diff --git a/apps/server/src/provider/Drivers/CodexHomeLayout.test.ts b/apps/server/src/provider/Drivers/CodexHomeLayout.test.ts
index 093777e67db5d..2bbcea20faa91 100644
--- a/apps/server/src/provider/Drivers/CodexHomeLayout.test.ts
+++ b/apps/server/src/provider/Drivers/CodexHomeLayout.test.ts
@@ -121,8 +121,10 @@ it.layer(NodeServices.layer)("CodexHomeLayout", (it) => {
             '{"models":["shared"]}\n',
           );
           yield* writeTextFile(path.join(sharedHome, "auth.json"), '{"shared":true}\n');
+          yield* writeTextFile(path.join(sharedHome, "auth.lock"), "");
           yield* fileSystem.makeDirectory(shadowHome, { recursive: true });
           yield* writeTextFile(path.join(shadowHome, "auth.json"), '{"shadow":true}\n');
+          yield* writeTextFile(path.join(shadowHome, "auth.lock"), "");
           yield* fileSystem.symlink(
             path.join(sharedHome, "models_cache.json"),
             path.join(shadowHome, "models_cache.json"),
@@ -149,6 +151,9 @@ it.layer(NodeServices.layer)("CodexHomeLayout", (it) => {
             .readLink(path.join(shadowHome, "auth.json"))
             .pipe(Effect.result);
           const authContents = yield* fileSystem.readFileString(path.join(shadowHome, "auth.json"));
+          const authLockLinkResult = yield* fileSystem
+            .readLink(path.join(shadowHome, "auth.lock"))
+            .pipe(Effect.result);
 
           expect(sessionsTarget).toBe(path.join(sharedHome, "sessions"));
           expect(configTarget).toBe(path.join(sharedHome, "config.toml"));
@@ -156,6 +161,7 @@ it.layer(NodeServices.layer)("CodexHomeLayout", (it) => {
           expect(modelsCacheExists).toBe(false);
           expect(authLinkResult._tag).toBe("Failure");
           expect(authContents).toContain("shadow");
+          expect(authLockLinkResult._tag).toBe("Failure");
         }),
     );
 
@@ -221,6 +227,40 @@ it.layer(NodeServices.layer)("CodexHomeLayout", (it) => {
         }),
     );
 
+    it.effect.skipIf(!symlinksSupported)(
+      "shares local thread writer locks once no writer still holds one",
+      () =>
+        Effect.gen(function* () {
+          const fileSystem = yield* FileSystem.FileSystem;
+          const path = yield* Path.Path;
+          const sharedHome = yield* makeTempDir("t3code-codex-shared-");
+          const shadowRoot = yield* makeTempDir("t3code-codex-shadow-root-");
+          const shadowHome = path.join(shadowRoot, "shadow");
+          const shadowLocks = path.join(shadowHome, "thread-writer-locks");
+          const threadLock = path.join(shadowLocks, "019a0000-0000-7000-8000-000000000000.lock");
+
+          yield* writeTextFile(path.join(shadowLocks, ".coordination.lock"), "");
+          yield* writeTextFile(path.join(shadowLocks, ".DS_Store"), "");
+          yield* writeTextFile(threadLock, "");
+
+          const layout = yield* resolveCodexHomeLayout(
+            decodeCodexSettings({
+              homePath: sharedHome,
+              shadowHomePath: shadowHome,
+            }),
+          );
+
+          yield* materializeCodexShadowHome(layout);
+          expect(yield* fileSystem.exists(threadLock)).toBe(true);
+
+          yield* fileSystem.remove(threadLock);
+          yield* materializeCodexShadowHome(layout);
+          expect(yield* fileSystem.readLink(shadowLocks)).toBe(
+            path.join(sharedHome, "thread-writer-locks"),
+          );
+        }),
+    );
+
     it.effect.skipIf(!symlinksSupported)(
       "accepts Codex-created shadow-local runtime directories",
       () =>
diff --git a/apps/server/src/provider/Drivers/CodexHomeLayout.ts b/apps/server/src/provider/Drivers/CodexHomeLayout.ts
index f175a0fdd00a9..f6d2ba9d44cf5 100644
--- a/apps/server/src/provider/Drivers/CodexHomeLayout.ts
+++ b/apps/server/src/provider/Drivers/CodexHomeLayout.ts
@@ -26,13 +26,19 @@ const KNOWN_SHARED_DIRECTORIES = [
   "cache",
   "logs",
   "mcp-oauth-locks",
+  "thread-writer-locks",
 ] as const;
 
-const PRIVATE_ENTRY_NAMES = new Set(["auth.json", "models_cache.json"]);
+// auth.lock guards the shadow home's private auth.json.
+const PRIVATE_ENTRY_NAMES = new Set(["auth.json", "auth.lock", "models_cache.json"]);
 // Finder maintains metadata separately for each directory, including shadow homes.
 const SHADOW_LOCAL_ENTRY_NAMES = new Set(["log", "memories", "tmp", ".DS_Store"]);
 // Shadow homes may create local runtime locks first; replace them with shared links because they guard shared state.
-const REPLACEABLE_SHARED_RUNTIME_ENTRIES = new Set(["mcp-oauth-locks", ".sqlite-maintenance.lock"]);
+const REPLACEABLE_SHARED_RUNTIME_ENTRIES = new Set([
+  "mcp-oauth-locks",
+  "thread-writer-locks",
+  ".sqlite-maintenance.lock",
+]);
 
 function resolveHomePath(path: Path.Path, home: string, value: string | undefined): string {
   const expanded =
@@ -253,6 +259,30 @@ const ensureSymlink = Effect.fn("CodexHomeLayout.ensureSymlink")(function* (inpu
       });
     }
 
+    if (input.entryName === "thread-writer-locks") {
+      const lockNames = yield* input.fileSystem.readDirectory(link).pipe(
+        Effect.catchTags({
+          PlatformError: (cause) =>
+            new CodexShadowHomeFileSystemError({
+              sharedHomePath: input.sharedHomePath,
+              effectiveHomePath: input.effectiveHomePath,
+              operation: "readDirectory",
+              path: link,
+              entryName: input.entryName,
+              cause,
+            }),
+        }),
+      );
+      // Codex deletes a thread lock on release, so one that is left may still guard a live
+      // writer. Keep the local directory until a later setup finds none.
+      if (lockNames.some((name) => name.endsWith(".lock") && name !== ".coordination.lock")) {
+        return yield* Effect.logWarning(
+          "Codex shadow home still has thread writer locks; it will share them on a later setup.",
+          { path: link },
+        );
+      }
+    }
+
     yield* input.fileSystem.remove(link, { recursive: true }).pipe(
       Effect.catchTags({
         PlatformError: (cause) =>