Materialize rollout state on-demand for v2 thread APIs

### Change summary

Defer rollout file creation until needed.
* Add a core API to force rollout persistence for loaded non-ephemeral threads:
* seeds initial context if needed
* flushes rollout and returns persisted path

Add concurrency guard to make lazy rollout initialization idempotent under concurrent calls.

Add centralized app-server rollout-path resolver that:
* uses in-memory thread state when loaded
* forces persistence on demand for rollout-dependent calls
* falls back to on-disk lookup for unloaded threads
* maps ephemeral threads to invalid-request errors for rollout-dependent operations

Route rollout-dependent endpoints through the resolver (v2 + shared legacy surfaces), including:
* thread/archive
* thread/resume (thread-id path)
* thread/fork (thread-id path)
* resumeConversation
* forkConversation
* thread summary by thread id
* detached review parent-thread path resolution
* feedback include_logs rollout resolution

Remove stale cached rollout-path assumptions in rollback/detached-review flows by resolving via thread id when needed.

No wire-schema changes; behavior-only change.

v1 compatibility is not expanded in this PR.

### Tests updated/added

* thread_start: assert rollout is absent immediately after thread/start; created after first completed turn.
* thread_resume: resume by thread id succeeds for just-started thread via on-demand persistence; path-vs-thread-id precedence test updated.
* thread_fork: fork by thread id succeeds for just-started thread.
* thread_archive: archive succeeds for just-started thread and materializes before archive.
* thread_unarchive: adjusted for deferred creation timing.
* thread_rollback: rollback path no longer depends on stale cached rollout path.
* Detached review targeted test verified for lazy path behavior.
* Core tests for new persistence API

codex-rs/app-server/tests/suite/v2/thread_unarchive.rs

@@ -1,6 +1,8 @@
 use anyhow::Result;
 use app_test_support::McpProcess;
+use app_test_support::create_mock_responses_server_repeating_assistant;
 use app_test_support::to_response;
+use codex_app_server_protocol::JSONRPCNotification;
 use codex_app_server_protocol::JSONRPCResponse;
 use codex_app_server_protocol::RequestId;
 use codex_app_server_protocol::ThreadArchiveParams;
@@ -9,6 +11,8 @@ use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
 use codex_app_server_protocol::ThreadUnarchiveParams;
 use codex_app_server_protocol::ThreadUnarchiveResponse;
+use codex_app_server_protocol::TurnStartParams;
+use codex_app_server_protocol::UserInput;
 use codex_core::find_archived_thread_path_by_id_str;
 use codex_core::find_thread_path_by_id_str;
 use std::fs::FileTimes;
@@ -24,7 +28,8 @@ const DEFAULT_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs
 #[tokio::test]
 async fn thread_unarchive_moves_rollout_back_into_sessions_directory() -> Result<()> {
     let codex_home = TempDir::new()?;
-    create_config_toml(codex_home.path())?;
+    let server = create_mock_responses_server_repeating_assistant("Done").await;
+    create_config_toml(codex_home.path(), &server.uri())?;
 
     let mut mcp = McpProcess::new(codex_home.path()).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -42,6 +47,27 @@ async fn thread_unarchive_moves_rollout_back_into_sessions_directory() -> Result
     .await??;
     let ThreadStartResponse { thread, .. } = to_response::<ThreadStartResponse>(start_resp)?;
 
+    let turn_id = mcp
+        .send_turn_start_request(TurnStartParams {
+            thread_id: thread.id.clone(),
+            input: vec![UserInput::Text {
+                text: "hello".to_string(),
+                text_elements: Vec::new(),
+            }],
+            ..Default::default()
+        })
+        .await?;
+    let _: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(turn_id)),
+    )
+    .await??;
+    let _: JSONRPCNotification = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("turn/completed"),
+    )
+    .await??;
+
     let rollout_path = find_thread_path_by_id_str(codex_home.path(), &thread.id)
         .await?
         .expect("expected rollout path for thread id to exist");
@@ -108,14 +134,25 @@ async fn thread_unarchive_moves_rollout_back_into_sessions_directory() -> Result
     Ok(())
 }
 
-fn create_config_toml(codex_home: &Path) -> std::io::Result<()> {
+fn create_config_toml(codex_home: &Path, server_uri: &str) -> std::io::Result<()> {
     let config_toml = codex_home.join("config.toml");
-    std::fs::write(config_toml, config_contents())
+    std::fs::write(config_toml, config_contents(server_uri))
 }
 
-fn config_contents() -> &'static str {
-    r#"model = "mock-model"
+fn config_contents(server_uri: &str) -> String {
+    format!(
+        r#"model = "mock-model"
 approval_policy = "never"
 sandbox_mode = "read-only"
+
+model_provider = "mock_provider"
+
+[model_providers.mock_provider]
+name = "Mock provider for test"
+base_url = "{server_uri}/v1"
+wire_api = "responses"
+request_max_retries = 0
+stream_max_retries = 0
 "#
+    )
 }