d was not found", number)
+	}
+	return nil
+}
+
 func scanThread(rows interface {
 	Scan(dest ...any) error
 }) (Thread, error) {

internal/store/threads_test.go

@@ -99,6 +99,17 @@ func TestCloseThreadLocallyHidesThreadAndSurvivesUpsert(t *testing.T) {
 	if len(openRows) != 0 {
 		t.Fatalf("upsert should preserve local close, got %#v", openRows)
 	}
+
+	if err := st.ReopenThreadLocally(ctx, repoID, 42); err != nil {
+		t.Fatalf("reopen thread locally: %v", err)
+	}
+	openRows, err = st.ListThreads(ctx, repoID, false)
+	if err != nil {
+		t.Fatalf("list reopened threads: %v", err)
+	}
+	if len(openRows) != 1 || openRows[0].ClosedAtLocal != "" || openRows[0].CloseReasonLocal != "" {
+		t.Fatalf("reopened thread not visible/cleared: %#v", openRows)
+	}
 }
 
 func TestCloseThreadLocallyRequiresExistingThread(t *testing.T) {
@@ -113,3 +124,16 @@ func TestCloseThreadLocallyRequiresExistingThread(t *testing.T) {
 		t.Fatal("expected missing thread error")
 	}
 }
+
+func TestReopenThreadLocallyRequiresExistingThread(t *testing.T) {
+	ctx := context.Background()
+	st, err := Open(ctx, filepath.Join(t.TempDir(), "gitcrawl.db"))
+	if err != nil {
+		t.Fatalf("open store: %v", err)
+	}
+	defer st.Close()
+
+	if err := st.ReopenThreadLocally(ctx, 1, 404); err == nil {
+		t.Fatal("expected missing thread error")
+	}
+}