fix(runner): 保留同平台重试的并发租约

同平台 retry_same 之前会在首个 attempt 失败时释放任务级 admission 租约，下一次 attempt 继续续租旧租约并进入 upstream_submission_unknown。

现在明确区分 attempt 自有租约与任务级 admission 租约，只在 attempt 结束时释放前者；补充回归测试覆盖同平台重试继续续租 admission 租约。

验证：env -u AI_GATEWAY_TEST_DATABASE_URL go test ./... -count=1；go vet ./...；gofmt；git diff --check。

apps/api/internal/runner/service.go

@@ -1357,20 +1357,18 @@ func (s *Service) runCandidate(
 		clientErr := &clients.ClientError{Code: "rate_limit", Message: err.Error(), Retryable: retryable}
 		return clients.Response{}, &localRateLimitError{clientErr: clientErr, cause: err, retryAfter: localRateLimitRetryAfter(err)}
 	}
+	attemptOwnedLeases := append([]store.ConcurrencyLease(nil), limitResult.Leases...)
 	if admittedPlatformModelID == candidate.PlatformModelID {
-		limitResult.Leases = append(limitResult.Leases, admittedLeases...)
+		limitResult.Leases, attemptOwnedLeases = bindAttemptConcurrencyLeases(limitResult.Leases, admittedLeases)
 	}
 	rateReservationsFinalized := false
-	retainAdmittedLeases := false
 	defer func() {
 		if !rateReservationsFinalized {
 			_ = s.store.ReleaseRateLimitReservations(context.WithoutCancel(ctx), limitResult.Reservations, "attempt_failed")
 		}
 	}()
 	defer func() {
-		if !retainAdmittedLeases {
-			_ = s.store.ReleaseConcurrencyLeases(context.WithoutCancel(ctx), limitResult.Leases)
-		}
+		_ = s.store.ReleaseConcurrencyLeases(context.WithoutCancel(ctx), attemptOwnedLeases)
 	}()
 
 	attemptID, err := s.store.CreateTaskAttempt(ctx, store.CreateTaskAttemptInput{
@@ -1798,12 +1796,20 @@ func (s *Service) runCandidate(
 	}); err != nil {
 		s.logger.Warn("record cache affinity observation failed", "error", err, "clientId", candidate.ClientID)
 	}
-	if admittedPlatformModelID == candidate.PlatformModelID {
-		retainAdmittedLeases = true
-	}
 	return response, nil
 }
 
+// bindAttemptConcurrencyLeases combines task-scoped admission leases with
+// leases acquired by the current attempt. Only the latter are returned for
+// attempt cleanup: admission owns its leases across retry_same and releases
+// them when the task changes binding or reaches a terminal state.
+func bindAttemptConcurrencyLeases(attemptLeases []store.ConcurrencyLease, admissionLeases []store.ConcurrencyLease) ([]store.ConcurrencyLease, []store.ConcurrencyLease) {
+	attemptOwned := append([]store.ConcurrencyLease(nil), attemptLeases...)
+	active := append([]store.ConcurrencyLease(nil), attemptLeases...)
+	active = append(active, admissionLeases...)
+	return active, attemptOwned
+}
+
 func (s *Service) observeProviderQuotaWait(metric string) {
 	observer, ok := s.billingMetrics.(interface {
 		ObserveProviderQuotaWait(string)