## 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
## Why
Post-commit work can overlap with another settings write. Reading the session
again afterward could make a settings operation report or use the later state
instead of the state that it committed.
## What changed
- Return the committed configuration and `ThreadSettingsSnapshot` from session
settings updates.
- Use that commit result when creating a turn and emitting
`ThreadSettingsApplied`, while retaining current-state snapshots for
synthesized fork history.
- Route turn-start updates through the shared settings update path.
## Testing
Add coverage for standalone and turn-start updates that pause after committing,
restore different settings concurrently, and verify that each operation keeps
its original configuration and notification snapshot.
GitOrigin-RevId: cee5be9536d2840170893e6eb0c64cd039fb0a96
rhan-oai