Reject sessions with unloadable required managed hooks (#38394)

## Why

Hooks supplied as managed requirements must not be silently skipped when their
handlers cannot be loaded.

## What changed

- Fail session and app-server thread startup when an enabled managed requirement
  contains an invalid matcher, an empty command, or an unsupported handler type.
- Keep load failures for ordinary managed configuration hooks as warnings, and do
  not enforce managed hook requirements while the hooks feature is disabled.

## Testing

Added hook-engine, core session, and app-server coverage for valid and invalid
managed hook requirements.

GitOrigin-RevId: 91a23b0c1d85e143aba6aabe874c5274e52fc6b2

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

@@ -1083,6 +1083,87 @@ async fn thread_start_fails_when_required_mcp_server_fails_to_initialize() -> Re
     Ok(())
 }
 
+#[tokio::test]
+async fn thread_start_fails_when_managed_hook_matcher_is_invalid() -> Result<()> {
+    let server = create_mock_responses_server_repeating_assistant("Done").await;
+    let codex_home = TempDir::new()?;
+    create_config_toml_without_approval_policy(codex_home.path(), &server.uri())?;
+    std::fs::write(
+        codex_home.path().join("requirements.toml"),
+        r#"[hooks]
+
+[[hooks.PreToolUse]]
+matcher = "["
+
+[[hooks.PreToolUse.hooks]]
+type = "command"
+command = "echo managed"
+"#,
+    )?;
+
+    let mut app_server = TestAppServer::builder()
+        .with_codex_home(codex_home.path())
+        .build_initialized()
+        .await?;
+    let request_id = app_server
+        .send_thread_start_request_with_auto_env(ThreadStartParams::default())
+        .await?;
+    let error: JSONRPCError = timeout(
+        DEFAULT_READ_TIMEOUT,
+        app_server.read_stream_until_error_message(RequestId::Integer(request_id)),
+    )
+    .await??;
+
+    assert!(
+        error.error.message.contains("managed") && error.error.message.contains("invalid matcher"),
+        "unexpected error message: {}",
+        error.error.message
+    );
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn thread_start_fails_when_managed_hook_handler_is_unsupported() -> Result<()> {
+    let server = create_mock_responses_server_repeating_assistant("Done").await;
+    let codex_home = TempDir::new()?;
+    create_config_toml_without_approval_policy(codex_home.path(), &server.uri())?;
+    std::fs::write(
+        codex_home.path().join("requirements.toml"),
+        r#"[hooks]
+
+[[hooks.PreToolUse]]
+matcher = "^Bash$"
+
+[[hooks.PreToolUse.hooks]]
+type = "mcp_tool"
+server = "security"
+tool = "scan"
+"#,
+    )?;
+
+    let mut app_server = TestAppServer::builder()
+        .with_codex_home(codex_home.path())
+        .build_initialized()
+        .await?;
+    let request_id = app_server
+        .send_thread_start_request_with_auto_env(ThreadStartParams::default())
+        .await?;
+    let error: JSONRPCError = timeout(
+        DEFAULT_READ_TIMEOUT,
+        app_server.read_stream_until_error_message(RequestId::Integer(request_id)),
+    )
+    .await??;
+
+    assert!(
+        error.error.message.contains("MCP tool hook"),
+        "unexpected error message: {}",
+        error.error.message
+    );
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn thread_start_emits_mcp_server_status_updated_notifications() -> Result<()> {
     let server = create_mock_responses_server_repeating_assistant("Done").await;