feat(tui): add PR summary statusline items (#20892)

## Why?

The Codex App already exposes branch and PR context in its
branch-details UI. This brings the same context into the CLI footer as
opt-in statusline items, so users can choose the extra signal without
making the default footer busier.

## What?

Add optional `pull-request-number` and `branch-changes` items to the
configurable TUI status line.

- `pull-request-number` shows the open PR for the current checkout and
renders as a clickable terminal hyperlink when OSC 8 links are
supported.
- `branch-changes` shows committed additions/deletions against the
repository default branch, or `No changes` when the branch has no
committed diff.

<img width="1257" height="261" alt="CleanShot 2026-05-03 at 20 44 15"
src="https://github.com/user-attachments/assets/10b4380b-c3e9-4729-9ee1-3f742068fa47"
/>

## Architecture

This follows the same client/app-server split as the Codex App: the TUI
owns presentation, caching, and optional rendering, while
workspace-sensitive `git` and `gh` discovery runs through app-server.

The new TUI-local `workspace_command` layer sends bounded,
non-interactive `command/exec` requests to the active app-server. That
makes the implementation remote-friendly: the TUI does not decide
whether commands run in an embedded local workspace or a remote
workspace, and it does not bypass app-server sandbox or permission
policy.

The branch summary logic stays internal to `codex-tui` because this PR
only needs TUI statusline behavior. The command boundary is still
isolated behind `WorkspaceCommandExecutor`, so the lookup code can be
lifted or reused later without changing statusline rendering.

## How?

- Add a TUI `WorkspaceCommandExecutor` abstraction backed by app-server
`command/exec`.
- Add branch summary probes for:
  - current branch name,
  - open PR metadata,
  - committed branch diff stats against the default branch.
- Prefer remote-tracking default branch refs for diff stats, avoiding
stale or absent local `main` branches.
- Resolve PRs with `gh pr view` first, then fall back to
commit-associated PR lookup across parent/fork repos.
- Add `/statusline` picker entries, preview values, rendering, and OSC 8
clickable PR links.
- Keep all probes best-effort so missing `git`, missing `gh`, auth
failures, or non-git directories hide optional items instead of
surfacing footer errors.

## Validation

- `cargo test -p codex-tui branch_summary -- --nocapture`
- Snapshot coverage for the `/statusline` preview/setup rendering paths
- Hyperlink rendering coverage for clickable PR statusline cells

codex-rs/tui/src/chatwidget.rs

@@ -349,11 +349,13 @@ use self::status_surfaces::TerminalTitleStatusKind;
 mod user_messages;
 use self::user_messages::PendingSteerCompareKey;
 use self::user_messages::UserMessageDisplay;
+pub(crate) use crate::branch_summary::StatusLineGitSummary;
 use crate::streaming::chunking::AdaptiveChunkingPolicy;
 use crate::streaming::commit_tick::CommitTickScope;
 use crate::streaming::commit_tick::run_commit_tick;
 use crate::streaming::controller::PlanStreamController;
 use crate::streaming::controller::StreamController;
+use crate::workspace_command::WorkspaceCommandRunner;
 
 use chrono::Local;
 use codex_app_server_protocol::AskForApproval;
@@ -554,6 +556,11 @@ pub(crate) struct ChatWidgetInit {
     pub(crate) config: Config,
     pub(crate) frame_requester: FrameRequester,
     pub(crate) app_event_tx: AppEventSender,
+    /// App-server-backed runner used by status surfaces for workspace metadata probes.
+    ///
+    /// Tests that do not exercise git status-line refreshes may leave this unset. Production TUI
+    /// construction provides a runner for the active app-server session.
+    pub(crate) workspace_command_runner: Option<WorkspaceCommandRunner>,
     pub(crate) initial_user_message: Option<UserMessage>,
     pub(crate) enhanced_keys_supported: bool,
     pub(crate) has_chatgpt_account: bool,
@@ -972,6 +979,8 @@ pub(crate) struct ChatWidget {
     current_rollout_path: Option<PathBuf>,
     // Current working directory (if known)
     current_cwd: Option<PathBuf>,
+    // App-server-backed command runner for status-line workspace metadata lookups.
+    workspace_command_runner: Option<WorkspaceCommandRunner>,
     // Instruction source files loaded for the current session, supplied by app-server.
     instruction_source_paths: Vec<AbsolutePathBuf>,
     // Runtime network proxy bind addresses from SessionConfigured.
@@ -1004,6 +1013,14 @@ pub(crate) struct ChatWidget {
     status_line_branch_pending: bool,
     // True once we've attempted a branch lookup for the current CWD.
     status_line_branch_lookup_complete: bool,
+    // Cached PR and branch-change summary for the active status-line cwd.
+    status_line_git_summary: Option<StatusLineGitSummary>,
+    // CWD used to resolve the cached Git summary; change resets summary state.
+    status_line_git_summary_cwd: Option<PathBuf>,
+    // True while an async Git summary lookup is in flight.
+    status_line_git_summary_pending: bool,
+    // True once we've attempted a Git summary lookup for the current CWD.
+    status_line_git_summary_lookup_complete: bool,
     // Current thread-goal status shown in the status line when plan mode is inactive.
     current_goal_status_indicator: Option<GoalStatusIndicator>,
     current_goal_status: Option<GoalStatusState>,
@@ -1831,6 +1848,11 @@ impl ChatWidget {
         self.bottom_pane.set_status_line(status_line);
     }
 
+    /// Sets the terminal hyperlink target for the currently rendered footer status line.
+    pub(crate) fn set_status_line_hyperlink(&mut self, url: Option<String>) {
+        self.bottom_pane.set_status_line_hyperlink(url);
+    }
+
     /// Forwards the contextual active-agent label into the bottom-pane footer pipeline.
     ///
     /// `ChatWidget` stays a pass-through here so `App` remains the owner of "which thread is the
@@ -1929,6 +1951,22 @@ impl ChatWidget {
         self.refresh_status_surfaces();
     }
 
+    /// Stores async Git summary lookup results for the current status-line cwd.
+    pub(crate) fn set_status_line_git_summary(
+        &mut self,
+        cwd: PathBuf,
+        summary: StatusLineGitSummary,
+    ) {
+        if self.status_line_git_summary_cwd.as_ref() != Some(&cwd) {
+            self.status_line_git_summary_pending = false;
+            return;
+        }
+        self.status_line_git_summary = Some(summary);
+        self.status_line_git_summary_pending = false;
+        self.status_line_git_summary_lookup_complete = true;
+        self.refresh_status_surfaces();
+    }
+
     fn collect_runtime_metrics_delta(&mut self) {
         if let Some(delta) = self.session_telemetry.runtime_metrics_summary() {
             self.apply_runtime_metrics_delta(delta);
@@ -2499,6 +2537,7 @@ impl ChatWidget {
             self.needs_final_message_separator = false;
             self.had_work_activity = false;
             self.request_status_line_branch_refresh();
+            self.request_status_line_git_summary_refresh();
         }
         // Mark task stopped and request redraw now that all content is in history.
         self.pending_status_indicator_restore = false;
@@ -2960,6 +2999,7 @@ impl ChatWidget {
         self.plan_stream_controller = None;
         self.pending_status_indicator_restore = false;
         self.request_status_line_branch_refresh();
+        self.request_status_line_git_summary_refresh();
         self.maybe_show_pending_rate_limit_prompt();
     }
 
@@ -4768,6 +4808,7 @@ impl ChatWidget {
             config,
             frame_requester,
             app_event_tx,
+            workspace_command_runner,
             initial_user_message,
             enhanced_keys_supported,
             has_chatgpt_account,
@@ -4960,6 +5001,7 @@ impl ChatWidget {
             feedback,
             current_rollout_path: None,
             current_cwd,
+            workspace_command_runner,
             instruction_source_paths: Vec::new(),
             session_network_proxy: None,
             status_line_invalid_items_warned,
@@ -4973,6 +5015,10 @@ impl ChatWidget {
             status_line_branch_cwd: None,
             status_line_branch_pending: false,
             status_line_branch_lookup_complete: false,
+            status_line_git_summary: None,
+            status_line_git_summary_cwd: None,
+            status_line_git_summary_pending: false,
+            status_line_git_summary_lookup_complete: false,
             current_goal_status_indicator: None,
             current_goal_status: None,
             goal_status_active_turn_started_at: None,