diff --git a/src/server/request-log-conversation.ts b/src/server/request-log-conversation.ts
index 7cef86ab47..c70f96e27a 100644
--- a/src/server/request-log-conversation.ts
+++ b/src/server/request-log-conversation.ts
@@ -58,7 +58,21 @@ export function matchesLogConversationId(
  * parent thread header > session_id / session-id > thread-id > cursor conversation id.
  */
 export function sessionIdHeaderFromRequest(headers: Headers): string | null {
-  return headers.get("session_id") ?? headers.get("session-id");
+  return firstNonEmptyHeader(headers, "session_id", "session-id");
+}
+
+/** Cursor conversation reuse: Codex parent thread, then Responses session headers. */
+export function clientThreadIdFromResponsesHeaders(headers: Headers): string | undefined {
+  return firstNonEmptyHeader(headers, "x-codex-parent-thread-id", "session_id", "session-id")
+    || undefined;
+}
+
+function firstNonEmptyHeader(headers: Headers, ...names: string[]): string | null {
+  for (const name of names) {
+    const value = headers.get(name)?.trim();
+    if (value) return value;
+  }
+  return null;
 }
 
 export function conversationIdFromResponsesRequest(input: {
diff --git a/src/server/responses/core.ts b/src/server/responses/core.ts
index 2df5160984..2a5ebe7ef5 100644
--- a/src/server/responses/core.ts
+++ b/src/server/responses/core.ts
@@ -173,6 +173,7 @@ import {
   type RequestLogContext,
 } from "../request-log";
 import {
+  clientThreadIdFromResponsesHeaders,
   conversationIdFromResponsesRequest,
   normalizeLogConversationId,
   sessionIdHeaderFromRequest,
@@ -1246,6 +1247,7 @@ export async function handleComboResponses(
   config: OcxConfig,
   logCtx: RequestLogContext,
   options: HandleResponsesOptions,
+  inboundClientThreadId = clientThreadIdFromResponsesHeaders(req.headers),
 ): Promise<Response> {
   const requestedModel = typeof (rawBody as { model?: unknown } | null)?.model === "string"
     ? (rawBody as { model: string }).model
@@ -1263,7 +1265,7 @@ export async function handleComboResponses(
   // Expand previous_response_id before image policy and child dispatch so a
   // continuation that only references prior images still fails closed when
   // imageInput is disabled (and so targets see the full replayed input).
-  const body = expandPreviousResponseInput(rawBody);
+  const body = expandPreviousResponseInput(rawBody, inboundClientThreadId);
   if (previousResponseReplayFailure(body)) {
     return formatErrorResponse(
       400,
@@ -1641,6 +1643,7 @@ async function handleResponsesInner(
     }
     return decodeRequestErrorResponse(err, "responses");
   }
+  const inboundClientThreadId = clientThreadIdFromResponsesHeaders(req.headers);
   const comboId = !options.comboAttempt ? comboIdFromRawBody(body, config) : null;
   if (comboId && Object.hasOwn(config.combos ?? {}, comboId)) {
     options.onRequestBodyRead?.();
@@ -1649,12 +1652,11 @@ async function handleResponsesInner(
       // The original request body was accepted above. Combo children are synthetic
       // replays and must not repeat the caller-owned timeout transition.
       onRequestBodyRead: undefined,
-    });
+    }, inboundClientThreadId);
   }
   let unreadableEncryptedAgentTask = hasUnreadableEncryptedAgentTask(
     (body as { input?: unknown } | undefined)?.input,
   );
-  const inboundClientThreadId = req.headers.get("x-codex-parent-thread-id")?.trim() || undefined;
   const originalBody = body;
   body = expandPreviousResponseInput(body, inboundClientThreadId);
   if (previousResponseScopeMismatch(body)) {
diff --git a/tests/request-log-conversation.test.ts b/tests/request-log-conversation.test.ts
index 0a086498f6..ad18dd51de 100644
--- a/tests/request-log-conversation.test.ts
+++ b/tests/request-log-conversation.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "bun:test";
 import { createHash } from "node:crypto";
 import {
+  clientThreadIdFromResponsesHeaders,
   conversationIdFromClaudeCacheKey,
   conversationIdFromClaudeMetadata,
   conversationIdFromResponsesRequest,
@@ -68,6 +69,32 @@ describe("sessionIdHeaderFromRequest", () => {
       session_id: "underscore",
       "session-id": "hyphen",
     }))).toBe("underscore");
+    expect(sessionIdHeaderFromRequest(new Headers({
+      session_id: "   ",
+      "session-id": "hyphen",
+    }))).toBe("hyphen");
+  });
+});
+
+describe("clientThreadIdFromResponsesHeaders", () => {
+  test("prefers Codex parent thread over session_id", () => {
+    expect(clientThreadIdFromResponsesHeaders(new Headers({
+      "x-codex-parent-thread-id": "parent",
+      session_id: "session",
+    }))).toBe("parent");
+  });
+
+  test("falls back to session_id so store:false clients reuse Cursor conversations", () => {
+    expect(clientThreadIdFromResponsesHeaders(new Headers({
+      session_id: "gjc-session",
+    }))).toBe("gjc-session");
+  });
+
+  test("falls back to session-id when session_id is blank", () => {
+    expect(clientThreadIdFromResponsesHeaders(new Headers({
+      session_id: "   ",
+      "session-id": "hyphen-session",
+    }))).toBe("hyphen-session");
   });
 });