diff --git a/packages/paperclip-runner/runner/crates/runner-core/src/bin/fake-codex-app-server.rs b/packages/paperclip-runner/runner/crates/runner-core/src/bin/fake-codex-app-server.rs
index 3490a4c1b08..18059de632f 100644
--- a/packages/paperclip-runner/runner/crates/runner-core/src/bin/fake-codex-app-server.rs
+++ b/packages/paperclip-runner/runner/crates/runner-core/src/bin/fake-codex-app-server.rs
@@ -1619,56 +1619,71 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
                         }))?;
                     }
                     if emit_post_completion_passive_statuses {
-                        if let Some(gate) = post_completion_notification_gate.as_ref() {
-                            let deadline = std::time::Instant::now() + Duration::from_secs(5);
-                            while !gate.is_file() {
-                                if std::time::Instant::now() >= deadline {
-                                    return Err(
-                                        "post-completion notification gate timed out".into()
-                                    );
+                        let gate = post_completion_notification_gate.clone();
+                        let thread_id = state.thread_id.clone();
+                        let tail_turn_id = provider_turn_id.clone();
+                        // Goal reconciliation reads must remain responsive while
+                        // the test holds back the post-terminal passive notices.
+                        thread::spawn(move || {
+                            let result = (|| -> io::Result<()> {
+                                if let Some(gate) = gate.as_ref() {
+                                    let deadline =
+                                        std::time::Instant::now() + Duration::from_secs(5);
+                                    while !gate.is_file() {
+                                        if std::time::Instant::now() >= deadline {
+                                            return Err(io::Error::new(
+                                                io::ErrorKind::TimedOut,
+                                                "post-completion notification gate timed out",
+                                            ));
+                                        }
+                                        thread::sleep(Duration::from_millis(1));
+                                    }
                                 }
-                                thread::sleep(Duration::from_millis(1));
+                                for notification in [
+                                    json!({
+                                        "method": "deprecationNotice",
+                                        "params": {"summary": "A provider setting is deprecated", "details": null}
+                                    }),
+                                    json!({
+                                        "method": "remoteControl/status/changed",
+                                        "params": {"status": "disabled", "environmentId": null}
+                                    }),
+                                    json!({
+                                        "method": "mcpServer/startupStatus/updated",
+                                        "params": {"name": "codex_apps", "status": "ready", "error": null}
+                                    }),
+                                    json!({
+                                        "method": "account/rateLimits/updated",
+                                        "params": {"rateLimits": {}}
+                                    }),
+                                    json!({
+                                        "method": "rawResponseItem/completed",
+                                        "params": {"threadId": thread_id, "turnId": tail_turn_id, "item": {"id": "raw-tail", "type": "reasoning"}}
+                                    }),
+                                    json!({
+                                        "method": "rawResponse/completed",
+                                        "params": {"threadId": thread_id, "turnId": tail_turn_id, "response": {"id": "response-tail"}}
+                                    }),
+                                    json!({
+                                        "method": "thread/goal/updated",
+                                        "params": {"threadId": thread_id, "goal": "finish the turn"}
+                                    }),
+                                    json!({
+                                        "method": "thread/goal/cleared",
+                                        "params": {"threadId": thread_id}
+                                    }),
+                                ] {
+                                    send(notification)?;
+                                }
+                                if let Some(gate) = gate.as_ref() {
+                                    fs::write(gate.with_extension("emitted"), b"emitted")?;
+                                }
+                                Ok(())
+                            })();
+                            if let Err(error) = result {
+                                eprintln!("post-completion passive tail failed: {error}");
                             }
-                        }
-                        for notification in [
-                            json!({
-                                "method": "deprecationNotice",
-                                "params": {"summary": "A provider setting is deprecated", "details": null}
-                            }),
-                            json!({
-                                "method": "remoteControl/status/changed",
-                                "params": {"status": "disabled", "environmentId": null}
-                            }),
-                            json!({
-                                "method": "mcpServer/startupStatus/updated",
-                                "params": {"name": "codex_apps", "status": "ready", "error": null}
-                            }),
-                            json!({
-                                "method": "account/rateLimits/updated",
-                                "params": {"rateLimits": {}}
-                            }),
-                            json!({
-                                "method": "rawResponseItem/completed",
-                                "params": {"threadId": state.thread_id, "turnId": provider_turn_id, "item": {"id": "raw-tail", "type": "reasoning"}}
-                            }),
-                            json!({
-                                "method": "rawResponse/completed",
-                                "params": {"threadId": state.thread_id, "turnId": provider_turn_id, "response": {"id": "response-tail"}}
-                            }),
-                            json!({
-                                "method": "thread/goal/updated",
-                                "params": {"threadId": state.thread_id, "goal": "finish the turn"}
-                            }),
-                            json!({
-                                "method": "thread/goal/cleared",
-                                "params": {"threadId": state.thread_id}
-                            }),
-                        ] {
-                            send(notification)?;
-                        }
-                        if let Some(gate) = post_completion_notification_gate.as_ref() {
-                            fs::write(gate.with_extension("emitted"), b"emitted")?;
-                        }
+                        });
                     }
                     if emit_post_completion_foreign_turn {
                         let gate = post_completion_notification_gate.clone();
diff --git a/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.test.ts b/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.test.ts
index 45ad16975f5..9ebcda1bd6c 100644
--- a/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.test.ts
+++ b/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.test.ts
@@ -101,7 +101,10 @@ describe("Codex ACPX runtime adapter", () => {
     });
   });
 
-  it.each([["claude" as const, "claude-sonnet-5", "claude-sonnet-5"]])(
+  it.each([
+    ["claude" as const, "claude-sonnet-5", "claude-sonnet-5"],
+    ["claude" as const, "custom-claude-model", "custom-claude-model"],
+  ])(
     "opens the qualified %s session through the verified lease",
     async (agent, model, providerModel) => {
       const runtime = fakeRuntime();
@@ -109,7 +112,7 @@ describe("Codex ACPX runtime adapter", () => {
       const options = openOptions(command);
       let runtimeOptions: AcpRuntimeOptions | undefined;
       options.profile = resolveQualifiedAcpxProfile(agent, model);
-      options.launchEnvironment = { PATH: "/verified/bin" };
+      options.launchEnvironment = { PATH: "/verified/bin", ANTHROPIC_CUSTOM_MODEL_OPTION: "stale-model" };
 
       await openCodexAcpxRuntime(options, {
         createRegistry: ({ overrides }) => {
@@ -128,6 +131,7 @@ describe("Codex ACPX runtime adapter", () => {
       expect(runtimeOptions?.spawnEnvironment?.()).toEqual({
         PATH: "/verified/bin",
         PAPERCLIP_ACPX_ISOLATED_CONTEXT: "1",
+        ANTHROPIC_CUSTOM_MODEL_OPTION: providerModel,
       });
       expect(runtime.ensureSession).toHaveBeenCalledWith(
         expect.objectContaining({
diff --git a/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.ts b/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.ts
index b92419eec63..a5c1d2d456f 100644
--- a/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.ts
+++ b/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.ts
@@ -317,7 +317,14 @@ export async function openQualifiedAcpxRuntime(
     spawnEnvironment: () => ({
       ...definedEnvironment(options.launchEnvironment),
       ...(options.profile.agent === "claude"
-        ? { PAPERCLIP_ACPX_ISOLATED_CONTEXT: "1" }
+        ? {
+            PAPERCLIP_ACPX_ISOLATED_CONTEXT: "1",
+            // Claude ACP otherwise maps concrete IDs back to rolling picker
+            // aliases (e.g. claude-sonnet-5 -> sonnet). Advertise the exact
+            // host-requested ID so model verification stays exact on resume
+            // and before the first billable prompt.
+            ANTHROPIC_CUSTOM_MODEL_OPTION: options.profile.reportedModelId,
+          }
         : {}),
     }),
     spawnCwd: options.cwd,