Push the week's plan to Google Calendar (Feature 16)

POST /api/v1/plans/{weekStart}/push-calendar writes one event per plan
day to the chosen calendar: "Dinner: {name}" from the household dinner
time for 60 minutes in the household zone, with the dinner name,
"Start by {time}" for crock-pot dinners and the
{MEALQUEST_PUBLIC_URL}/dinner/{id} link. Event ids are the lowercase
base32hex SHA-256 of "mealquest|{weekStart}|{date}"; each event is
inserted, and a 409 updates it instead.

gcal.Service.PushEvents does the Calendar writes under the account lock,
with the same redaction as listing. plan.Service.Push records a push only
when every event was written: the plan becomes synced with
calendar_synced_at and each day stores its event id. A partial failure
records nothing; a plan edited mid-push is 409 plan_changed.

A swap, or a redraft to another dinner, clears the day's
calendar_event_id, so the next push writes just those days; a push with
none pending writes every day again.

No calendar chosen is 409 no_calendar; a deleted or read-only chosen
calendar is 409 calendar_unavailable; a refused grant is 502
reconnect_required, leaving the connection as it is.

Maestro task 5885d2b1-cf06-44ff-abf3-242d7763c3c9.

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

internal/server/plans.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/go-chi/chi/v5"
 
+	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/gcal"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/plan"
 	"code.cubecraftlabs.com/Maniacs_Mansion/Meal-Quest/internal/store"
 )
@@ -93,6 +94,58 @@ func putPlanDay(logger *slog.Logger, svc *plan.Service) http.HandlerFunc {
 	}
 }
 
+// postPlanPush pushes the week's plan to the chosen Google calendar
+// (Push to Calendar) and answers with the plan as synced.
+func postPlanPush(logger *slog.Logger, svc *plan.Service) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		week, ok := weekStartOrFail(w, r, logger)
+		if !ok {
+			return
+		}
+		p, err := svc.Push(r.Context(), week)
+		if err != nil {
+			writePlanPushError(w, r, logger, err)
+			return
+		}
+		writeJSON(w, r, logger, http.StatusOK, p)
+	}
+}
+
+// writePlanPushError maps a Push to Calendar error to its API error: 409
+// not_connected when Google Calendar is not connected, no_calendar when no
+// calendar is chosen, calendar_unavailable when the chosen calendar was
+// deleted or is no longer writable, and plan_changed when the plan was
+// edited during the push; 502 reconnect_required when Google no longer
+// accepts the grant, and google_failed when Google refused or could not be
+// reached. A failed push leaves the plan's status as it was. Any other
+// error is the plan's, as writePlanError maps it.
+func writePlanPushError(w http.ResponseWriter, r *http.Request, logger *slog.Logger, err error) {
+	var calendar *gcal.CalendarError
+	switch {
+	case errors.Is(err, gcal.ErrNotConnected):
+		writeError(w, r, logger, http.StatusConflict, "not_connected", "Google Calendar is not connected")
+	case errors.Is(err, gcal.ErrNoCalendar):
+		writeError(w, r, logger, http.StatusConflict, "no_calendar",
+			"choose the calendar to push dinners to in Settings, then push again")
+	case errors.Is(err, gcal.ErrCalendarUnavailable):
+		logger.WarnContext(r.Context(), "push plan to Calendar", "error", err)
+		writeError(w, r, logger, http.StatusConflict, "calendar_unavailable",
+			"the chosen calendar was deleted or MealQuest can no longer add dinners to it; choose another calendar in Settings")
+	case errors.Is(err, plan.ErrPlanChanged):
+		writeError(w, r, logger, http.StatusConflict, "plan_changed", err.Error())
+	case errors.Is(err, gcal.ErrReconnect):
+		logger.WarnContext(r.Context(), "push plan to Calendar", "error", err)
+		writeError(w, r, logger, http.StatusBadGateway, "reconnect_required",
+			"Google no longer accepts MealQuest's access to your calendar; connect Google Calendar again")
+	case errors.As(err, &calendar):
+		logger.WarnContext(r.Context(), "push plan to Calendar", "error", err)
+		writeError(w, r, logger, http.StatusBadGateway, "google_failed",
+			"Google Calendar could not be reached; push again")
+	default:
+		writePlanError(w, r, logger, "push plan to Calendar", err)
+	}
+}
+
 // weekStartOrFail parses the {weekStart} path parameter, or answers 400
 // when it is not a Monday date.
 func weekStartOrFail(w http.ResponseWriter, r *http.Request, logger *slog.Logger) (store.LocalDate, bool) {