## Why
Resuming a thread without an explicit `cwd` should restore that thread's latest
retained setting. Forked history can contain settings copied from another
thread, while compaction can move the latest setting outside the replay window.
## What changed
- Record the owning thread ID on new settings snapshots and only use snapshots
owned by the resumed thread when restoring `cwd`. Older snapshots without an
owner remain readable but do not override the startup `cwd`.
- Checkpoint the current settings after compaction and serialize checkpoints
with settings updates so the retained history contains an accepted, current
snapshot.
- Cover resume behavior across compaction, forks, reverts, legacy histories,
and concurrent settings updates.
GitOrigin-RevId: 1efc9cf55472d6b88c465c4efe44672a232dbf64