diff --git a/apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.test.ts b/apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.test.ts
index e20edf4c5e723..9f51465454ac1 100644
--- a/apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.test.ts
+++ b/apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.test.ts
@@ -7702,6 +7702,121 @@ describe("CodexAdapterV2 post-settle continuation", () => {
     ),
   );
 
+  it.effect("unarchives an unloaded Codex thread before rolling it back", () =>
+    Effect.gen(function* () {
+      const nativeThreadId = "archived-rollback-thread";
+      const resumeParams = {
+        threadId: nativeThreadId,
+        excludeTurns: true,
+        cwd: CODEX_TEST_RUNTIME_POLICY.cwd,
+        model: CODEX_TEST_MODEL_SELECTION.model,
+        config: CodexAdapterV2.CODEX_THREAD_CONFIG,
+      };
+      const thread = codexReplayThreadResult({ nativeThreadId, forkedFromId: null });
+      const exchange = (
+        id: number,
+        method: string,
+        params: unknown,
+        reply: { readonly result: unknown } | { readonly error: unknown },
+      ): Array<CodexReplay.CodexAppServerReplayEntry> => [
+        { type: "expect_outbound", label: method, frame: { id, method, params } },
+        { type: "emit_inbound", label: method, frame: { id, ...reply } },
+      ];
+      const transcript = makeCodexReplayTranscript({
+        scenario: "codex-archived-rollback",
+        entries: [
+          ...codexReplayPreamble({
+            nativeThreadId,
+            nativeTurnId: "archived-rollback-turn",
+            prompt: "unused",
+          }).slice(0, 5),
+          ...exchange(
+            3,
+            "thread/read",
+            { threadId: nativeThreadId, includeTurns: false },
+            {
+              result: {
+                thread: {
+                  id: nativeThreadId,
+                  historyMode: "paginated",
+                  status: { type: "notLoaded" },
+                },
+              },
+            },
+          ),
+          ...exchange(4, "thread/resume", resumeParams, {
+            error: { code: -32600, message: `session ${nativeThreadId} is archived` },
+          }),
+          ...exchange(5, "thread/unarchive", { threadId: nativeThreadId }, { result: thread }),
+          ...exchange(6, "thread/resume", resumeParams, { result: thread }),
+          ...exchange(
+            7,
+            "thread/turns/list",
+            {
+              threadId: nativeThreadId,
+              cursor: null,
+              limit: 1,
+              sortDirection: "desc",
+              itemsView: "summary",
+            },
+            {
+              result: {
+                data: [{ id: "native-turn-second", items: [], status: "completed", error: null }],
+                nextCursor: null,
+              },
+            },
+          ),
+          ...exchange(
+            8,
+            "thread/revert",
+            { threadId: nativeThreadId, beforeTurnId: "native-turn-second" },
+            { result: thread },
+          ),
+        ],
+      });
+      const harness = yield* makeCodexReplayHarness(transcript);
+      const now = yield* DateTime.now;
+      const firstTurn = codexReplaySourceTurn({
+        id: "provider-turn-first",
+        ordinal: 1,
+        nativeId: "native-turn-first",
+        providerThreadId: harness.providerThread.id,
+        now,
+      });
+      const secondTurn = codexReplaySourceTurn({
+        id: "provider-turn-second",
+        ordinal: 2,
+        nativeId: "native-turn-second",
+        providerThreadId: harness.providerThread.id,
+        now,
+      });
+
+      const snapshot = yield* harness.runtime.rollbackThread({
+        providerThread: harness.providerThread,
+        target: {
+          type: "provider_turn",
+          checkpointId: CheckpointId.make("checkpoint-archived-rollback"),
+          appRunOrdinal: 1,
+          providerTurn: firstTurn,
+        },
+        providerThreadTurns: [firstTurn, secondTurn],
+      });
+
+      assert.equal(snapshot.providerThread.nativeThreadRef?.nativeId, nativeThreadId);
+      assert.deepEqual(snapshot.providerThread.nativeConversationHeadRef, firstTurn.nativeTurnRef);
+    }).pipe(
+      Effect.scoped,
+      Effect.provide(
+        Layer.mergeAll(
+          IdAllocator.layer,
+          McpProviderSessions.layer,
+          NodeServices.layer,
+          NodeCrypto.layer,
+        ),
+      ),
+    ),
+  );
+
   it.effect(
     "falls back to fork-local thread/revert on paginated history when the source turn lacks a native reference",
     () =>
diff --git a/apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.ts b/apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.ts
index 277232830676d..b0018be2d0f16 100644
--- a/apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.ts
+++ b/apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.ts
@@ -6696,6 +6696,24 @@ export const makeCodexAdapterV2 = Effect.fn("makeCodexAdapterV2")(function* (
           );
         });
 
+        // Codex refuses to resume a session archived elsewhere until it is unarchived.
+        const resumeNativeThread = Effect.fn("CodexAdapterV2.resumeNativeThread")(function* (
+          threadId: string,
+          params: Record<string, unknown>,
+        ) {
+          const resume = client.raw.request("thread/resume", { threadId, ...params });
+          return yield* resume.pipe(
+            Effect.catchTags({
+              CodexAppServerRequestError: (cause) =>
+                /\bsession \S+ is archived\b|\bcodex unarchive\b/i.test(cause.errorMessage)
+                  ? client.raw
+                      .request("thread/unarchive", { threadId })
+                      .pipe(Effect.andThen(resume))
+                  : Effect.fail(cause),
+            }),
+          );
+        });
+
         const startNativeTurn = Effect.fn("CodexAdapterV2.startNativeTurn")(
           function* (
             turnInput: ProviderAdapter.ProviderAdapterV2TurnInput,
@@ -7048,8 +7066,7 @@ export const makeCodexAdapterV2 = Effect.fn("makeCodexAdapterV2")(function* (
             function* (threadInput) {
               const nativeThreadId = yield* getNativeThreadId(threadInput.providerThread);
               const appThreadId = threadInput.threadId ?? threadInput.providerThread.appThreadId;
-              const resume = client.raw.request("thread/resume", {
-                threadId: nativeThreadId,
+              const resume = resumeNativeThread(nativeThreadId, {
                 excludeTurns: true,
                 ...codexThreadRuntimeParams({
                   threadId: appThreadId,
@@ -7063,24 +7080,7 @@ export const makeCodexAdapterV2 = Effect.fn("makeCodexAdapterV2")(function* (
                 }),
               });
               const response = yield* ensureInitialized.pipe(
-                Effect.andThen(
-                  resume.pipe(
-                    Effect.catchTags({
-                      CodexAppServerRequestError: (cause) => {
-                        if (
-                          !/\bsession \S+ is archived\b|\bcodex unarchive\b/i.test(
-                            cause.errorMessage,
-                          )
-                        ) {
-                          return Effect.fail(cause);
-                        }
-                        return client.raw
-                          .request("thread/unarchive", { threadId: nativeThreadId })
-                          .pipe(Effect.andThen(resume));
-                      },
-                    }),
-                  ),
-                ),
+                Effect.andThen(resume),
                 Effect.flatMap(decodeCodexResumeMetadata),
               );
               return {
@@ -7834,8 +7834,7 @@ export const makeCodexAdapterV2 = Effect.fn("makeCodexAdapterV2")(function* (
               }
               // thread/revert requires the thread loaded in this app-server; resume after restart or idle release.
               if (!loaded) {
-                yield* client.raw.request("thread/resume", {
-                  threadId,
+                yield* resumeNativeThread(threadId, {
                   excludeTurns: true,
                   ...codexThreadRuntimeParams({
                     threadId: threadInput.providerThread.appThreadId,