[codex-analytics] thread events (#15690)

- add event for thread initialization
- thread/start, thread/fork, thread/resume
- feature flagged behind `FeatureFlag::GeneralAnalytics`
- does not yet support threads started by subagents

PR stack:
- --> [[telemetry] thread events
#15690](https://github.com/openai/codex/pull/15690)
- [[telemetry] subagent events
#15915](https://github.com/openai/codex/pull/15915)
- [[telemetry] turn events
#15591](https://github.com/openai/codex/pull/15591)
- [[telemetry] steer events
#15697](https://github.com/openai/codex/pull/15697)
- [[telemetry] queued prompt data
#15804](https://github.com/openai/codex/pull/15804)


Sample extracted logs in Codex-backend
```
INFO     | 2026-03-29 16:39:37 | codex_backend.routers.analytics_events | analytics_events.track_analytics_events:398 | Tracked analytics event codex_thread_initialized thread_id=019d3bf7-9f5f-7f82-9877-6d48d1052531 product_surface=codex product_client_id=CODEX_CLI client_name=codex-tui client_version=0.0.0 rpc_transport=in_process experimental_api_enabled=True codex_rs_version=0.0.0 runtime_os=macos runtime_os_version=26.4.0 runtime_arch=aarch64 model=gpt-5.3-codex ephemeral=False thread_source=user initialization_mode=new subagent_source=None parent_thread_id=None created_at=1774827577 | 
INFO     | 2026-03-29 16:45:46 | codex_backend.routers.analytics_events | analytics_events.track_analytics_events:398 | Tracked analytics event codex_thread_initialized thread_id=019d3b84-5731-79d0-9b3b-9c6efe5f5066 product_surface=codex product_client_id=CODEX_CLI client_name=codex-tui client_version=0.0.0 rpc_transport=in_process experimental_api_enabled=True codex_rs_version=0.0.0 runtime_os=macos runtime_os_version=26.4.0 runtime_arch=aarch64 model=gpt-5.3-codex ephemeral=False thread_source=user initialization_mode=resumed subagent_source=None parent_thread_id=None created_at=1774820022 | 
INFO     | 2026-03-29 16:45:49 | codex_backend.routers.analytics_events | analytics_events.track_analytics_events:398 | Tracked analytics event codex_thread_initialized thread_id=019d3bfd-4cd6-7c12-a13e-48cef02e8c4d product_surface=codex product_client_id=CODEX_CLI client_name=codex-tui client_version=0.0.0 rpc_transport=in_process experimental_api_enabled=True codex_rs_version=0.0.0 runtime_os=macos runtime_os_version=26.4.0 runtime_arch=aarch64 model=gpt-5.3-codex ephemeral=False thread_source=user initialization_mode=forked subagent_source=None parent_thread_id=None created_at=1774827949 | 
INFO     | 2026-03-29 17:20:29 | codex_backend.routers.analytics_events | analytics_events.track_analytics_events:398 | Tracked analytics event codex_thread_initialized thread_id=019d3c1d-0412-7ed2-ad24-c9c0881a36b0 product_surface=codex product_client_id=CODEX_SERVICE_EXEC client_name=codex_exec client_version=0.0.0 rpc_transport=in_process experimental_api_enabled=True codex_rs_version=0.0.0 runtime_os=macos runtime_os_version=26.4.0 runtime_arch=aarch64 model=gpt-5.3-codex ephemeral=False thread_source=user initialization_mode=new subagent_source=None parent_thread_id=None created_at=1774830027 | 
```

Notes
- `product_client_id` gets canonicalized in codex-backend
- subagent threads are addressed in a following pr

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

@@ -26,6 +26,7 @@ use pretty_assertions::assert_eq;
 use serde_json::Value;
 use serde_json::json;
 use std::path::Path;
+use std::time::Duration;
 use tempfile::TempDir;
 use tokio::time::timeout;
 use wiremock::Mock;
@@ -34,6 +35,11 @@ use wiremock::ResponseTemplate;
 use wiremock::matchers::method;
 use wiremock::matchers::path;
 
+use super::analytics::assert_basic_thread_initialized_event;
+use super::analytics::enable_analytics_capture;
+use super::analytics::thread_initialized_event;
+use super::analytics::wait_for_analytics_payload;
+
 const DEFAULT_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10);
 
 #[tokio::test]
@@ -153,6 +159,73 @@ async fn thread_start_creates_thread_and_emits_started() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn thread_start_tracks_thread_initialized_analytics() -> Result<()> {
+    let server = create_mock_responses_server_repeating_assistant("Done").await;
+
+    let codex_home = TempDir::new()?;
+    create_config_toml_with_chatgpt_base_url(
+        codex_home.path(),
+        &server.uri(),
+        &server.uri(),
+        /*general_analytics_enabled*/ true,
+    )?;
+    enable_analytics_capture(&server, codex_home.path()).await?;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
+
+    let req_id = mcp
+        .send_thread_start_request(ThreadStartParams::default())
+        .await?;
+    let resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(req_id)),
+    )
+    .await??;
+    let ThreadStartResponse { thread, .. } = to_response::<ThreadStartResponse>(resp)?;
+
+    let payload = wait_for_analytics_payload(&server, DEFAULT_READ_TIMEOUT).await?;
+    assert_eq!(payload["events"].as_array().expect("events array").len(), 1);
+    let event = thread_initialized_event(&payload)?;
+    assert_basic_thread_initialized_event(event, &thread.id, "mock-model", "new");
+    Ok(())
+}
+
+#[tokio::test]
+async fn thread_start_does_not_track_thread_initialized_analytics_without_feature() -> Result<()> {
+    let server = create_mock_responses_server_repeating_assistant("Done").await;
+
+    let codex_home = TempDir::new()?;
+    create_config_toml_with_chatgpt_base_url(
+        codex_home.path(),
+        &server.uri(),
+        &server.uri(),
+        /*general_analytics_enabled*/ false,
+    )?;
+    enable_analytics_capture(&server, codex_home.path()).await?;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
+
+    let req_id = mcp
+        .send_thread_start_request(ThreadStartParams::default())
+        .await?;
+    let resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(req_id)),
+    )
+    .await??;
+    let _ = to_response::<ThreadStartResponse>(resp)?;
+
+    let payload = wait_for_analytics_payload(&server, Duration::from_millis(250)).await;
+    assert!(
+        payload.is_err(),
+        "thread analytics should be gated off when general_analytics is disabled"
+    );
+    Ok(())
+}
+
 #[tokio::test]
 async fn thread_start_respects_project_config_from_cwd() -> Result<()> {
     let server = create_mock_responses_server_repeating_assistant("Done").await;
@@ -455,6 +528,7 @@ async fn thread_start_surfaces_cloud_requirements_load_errors() -> Result<()> {
         codex_home.path(),
         &model_server.uri(),
         &chatgpt_base_url,
+        /*general_analytics_enabled*/ false,
     )?;
     write_chatgpt_auth(
         codex_home.path(),
@@ -538,7 +612,13 @@ fn create_config_toml_with_chatgpt_base_url(
     codex_home: &Path,
     server_uri: &str,
     chatgpt_base_url: &str,
+    general_analytics_enabled: bool,
 ) -> std::io::Result<()> {
+    let general_analytics_toml = if general_analytics_enabled {
+        "\n[features]\ngeneral_analytics = true\n".to_string()
+    } else {
+        String::new()
+    };
     let config_toml = codex_home.join("config.toml");
     std::fs::write(
         config_toml,
@@ -550,6 +630,7 @@ sandbox_mode = "read-only"
 chatgpt_base_url = "{chatgpt_base_url}"
 
 model_provider = "mock_provider"
+{general_analytics_toml}
 
 [model_providers.mock_provider]
 name = "Mock provider for test"