[Bugs] Title: Restoring an archived worktree session leaves it anchored to a stale, ...

**Mood:** 😔
**Category:** Bugs

Title: Restoring an archived worktree session leaves it anchored to a stale, empty folder (breaks file tools + custom-agent discovery)

Affected version: 1.0.66-1 (desktop app, Windows)

## Describe the bug
After restoring a worktree-backed session from archive, the session's working directory still points at the *original* generated worktree folder, but the actual git worktree has been re-created under a different (branch-named) folder. The original folder is left as an empty, non-git stub, so the session is anchored to a dead directory.

## Steps to reproduce
1. Create a worktree-backed session (generates a folder, e.g. `/`).
2. Rename the branch early in the session (folder and branch names now diverge).
3. Archive the session, then later restore it from archive.
4. `git worktree list` shows the worktree at `/`, but the session's working directory is still `/` — now empty (no `.git`, no repo content, no `.github/agents/`).

## Impact
- File/edit/glob tools default to the dead path and fail until absolute paths to the real worktree are used.
- Custom agents are discovered from `/.github/agents/`; because cwd is the empty stub, all custom agents vanish from in-session tooling (only built-in agents remain) — even though the app UI still lists them.
- Shell commands default to the wrong directory.

## Expected behavior
On restore, the session's working directory should be updated to the worktree's current path (or the worktree restored at the path the session references), so file tools and `.github/agents/` discovery keep working.

## Workaround
Restart/reopen the session to re-anchor cwd; until then, pass absolute paths to the real worktree.

## Possibly related
- #3931 (worktree/cwd divergence affecting resume)
- #3528 (agent starts in wrong cwd)

---
| Field | Value |
| --- | --- |
| App version | 1.0.12 |
| OS | Windows 10.0.26200 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 3 |

Start by tracing the archive-restore flow and how it resolves the session working directory against the recreated Git worktree. Reproduce the branch-rename and restore sequence on Windows, then verify that the session cwd points to the real worktree and that file tools, shell commands, and .github/agents/ discovery work without absolute paths.

索引モデルが issue の本文から書いたものです。