Add worktree session creation to the agents overview (#45276)

## What changed

- Add a configurable `new_worktree` action, bound to `w`, for local sessions with worktree support enabled.
- Create the worktree from the cached project default branch, preferring remote `HEAD` and falling back to conventional `main` or `master` refs without fetching. Preserve the selected subdirectory and source checkout edits.
- Start and bind a blank session in the new worktree, preserving the selected approval reviewer without sending an initial turn.
- Show creation progress, pause conflicting actions, clean up unclaimed clean worktrees, and report retained checkout paths when session startup fails. Clear pending creation state on reconnect.

## Testing

Add coverage for default-branch selection, source checkout preservation, session ownership and approval settings, cleanup, startup failures, reconnect state, and busy-state rendering. Extend Git environment isolation coverage and test unrelated non-UTF-8 refs.

GitOrigin-RevId: 771ddc12d04dbf0d12e77e9c96c8386cf31e67c5

codex-rs/worktree/src/git.rs

@@ -94,6 +94,51 @@ pub(crate) fn git_path_from_bytes(bytes: &[u8]) -> Result<PathBuf> {
     }
 }
 
+/// Resolves the cached repository default without fetching or inheriting Git selectors.
+/// Prefer a remote HEAD (origin first), then conventional main/master refs.
+pub fn default_worktree_base(cwd: &Path) -> Result<String> {
+    let output = git_output(
+        cwd,
+        GitOperation::Metadata,
+        [
+            "for-each-ref",
+            "--format=%(refname) %(symref)",
+            "refs/remotes",
+            "refs/heads",
+        ],
+    )?;
+    // Unrelated refs may contain non-UTF-8 bytes. Decode only the chosen base,
+    // because CreateWorktree accepts a UTF-8 revision.
+    let branches = output
+        .stdout
+        .split(|byte| *byte == b'\n')
+        .filter_map(|line| {
+            let line = line.strip_suffix(b"\r").unwrap_or(line);
+            let separator = line.iter().position(|byte| *byte == b' ')?;
+            Some((&line[..separator], &line[separator + 1..]))
+        })
+        .collect::<Vec<_>>();
+    let base = branches
+        .iter()
+        .filter(|(name, target)| name.ends_with(b"/HEAD") && !target.is_empty())
+        .min_by_key(|(name, _)| (!name.starts_with(b"refs/remotes/origin/"), *name))
+        .map(|(_, target)| *target)
+        .or_else(|| {
+            [
+                b"refs/remotes/origin/main".as_slice(),
+                b"refs/remotes/origin/master".as_slice(),
+                b"refs/heads/main".as_slice(),
+                b"refs/heads/master".as_slice(),
+            ]
+            .into_iter()
+            .find(|candidate| branches.iter().any(|(branch, _)| branch == candidate))
+        })
+        .context("Could not determine the project's default branch.")?;
+    std::str::from_utf8(base)
+        .context("The project's default branch is not valid UTF-8.")
+        .map(str::to_owned)
+}
+
 fn base_git_command(cwd: &Path) -> Command {
     let mut command = Command::new("git");
     // Git wrappers export repository-local state to their children. Select this

codex-rs/worktree/src/git_tests.rs

@@ -166,3 +166,33 @@ fn write_marker_script(path: &Path, marker: &Path) -> Result<()> {
     fs::set_permissions(path, fs::Permissions::from_mode(0o755))?;
     Ok(())
 }
+
+#[cfg(unix)]
+#[test]
+fn default_base_ignores_unrelated_non_utf8_refs() -> Result<()> {
+    let (_directory, root) = repository()?;
+    let head = git_stdout(&root, ["rev-parse", "HEAD"])?;
+    // Packed refs work even on filesystems that cannot store non-UTF-8 filenames.
+    fs::write(
+        root.join(".git/packed-refs"),
+        [head.as_bytes(), b" refs/heads/unrelated-\xff\n"].concat(),
+    )?;
+    assert_eq!(super::default_worktree_base(&root)?, "refs/heads/main");
+    setup_git(
+        &root,
+        &["update-ref", "refs/remotes/origin/release/stable", "HEAD"],
+    )?;
+    setup_git(
+        &root,
+        &[
+            "symbolic-ref",
+            "refs/remotes/origin/HEAD",
+            "refs/remotes/origin/release/stable",
+        ],
+    )?;
+    assert_eq!(
+        super::default_worktree_base(&root)?,
+        "refs/remotes/origin/release/stable"
+    );
+    Ok(())
+}

codex-rs/worktree/src/lib.rs

@@ -20,6 +20,7 @@ use std::path::Component;
 use std::path::Path;
 use std::path::PathBuf;
 
+pub use git::default_worktree_base;
 pub use settings::DEFAULT_WORKTREE_KEEP_COUNT;
 pub use settings::WorktreeSettings;