diff --git a/apps/server/src/orchestration-v2/testkit/ProviderSwitch.integration.test.ts b/apps/server/src/orchestration-v2/testkit/ProviderSwitch.integration.test.ts
index 6ec386582170..6e363df5f1dd 100644
--- a/apps/server/src/orchestration-v2/testkit/ProviderSwitch.integration.test.ts
+++ b/apps/server/src/orchestration-v2/testkit/ProviderSwitch.integration.test.ts
@@ -2543,6 +2543,7 @@ describe("orchestration v2 provider switching", () => {
       Effect.gen(function* () {
         const cwd = yield* checkpointWorkspace("provider-switch");
         const capturedTurns = yield* Ref.make<ReadonlyArray<CapturedTurn>>([]);
+        const codexNativeThreadGeneration = yield* Ref.make(0);
         const registryLayer = makeProviderAdapterRegistryLayer([
           makeTestAdapter({
             instanceId: ProviderInstanceId.make("codex"),
@@ -2555,6 +2556,7 @@ describe("orchestration v2 provider switching", () => {
             },
             capturedTurns,
             failResume: true,
+            nativeThreadGeneration: codexNativeThreadGeneration,
           }),
           makeTestAdapter({
             instanceId: ProviderInstanceId.make("claudeAgent"),
@@ -2629,6 +2631,20 @@ describe("orchestration v2 provider switching", () => {
             CLAUDE_MODEL_SELECTION,
           );
           yield* waitForIdle(threadId);
+          // Stopping the shared Codex process drops its loaded native thread, so
+          // returning to Codex has to resume it (and fall back when that fails).
+          const codexSession = (yield* orchestrator.getThreadProjection(
+            threadId,
+          )).providerSessions.find(
+            (session) => session.providerInstanceId === CODEX_MODEL_SELECTION.instanceId,
+          )!;
+          yield* orchestrator.dispatch({
+            type: "provider-session.detach",
+            commandId: CommandId.make("command:provider-switch:stop-codex"),
+            threadId,
+            providerSessionId: codexSession.id,
+          });
+          yield* (yield* OrchestrationEffectWorkerV2).drain();
           yield* orchestrator.dispatch(commands[3]!);
           assert.deepEqual(
             (yield* orchestrator.getThreadProjection(threadId)).thread.modelSelection,
@@ -2667,9 +2683,24 @@ describe("orchestration v2 provider switching", () => {
         assert.lengthOf(projection.providerThreads, 2);
         assert.equal(projection.runs[0]?.providerThreadId, projection.runs[2]?.providerThreadId);
         assert.notEqual(projection.runs[0]?.providerThreadId, projection.runs[1]?.providerThreadId);
+        // The failed resume bound a fresh native Codex thread to the same row.
+        assert.equal(yield* Ref.get(codexNativeThreadGeneration), 2);
+        const codexThread = projection.providerThreads.find(
+          (providerThread) => providerThread.id === projection.runs[2]?.providerThreadId,
+        );
+        assert.equal(codexThread?.nativeThreadRef?.nativeId, `codex:${threadId}:1`);
         assert.deepEqual(
-          projection.contextHandoffs.map((handoff) => handoff.strategy),
-          ["full_thread_summary", "delta_since_target_last_seen"],
+          projection.contextHandoffs.map((handoff) => [
+            handoff.strategy,
+            handoff.coveredRunOrdinals,
+            handoff.delivery?.status,
+            handoff.delivery?.nativeThreadId,
+          ]),
+          [
+            ["full_thread_summary", { from: 1, to: 1 }, "inline", `claudeAgent:${threadId}`],
+            ["delta_since_target_last_seen", { from: 2, to: 2 }, "inline", `codex:${threadId}:1`],
+            ["full_thread_summary", { from: 1, to: 2 }, "inline", `codex:${threadId}:1`],
+          ],
         );
         assert.deepEqual(
           projection.contextTransfers.map((transfer) => [
@@ -2680,6 +2711,7 @@ describe("orchestration v2 provider switching", () => {
           [
             ["provider_handoff", "consumed", "portable_context"],
             ["provider_handoff", "consumed", "delta_context"],
+            ["provider_handoff", "resolved_portable", "portable_context"],
           ],
         );
         assert.deepEqual(
@@ -2703,10 +2735,13 @@ describe("orchestration v2 provider switching", () => {
         assert.include(turns[1]?.text ?? "", "Context handoff (full_thread_summary):");
         assert.include(turns[1]?.text ?? "", "codex before switch");
         assert.include(turns[1]?.text ?? "", claudePrompt);
+        // The fresh native thread has none of the earlier Codex turn, so the
+        // portable fallback re-sends it alongside the Claude delta.
+        assert.include(turns[2]?.text ?? "", "Context handoff (full_thread_summary):");
         assert.include(turns[2]?.text ?? "", "Context handoff (delta_since_target_last_seen):");
+        assert.include(turns[2]?.text ?? "", "codex before switch");
         assert.include(turns[2]?.text ?? "", "claude switched response");
         assert.include(turns[2]?.text ?? "", returnPrompt);
-        assert.notInclude(turns[2]?.text ?? "", "codex before switch");
         assert.equal(turns[0]?.providerThreadId, turns[2]?.providerThreadId);
       }),
     ),