Handle Google token failures and report Google Calendar status

When Google refuses the stored grant (invalid_grant on refresh, or HTTP
401 from the Calendar API to the access token just refreshed) on any
Calendar call - listing, choosing or pushing - the connection becomes
reconnect required under the account lock: the refresh token is cleared
and last_sync_error set to "Google access was revoked or expired —
reconnect". The call answers 409 google_reconnect_required, and later
calls answer the same without contacting Google until a reconnect or a
disconnect. The chosen calendar and stored calendar event ids are kept:
the pushed events are still on that calendar, so forgetEvents is not
run.

HTTP 429 and 5xx from the token endpoint or the Calendar API are retried
at most twice with backoff, then answered 503 google_unavailable,
retryable, without clearing or disconnecting anything.

Add GET /api/v1/integrations/google, reporting not_connected, connected
or reconnect_required with the chosen calendar and last_sync_error.

Migration 0015 rebuilds integrations_google so refresh_token_ct can be
cleared, with a CHECK that a row without a token carries the reason.

Maestro task b8d8da5a-0450-4571-963e-b3dfead24283.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/gcal/connect.go

@@ -122,6 +122,9 @@ type Service struct {
 	calendarAPI string
 	client      *http.Client
 	cookie      auth.FlowCookie
+	// retryDelay is the wait before the first retry of a transient
+	// failure; tests shorten it.
+	retryDelay time.Duration
 	// now is the clock; tests replace it.
 	now func() time.Time
 
@@ -170,6 +173,7 @@ func NewService(st *store.Store, box *secretbox.Box, cfg Config) (*Service, erro
 		calendarAPI: cfg.CalendarAPI,
 		client:      &http.Client{Timeout: googleTimeout, CheckRedirect: auth.CheckRedirect},
 		cookie:      auth.NewFlowCookie(connectCookieName, connectCookieKeyLabel, connectCookieTTL, cfg.SecretKey),
+		retryDelay:  firstRetryDelay,
 		now:         time.Now,
 		pending:     map[string]time.Time{},
 	}, nil
@@ -343,6 +347,9 @@ func (s *Service) store(ctx context.Context, sealed []byte) error {
 // MealQuest's access in their Google account) counts as revoked. Any other
 // revoke failure keeps the connection so the household can retry.
 //
+// A connection whose grant Google already refused (reconnect required, no
+// refresh token stored) has nothing to revoke and is deleted.
+//
 // No calendar is chosen once disconnected, so the same transaction that
 // deletes the connection forgets every pushed event (forgetEvents): every
 // synced plan becomes changed, and the next push after connecting again and
@@ -350,20 +357,19 @@ func (s *Service) store(ctx context.Context, sealed []byte) error {
 func (s *Service) Disconnect(ctx context.Context) error {
 	s.account.Lock()
 	defer s.account.Unlock()
-	row, err := db.New(s.st.Reader).GetIntegrationsGoogle(ctx)
-	if errors.Is(err, sql.ErrNoRows) {
-		return ErrNotConnected
-	}
+	row, err := s.connection(ctx)
 	if err != nil {
-		return fmt.Errorf("gcal: read Google integration: %w", err)
-	}
-	token, err := s.box.Decrypt(row.RefreshTokenCt)
-	if err != nil {
-		return fmt.Errorf("gcal: open refresh token: %w", err)
-	}
-	if err := s.revoke(ctx, string(token)); err != nil {
 		return err
 	}
+	if row.RefreshTokenCt != nil {
+		token, err := s.box.Decrypt(row.RefreshTokenCt)
+		if err != nil {
+			return fmt.Errorf("gcal: open refresh token: %w", err)
+		}
+		if err := s.revoke(ctx, string(token)); err != nil {
+			return err
+		}
+	}
 	return s.st.WithTx(ctx, func(tx *sql.Tx) error {
 		q := db.New(tx)
 		if err := q.DeleteIntegrationsGoogle(ctx); err != nil {