fix(responses-continuation): fail closed on a log-truncated stored input/output array (#11473)

Validated in a combined 2-PR batch worktree off release/v3.8.51 tip.
- Focused test: responses-continuation-store.test.ts — part of batch's 46/46 node:test run
- typecheck:core, file-size, changelog-integrity, complexity, cognitive-complexity — all OK
- Full-repo lint: 228 pre-existing dashboard react-hooks/* findings, unrelated to this diff

Thanks for the live-verified root cause — a truncation sentinel getting forwarded upstream as a real Responses-API item, breaking the turn with a genuine 400, is exactly the kind of defect that's easy to miss without production traffic to reproduce against.

tests/unit/responses-continuation-store.test.ts

@@ -223,6 +223,44 @@ test("resolvePreviousResponseState resolves input from clientRawRequest when pro
   });
 });
 
+test("resolvePreviousResponseState fails closed when the stored input array was log-truncated", () => {
+  // Real production shape: cloneBoundedChatLogPayload (chatCore/logTruncation.ts)
+  // and cloneBoundedForLog (utils/requestLogger.ts) both prepend an
+  // `_omniroute_truncated_array` sentinel in place of the items they dropped
+  // once a logged array exceeds their tail-item cap (~24 items) -- routine
+  // for any conversation that's been going a while, not an edge case. Reading
+  // that sentinel back as a real Responses-API item and forwarding it upstream
+  // produced a live 400: "input item type 'missing' cannot be represented in
+  // Chat Completions" -- worse than the plain cache-miss this function is
+  // otherwise designed to fail into.
+  insertCallLog({
+    id: "log-7",
+    responseId: "resp_gen-truncated-history",
+    apiKeyId: "key-1",
+    detailState: "ready",
+    artifactRelPath: "2026-01-01/log-7.json",
+  });
+  writeArtifact("2026-01-01/log-7.json", {
+    clientRawRequest: {
+      body: {
+        input: [
+          { _omniroute_truncated_array: true, originalLength: 26, retainedTailItems: 24 },
+          { type: "function_call_output", call_id: "call_1", output: "ok" },
+        ],
+      },
+    },
+    providerRequest: { body: { input: [] } },
+    clientResponse: {
+      summary: {
+        id: "resp_gen-truncated-history",
+        output: [{ type: "message", role: "assistant", content: "hello" }],
+      },
+    },
+  });
+
+  assert.equal(store.resolvePreviousResponseState("resp_gen-truncated-history", "key-1"), null);
+});
+
 test("resolvePreviousResponseState returns null when detail logging was never captured for this row", () => {
   insertCallLog({
     id: "log-5",