Revalidate the draft pool on save, refuse duplicate swaps, refresh the Quest log after a draft

Feature 14 integration fix (Maestro 857e4c33-e250-46ec-b5ea-7dd4f3b719d9).

- F14-01: storeDraft re-reads the draft pool (ListDraftPool, the same
  eligibility rule draft_week was given) inside the save transaction. A
  day whose dinner was archived, moved to tried, or planned on another
  current or later week while draft_week ran fails the job with the new
  retryable reason pool_changed and stores nothing.
- F14-02: Swap refuses a dinner already on another day of the week inside
  the write transaction; the API answers 409 dinner_already_planned.
- F14-03: a finished draft invalidates the Quest log query, as the swap
  path does, so the tablet strip and desktop panel drop dinners it planned.

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

internal/server/plans.go

@@ -107,8 +107,8 @@ func weekStartOrFail(w http.ResponseWriter, r *http.Request, logger *slog.Logger
 // writePlanError maps a plan.Service error to its API error: a week with
 // no plan or an unknown dinner is 404, a date outside the week is 400, and
 // drafting over a synced plan without confirm, a confirmed draft while an
-// unconfirmed one runs, or planning a dinner that is neither a Regular nor
-// in the Quest log, is 409.
+// unconfirmed one runs, planning a dinner that is neither a Regular nor in
+// the Quest log, or one already on another day of the week, is 409.
 func writePlanError(w http.ResponseWriter, r *http.Request, logger *slog.Logger, action string, err error) {
 	var day *plan.InvalidDayError
 	var week *plan.InvalidWeekError
@@ -120,6 +120,8 @@ func writePlanError(w http.ResponseWriter, r *http.Request, logger *slog.Logger,
 		writeError(w, r, logger, http.StatusBadRequest, "invalid_week", week.Error())
 	case errors.As(err, &notPlannable):
 		writeError(w, r, logger, http.StatusConflict, "dinner_not_plannable", notPlannable.Error())
+	case errors.Is(err, plan.ErrDinnerAlreadyPlanned):
+		writeError(w, r, logger, http.StatusConflict, "dinner_already_planned", err.Error())
 	case errors.Is(err, plan.ErrConfirmRequired):
 		writeError(w, r, logger, http.StatusConflict, "confirm_required", err.Error())
 	case errors.Is(err, plan.ErrDraftRunning):

internal/server/plans_test.go

@@ -309,6 +309,7 @@ func TestPutPlanDay(t *testing.T) {
 		{"2026-10-12/days/2026-10-32", `{"dinner_id":"` + e.questLog + `"}`, http.StatusBadRequest, "invalid_date"},
 		{"2026-10-12/days/2026-10-14", `{"dinner_id":"no-such-dinner"}`, http.StatusNotFound, "not_found"},
 		{"2026-10-19/days/2026-10-20", `{"dinner_id":"` + e.questLog + `"}`, http.StatusNotFound, "not_found"},
+		{"2026-10-12/days/2026-10-15", `{"dinner_id":"` + e.questLog + `"}`, http.StatusConflict, "dinner_already_planned"},
 	} {
 		rec, body := callDinners(t, e.h, http.MethodPut, plansPath+tc.target, tc.body)
 		if rec.Code != tc.status || errorCode(body) != tc.code {