notify: include client in legacy hook payload (#12968)

## Why

The `notify` hook payload did not identify which Codex client started
the turn. That meant downstream notification hooks could not distinguish
between completions coming from the TUI and completions coming from
app-server clients such as VS Code or Xcode. Now that the Codex App
provides its own desktop notifications, it would be nice to be able to
filter those out.

This change adds that context without changing the existing payload
shape for callers that do not know the client name, and keeps the new
end-to-end test cross-platform.

## What changed

- added an optional top-level `client` field to the legacy `notify` JSON
payload
- threaded that value through `core` and `hooks`; the internal session
and turn state now carries it as `app_server_client_name`
- set the field to `codex-tui` for TUI turns
- captured `initialize.clientInfo.name` in the app server and applied it
to subsequent turns before dispatching hooks
- replaced the notify integration test hook with a `python3` script so
the test does not rely on Unix shell permissions or `bash`
- documented the new field in `docs/config.md`

## Testing

- `cargo test -p codex-hooks`
- `cargo test -p codex-tui`
- `cargo test -p codex-app-server
suite::v2::initialize::turn_start_notify_payload_includes_initialize_client_name
-- --exact --nocapture`
- `cargo test -p codex-core` (`src/lib.rs` passed; `core/tests/all.rs`
still has unrelated existing failures in this environment)

## Docs

The public config reference on `developers.openai.com/codex` should
mention that the legacy `notify` payload may include a top-level
`client` field. The TUI reports `codex-tui`, and the app server reports
`initialize.clientInfo.name` when it is available.

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

@@ -1,16 +1,24 @@
 use anyhow::Result;
 use app_test_support::McpProcess;
+use app_test_support::create_final_assistant_message_sse_response;
 use app_test_support::create_mock_responses_server_sequence_unchecked;
 use app_test_support::to_response;
 use codex_app_server_protocol::ClientInfo;
 use codex_app_server_protocol::InitializeCapabilities;
 use codex_app_server_protocol::InitializeResponse;
 use codex_app_server_protocol::JSONRPCMessage;
+use codex_app_server_protocol::JSONRPCResponse;
 use codex_app_server_protocol::RequestId;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
+use codex_app_server_protocol::TurnStartParams;
+use codex_app_server_protocol::TurnStartResponse;
+use codex_app_server_protocol::UserInput as V2UserInput;
+use core_test_support::fs_wait;
 use pretty_assertions::assert_eq;
+use serde_json::Value;
 use std::path::Path;
+use std::time::Duration;
 use tempfile::TempDir;
 use tokio::time::timeout;
 
@@ -178,11 +186,100 @@ async fn initialize_opt_out_notification_methods_filters_notifications() -> Resu
     Ok(())
 }
 
+#[tokio::test]
+async fn turn_start_notify_payload_includes_initialize_client_name() -> Result<()> {
+    let responses = vec![create_final_assistant_message_sse_response("Done")?];
+    let server = create_mock_responses_server_sequence_unchecked(responses).await;
+    let codex_home = TempDir::new()?;
+    let notify_script = codex_home.path().join("notify.py");
+    std::fs::write(
+        &notify_script,
+        r#"from pathlib import Path
+import sys
+
+Path(__file__).with_name("notify.json").write_text(sys.argv[-1], encoding="utf-8")
+"#,
+    )?;
+    let notify_file = codex_home.path().join("notify.json");
+    let notify_script = notify_script
+        .to_str()
+        .expect("notify script path should be valid UTF-8");
+    create_config_toml_with_extra(
+        codex_home.path(),
+        &server.uri(),
+        "never",
+        &format!(
+            "notify = [\"python3\", {}]",
+            toml_basic_string(notify_script)
+        ),
+    )?;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.initialize_with_client_info(ClientInfo {
+            name: "xcode".to_string(),
+            title: Some("Xcode".to_string()),
+            version: "1.0.0".to_string(),
+        }),
+    )
+    .await??;
+
+    let thread_req = mcp
+        .send_thread_start_request(ThreadStartParams::default())
+        .await?;
+    let thread_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(thread_req)),
+    )
+    .await??;
+    let ThreadStartResponse { thread, .. } = to_response(thread_resp)?;
+
+    let turn_req = mcp
+        .send_turn_start_request(TurnStartParams {
+            thread_id: thread.id,
+            input: vec![V2UserInput::Text {
+                text: "Hello".to_string(),
+                text_elements: Vec::new(),
+            }],
+            ..Default::default()
+        })
+        .await?;
+    let turn_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(turn_req)),
+    )
+    .await??;
+    let _: TurnStartResponse = to_response(turn_resp)?;
+
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("turn/completed"),
+    )
+    .await??;
+
+    fs_wait::wait_for_path_exists(&notify_file, Duration::from_secs(5)).await?;
+    let payload_raw = tokio::fs::read_to_string(&notify_file).await?;
+    let payload: Value = serde_json::from_str(&payload_raw)?;
+    assert_eq!(payload["client"], "xcode");
+
+    Ok(())
+}
+
 // Helper to create a config.toml pointing at the mock model server.
 fn create_config_toml(
     codex_home: &Path,
     server_uri: &str,
     approval_policy: &str,
+) -> std::io::Result<()> {
+    create_config_toml_with_extra(codex_home, server_uri, approval_policy, "")
+}
+
+fn create_config_toml_with_extra(
+    codex_home: &Path,
+    server_uri: &str,
+    approval_policy: &str,
+    extra: &str,
 ) -> std::io::Result<()> {
     let config_toml = codex_home.join("config.toml");
     std::fs::write(
@@ -195,6 +292,8 @@ sandbox_mode = "read-only"
 
 model_provider = "mock_provider"
 
+{extra}
+
 [model_providers.mock_provider]
 name = "Mock provider for test"
 base_url = "{server_uri}/v1"
@@ -205,3 +304,7 @@ stream_max_retries = 0
         ),
     )
 }
+
+fn toml_basic_string(value: &str) -> String {
+    format!("\"{}\"", value.replace('\\', "\\\\").replace('"', "\\\""))
+}