Detect Codex installs managed by pnpm (#31503)

## Why

The Codex JavaScript shim currently distinguishes npm and Bun installs,
but a global pnpm install falls back to npm. That causes the native CLI,
`codex doctor`, and update flows to report or run npm commands even
though pnpm owns the installation. pnpm also allows its global package
and bin directories to differ, so `PNPM_HOME` does not reliably identify
the package owner.

## What changed

- detect pnpm-managed installs by finding pnpm's
`node_modules/.modules.yaml` metadata from the launched JavaScript
entrypoint
- pass a mutually exclusive `CODEX_MANAGED_BY_PNPM` marker into the
native CLI
- represent pnpm in install context, doctor output, version checks, and
TUI update actions without changing the existing public
`InstallContext::from_exe` signature
- recommend `pnpm add -g @openai/codex` for pnpm-managed installs and
snapshot the rendered TUI update notice

Validated with the 9-test install-context suite, the focused pnpm TUI
snapshot test, and Node's syntax check for the launcher.

Closes https://github.com/openai/codex/issues/10294.

codex-rs/tui/src/history_cell/snapshots/codex_tui__history_cell__tests__pnpm_update_available_history_cell_snapshot.snap

@@ -0,0 +1,11 @@
+---
+source: tui/src/history_cell/tests.rs
+expression: rendered
+---
+╭─────────────────────────────────────────────────╮
+│ ✨ Update available! 0.0.0 -> 9.9.9             │
+│ Run pnpm add -g @openai/codex to update.        │
+│                                                 │
+│ See full release notes:                         │
+│ https://github.com/openai/codex/releases/latest │
+╰─────────────────────────────────────────────────╯

codex-rs/tui/src/history_cell/tests.rs

@@ -1137,6 +1137,15 @@ fn standalone_windows_update_available_history_cell_snapshot() {
     insta::assert_snapshot!(rendered);
 }
 
+#[test]
+fn pnpm_update_available_history_cell_snapshot() {
+    let cell =
+        UpdateAvailableHistoryCell::new("9.9.9".to_string(), Some(UpdateAction::PnpmGlobalLatest));
+    let rendered = render_lines(&cell.display_lines(/*width*/ 110)).join("\n");
+
+    insta::assert_snapshot!(rendered);
+}
+
 #[test]
 fn web_search_history_cell_without_detail_snapshot() {
     let cell = new_web_search_call("call-1".to_string(), String::new(), WebSearchAction::Other);

codex-rs/tui/src/update_action.rs

@@ -12,6 +12,8 @@ pub enum UpdateAction {
     NpmGlobalLatest,
     /// Update via `bun install -g @openai/codex@latest`.
     BunGlobalLatest,
+    /// Update via `pnpm add -g @openai/codex@latest`.
+    PnpmGlobalLatest,
     /// Update via `brew upgrade codex`.
     BrewUpgrade,
     /// Update via `curl -fsSL https://chatgpt.com/codex/install.sh | CODEX_NON_INTERACTIVE=1 sh`.
@@ -26,6 +28,7 @@ impl UpdateAction {
         match &context.method {
             InstallMethod::Npm => Some(UpdateAction::NpmGlobalLatest),
             InstallMethod::Bun => Some(UpdateAction::BunGlobalLatest),
+            InstallMethod::Pnpm => Some(UpdateAction::PnpmGlobalLatest),
             InstallMethod::Brew => Some(UpdateAction::BrewUpgrade),
             InstallMethod::Standalone { platform, .. } => Some(match platform {
                 StandalonePlatform::Unix => UpdateAction::StandaloneUnix,
@@ -40,6 +43,7 @@ impl UpdateAction {
         match self {
             UpdateAction::NpmGlobalLatest => ("npm", &["install", "-g", "@openai/codex"]),
             UpdateAction::BunGlobalLatest => ("bun", &["install", "-g", "@openai/codex"]),
+            UpdateAction::PnpmGlobalLatest => ("pnpm", &["add", "-g", "@openai/codex"]),
             UpdateAction::BrewUpgrade => ("brew", &["upgrade", "--cask", "codex"]),
             UpdateAction::StandaloneUnix => (
                 "sh",
@@ -106,6 +110,13 @@ mod tests {
             }),
             Some(UpdateAction::BunGlobalLatest)
         );
+        assert_eq!(
+            UpdateAction::from_install_context(&InstallContext {
+                method: InstallMethod::Pnpm,
+                package_layout: None,
+            }),
+            Some(UpdateAction::PnpmGlobalLatest)
+        );
         assert_eq!(
             UpdateAction::from_install_context(&InstallContext {
                 method: InstallMethod::Brew,

codex-rs/tui/src/updates.rs

@@ -79,7 +79,9 @@ async fn check_for_update(version_file: &Path, action: Option<UpdateAction>) ->
                 .await?;
             version
         }
-        Some(UpdateAction::NpmGlobalLatest) | Some(UpdateAction::BunGlobalLatest) => {
+        Some(UpdateAction::NpmGlobalLatest)
+        | Some(UpdateAction::BunGlobalLatest)
+        | Some(UpdateAction::PnpmGlobalLatest) => {
             let latest_version = fetch_latest_github_release_version().await?;
             let package_info = create_client()
                 .get(npm_registry::PACKAGE_URL)