Add working-directory commands to the TUI (#38894)

## What changed

- Add `/cd [path]` for changing an idle local session's working directory while preserving conversation history. Relative paths resolve from the current directory, and omitting the path selects `~`.
- Reload project configuration, instructions, permissions, keybindings, file search, and hooks for the destination before replacing the active session.
- Reject unsafe transitions, including active or queued work, background terminals, remote environments, untrusted destinations, and incompatible permission profiles.
- Add `/pwd` and its `/cwd` alias to display the current working directory, and discard asynchronous results left over from the previous directory.

## Testing

- Cover command parsing, aliases, default paths, session eligibility, transition failures, history preservation, destination policy loading, hooks, and stale events.

GitOrigin-RevId: 1a987c029f157a087ba02c0f26e022260409132b

codex-rs/tui/src/app_event.rs

@@ -263,6 +263,7 @@ pub(crate) enum AppEvent {
     SyncThreadGitBranch {
         thread_id: ThreadId,
         branch: String,
+        cwd: PathBuf,
     },
 
     /// Fetch a persistent cross-session message history entry by offset.
@@ -284,6 +285,12 @@ pub(crate) enum AppEvent {
         name: Option<String>,
     },
 
+    /// Change the working directory of the originating idle primary thread.
+    ChangeWorkingDirectory {
+        thread_id: ThreadId,
+        requested_cwd: PathBuf,
+    },
+
     /// Result of the fresh startup thread that is attached after the input UI is live.
     StartupThreadStarted {
         result: Result<AppServerStartedThread, String>,
@@ -504,7 +511,7 @@ pub(crate) enum AppEvent {
     },
 
     /// Result of computing a `/diff` command.
-    DiffResult(String),
+    DiffResult(PathBuf, String),
 
     /// Open the app link view in the bottom pane.
     OpenAppLink {
@@ -748,6 +755,7 @@ pub(crate) enum AppEvent {
 
     /// Result of refreshing plugin mention bindings.
     PluginMentionsLoaded {
+        cwd: PathBuf,
         plugins: Option<Vec<PluginCapabilitySummary>>,
     },
 
@@ -778,6 +786,7 @@ pub(crate) enum AppEvent {
     /// command path because those callers expect the visible skill state to be current when their command
     /// completes.
     SkillsListLoaded {
+        cwd: PathBuf,
         result: Result<SkillsListResponse, String>,
     },