Pivot out of agent worktree before prune in branch-finish (#423)

When `gx branch finish --cleanup` is invoked from inside the agent
worktree being cleaned up, the later `gx worktree prune` subprocess
inherits `cwd=repo_root` from the CLI, so its own active-cwd check
can't see that the calling shell is still sitting in the worktree
about to be deleted. The prune then removes the directory, the next
subprocess spawn fails with `ENOENT uv_cwd`, and `set -e` flips the
script exit code to 1 even though the merge and push already
succeeded.

Pivot the shell to `repo_root` right before prune when the caller's
cwd equals the source worktree, so the worktree can be removed
without invalidating the caller's cwd. Also guard the trailing
"still exists because it is the active shell cwd" message behind an
on-disk `-d "$source_worktree"` check so we only print the
leave-directory reminder when the worktree really is still there.

Co-authored-by: NagyVikt <nagy.viktordp@gmail.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 3 people

scripts/agent-branch-finish.sh

@@ -830,13 +830,24 @@ if [[ "$CLEANUP_AFTER_MERGE" -eq 1 ]]; then
   if [[ "$DELETE_REMOTE_BRANCH" -eq 1 ]]; then
     prune_args+=(--delete-remote-branches)
   fi
+
+  # Pivot out of the agent worktree before the prune may remove it. The prune
+  # subprocess inherits cwd=repo_root from the CLI caller, so its own active
+  # cwd check can't see that our shell is sitting in the worktree it is about
+  # to delete. Without this pivot the directory disappears mid-call, every
+  # subsequent subprocess spawn fails with ENOENT uv_cwd, and `set -e` flips
+  # the script exit code to 1 even though the merge succeeded.
+  if [[ "$current_worktree" == "$source_worktree" && "$source_worktree" == "${agent_worktree_root}"/* ]]; then
+    cd "$repo_root" 2>/dev/null || true
+  fi
+
   if ! run_guardex_cli worktree prune "${prune_args[@]}"; then
     echo "[agent-branch-finish] Warning: automatic worktree prune failed." >&2
     echo "[agent-branch-finish] You can run manual cleanup: gx cleanup --base ${BASE_BRANCH}" >&2
   fi
 
   echo "[agent-branch-finish] Merged '${SOURCE_BRANCH}' into '${BASE_BRANCH}' via ${merge_status} flow and cleaned source branch/worktree."
-  if [[ "$source_worktree" == "$current_worktree" && "$source_worktree" == "${agent_worktree_root}"/* ]]; then
+  if [[ "$source_worktree" == "$current_worktree" && "$source_worktree" == "${agent_worktree_root}"/* && -d "$source_worktree" ]]; then
     echo "[agent-branch-finish] Current worktree '${source_worktree}' still exists because it is the active shell cwd." >&2
     echo "[agent-branch-finish] Leave this directory, then run: gx cleanup --base ${BASE_BRANCH}" >&2
   fi