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/cli/src/doctor/output.rs

@@ -1260,7 +1260,7 @@ Environment
       LESS                     -FRX
   ✓ runtime      running local build on darwin-arm64
   ✓ install      consistent
-      managed by               npm: no · bun: no · package root —
+      managed by               npm: no · bun: no · pnpm: no · package root —
   ✓ search       search is OK (bundled)
   ✓ git          git version 2.54.0
       selected git             /usr/bin/git

codex-rs/cli/src/doctor/output/detail.rs

@@ -211,13 +211,15 @@ fn install_details(parsed: &[ParsedDetail], options: HumanOutputOptions) -> Vec<
 
     let managed_by_npm = value(parsed, "managed by npm").unwrap_or("false");
     let managed_by_bun = value(parsed, "managed by bun").unwrap_or("false");
+    let managed_by_pnpm = value(parsed, "managed by pnpm").unwrap_or("false");
     let package_root = value(parsed, "managed package root").unwrap_or("not set");
     out.push(HumanDetail::Row {
         label: "managed by".to_string(),
         value: format!(
-            "npm: {} · bun: {} · package root {}",
+            "npm: {} · bun: {} · pnpm: {} · package root {}",
             yes_no(managed_by_npm),
             yes_no(managed_by_bun),
+            yes_no(managed_by_pnpm),
             if is_falsy(package_root) {
                 "—".to_string()
             } else {
@@ -263,6 +265,7 @@ fn install_details(parsed: &[ParsedDetail], options: HumanOutputOptions) -> Vec<
             "install context",
             "managed by npm",
             "managed by bun",
+            "managed by pnpm",
             "managed package root",
             "PATH codex entries",
         ],

codex-rs/cli/src/doctor/runtime.rs

@@ -121,6 +121,7 @@ fn install_method_name(context: &InstallContext) -> &'static str {
         InstallMethod::Standalone { .. } => "standalone",
         InstallMethod::Npm => "npm",
         InstallMethod::Bun => "bun",
+        InstallMethod::Pnpm => "pnpm",
         InstallMethod::Brew => "brew",
         InstallMethod::Other => "local build",
     }

codex-rs/cli/src/doctor/snapshots/codex__doctor__output__tests__doctor_human_report_environment_rows.snap

@@ -21,7 +21,7 @@ Environment
       LESS                     -FRX
   ✓ runtime      running local build on darwin-arm64
   ✓ install      consistent
-      managed by               npm: no · bun: no · package root —
+      managed by               npm: no · bun: no · pnpm: no · package root —
   ✓ search       search is OK (bundled)
   ✓ git          git version 2.54.0
       selected git             /usr/bin/git

codex-rs/cli/src/doctor/updates.rs

@@ -133,6 +133,7 @@ fn update_action_label(context: &InstallContext) -> &'static str {
     match &context.method {
         InstallMethod::Npm => "npm install -g @openai/codex",
         InstallMethod::Bun => "bun install -g @openai/codex",
+        InstallMethod::Pnpm => "pnpm add -g @openai/codex",
         InstallMethod::Brew => "brew upgrade --cask codex",
         InstallMethod::Standalone { .. } => "standalone installer",
         InstallMethod::Other => "manual or unknown",
@@ -144,6 +145,7 @@ fn fetch_latest_version(context: &InstallContext) -> Result<String, String> {
         InstallMethod::Brew => fetch_homebrew_cask_version(),
         InstallMethod::Npm
         | InstallMethod::Bun
+        | InstallMethod::Pnpm
         | InstallMethod::Standalone { .. }
         | InstallMethod::Other => fetch_latest_github_release_version(),
     }
@@ -223,6 +225,13 @@ mod tests {
             }),
             "npm install -g @openai/codex"
         );
+        assert_eq!(
+            update_action_label(&InstallContext {
+                method: InstallMethod::Pnpm,
+                package_layout: None,
+            }),
+            "pnpm add -g @openai/codex"
+        );
         assert_eq!(
             update_action_label(&InstallContext {
                 method: InstallMethod::Other,