`cwd` and `branch` no longer persist to local session-store.db since ~1.0.13

### Describe the bug

Since approximately version 1.0.13 (March 29), the `cwd` and `branch` columns in the local `~/.copilot/session-store.db` `sessions` table are NULL for the majority of new sessions. The data is correctly captured in `workspace.yaml` files under `~/.copilot/session-state/{session-id}/`, but it is not being written to the SQLite database.

### Evidence

Daily NULL rate for `cwd` in the `sessions` table:

| Date | Sessions | NULL cwd | Rate | Notes |
|------|----------|----------|------|-------|
| Mar 25–28 | 40 | 0 | **0%** | Healthy baseline |
| **Mar 29** | **22** | **17** | **77%** | Sharp inflection — 17 zero-turn "ghost" sessions at 19:37 UTC (auto-update restart signature) |
| Mar 30–31 | 22 | 11 | 50% | Intermittent — some sessions still populated correctly |
| Apr 2–3 | 25 | 22 | 88% | Stabilized high |
| Apr 5–12 | 77 | 71 | **92%** | Consistently broken through current (1.0.24) |

`branch` follows the same curve. `summary`, `turns`, `session_files`, and other tables **appear unaffected** based on spot-checking — only `cwd` and `branch` in the `sessions` table show the regression pattern.

### Root cause hypothesis

The [1.0.13-2 changelog](https://github.com/github/copilot-cli/blob/main/changelog.md) (released as a pre-release around March 29–30) includes:

> *"Reduce CLI startup time by running terminal detection, auth, and **git operations in parallel**"*

If the session row is inserted into SQLite before the async git discovery completes, `cwd` and `branch` would be NULL in the database. The `workspace.yaml` files (written by a different code path or updated after git discovery) correctly contain:

```yaml
cwd: C:\Users\\source\
git_root: C:\Users\\source\
branch: master
```

This is consistent with a race condition introduced by the parallelization.

### Verification that this is not self-inflicted

- No custom scripts or tools write to `session-store.db` — all local tooling is read-only (verified via code audit)
- SQLite WAL is healthy — checkpoint succeeded, no lock contention
- No external processes (OneDrive sync, antivirus) touch the `.copilot` directory
- The `sessionSync` config change to `"local"` (April 10) did not cause a second regression — `cwd` was already broken by then

### Steps to reproduce

1. Install Copilot CLI 1.0.13 or later
2. Start several sessions in a git repository over the course of normal use
3. Query the local session store:
```python
import sqlite3
from pathlib import Path
conn = sqlite3.connect(str(Path.home() / '.copilot' / 'session-store.db'))
for r in conn.execute("SELECT id, cwd, branch FROM sessions ORDER BY created_at DESC LIMIT 20").fetchall():
print(r)
```
4. Observe that the majority of sessions have NULL `cwd` and `branch` (in my case, ~78–92% since March 29)
5. For a NULL session, check the corresponding `workspace.yaml`:
```
cat ~/.copilot/session-state/{session-id}/workspace.yaml
```
6. Observe `cwd` and `branch` are correctly populated there

### Impact

- **Local session queries are broken.** Any tooling querying `session-store.db` for sessions by working directory or repository gets incomplete results. ~78% of sessions since March 29 are affected (125+ sessions in my case).
- **Session resume grouping.** The 1.0.18 changelog notes "Session resume picker correctly groups sessions by branch and repository" — this likely can't work correctly when the underlying data is NULL.
- **Third-party tooling.** Users who build automation on top of `session-store.db` (workstream tracking, session digests, stale work detection) lose the ability to filter or classify sessions by repository.

### Recovery

A backfill is possible since `workspace.yaml` has the correct data. A script could read each `~/.copilot/session-state/{id}/workspace.yaml` and UPDATE the corresponding `sessions` row in SQLite.

### Environment

- Copilot CLI: 1.0.24 (regression started in 1.0.13-x timeframe)
- OS: Windows 11
- Local session-store.db: 614 sessions, 125 with NULL `cwd` (all post-March 29)
- `workspace.yaml` files: correctly populated for all sampled NULL-cwd sessions

### Additional note: `repository` column

Separately from this regression, the `repository` column in the `sessions` table has been ~83% NULL for the entire history of the local DB — including the healthy pre-March 29 period. This may be by design (perhaps only populated in the cloud session store), but if it's intended to hold the git remote URL, it appears to have never worked locally. Mentioning in case it's related to the same code path.