fix(quota-share): keep #5923 silent-stop bookkeeping on the no-targets early exit

The #11371 slot-release replaced (instead of augmenting) the recordComboFailure
call on the no-executable-targets path, freezing the pin auto-clear counter.
Restore both effects side by side + regression guard in combo-routing-engine.

Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>

open-sse/services/combo.ts

@@ -955,6 +955,7 @@ async function handleComboChatInner({
     // Surface a recovery hint + auto-clear the session pin after enough consecutive
     // no-target failures (silent-stop fix). Threshold of 3 prevents a one-off account
     // wipe from destroying the prompt-cache pin benefit on the next request.
+    recordComboFailure(effectiveSessionId, combo.name);
     // #11371: same early-exit release as the pinned-turn path above.
     targetResolution.quotaShareRelease?.();
     return errorResponseWithComboDiagnostics(

tests/unit/combo-routing-engine.test.ts

@@ -16,6 +16,9 @@ const {
   handleComboChat,
 } = await import("../../open-sse/services/combo.ts");
 const { resolveComboTargets } = await import("../../open-sse/services/combo/comboStructure.ts");
+const { getComboFailureCount, __resetComboFailureTrackerForTests } = await import(
+  "../../open-sse/services/combo/failureTracker.ts"
+);
 const { applyPromptCacheAffinity } =
   await import("../../open-sse/services/combo/promptCacheAffinity.ts");
 const { resolveReasoningBufferedMaxTokens } =
@@ -1327,6 +1330,43 @@ test("handleComboChat returns 404 model_not_found when a combo has no executable
   assert.match(payload.error.message, /Combo has no executable targets/);
 });
 
+test("#11408 guard: no-executable-targets early exit still records the combo failure (silent-stop counter, #5923)", async () => {
+  __resetComboFailureTrackerForTests();
+  const result = await handleComboChat({
+    body: {},
+    combo: {
+      name: "guard-empty-11408",
+      strategy: "priority",
+      models: [],
+      context_cache_protection: true,
+    },
+    handleSingleModel: async () => {
+      throw new Error("handleSingleModel should not run for empty combos");
+    },
+    isModelAvailable: async () => true,
+    log: createLog(),
+    settings: {
+      comboDefaults: {
+        maxRetries: 0,
+        retryDelayMs: 1,
+      },
+    },
+    relayOptions: { sessionId: "sess-guard-11408" } as any,
+    allCombos: null,
+  });
+
+  const payload = (await result.json()) as any;
+  assert.equal(result.status, 404);
+  // The quota-share slot release must not replace the #5923 silent-stop
+  // bookkeeping: the consecutive-failure counter must still advance so the
+  // session pin auto-clears after COMBO_FAILURE_THRESHOLD no-target failures.
+  assert.equal(
+    getComboFailureCount("sess-guard-11408", "guard-empty-11408"),
+    1,
+    "recordComboFailure must run on the no-executable-targets early exit"
+  );
+});
+
 test("handleComboChat round-robin returns 404 when no models are configured", async () => {
   const result = await handleComboChat({
     body: {},