* fix(native-chat): add reconciliation to catch missed transcript updates
Periodic reconciliation catches file changes that fs.watch may miss on
remote filesystems. Event-driven drains use a bounded max-wait timer to
ensure responsiveness. Extracts timer logic into a scheduler module for
testability and maintainability.
* fix(native-chat): add reconciliation to catch missed transcript updates
Detects same-size file rewrites and native watcher failures by reconciling
transcript state even when fs.watch events don't fire. Extracts watcher
binding into a dedicated module that gracefully degrades to
reconciliation-only mode when native watch is unavailable. Adds test
coverage for watcher rebind failures, parent-directory replacements, and
unsubscribe races.
* Document transcript watcher reconciliation contract
Clarify that bind() is best-effort with reconciliation fallback,
invalidate() detaches from stale identities, and the caller's polling
loop owns transcript liveness. Supports resilience on remote filesystems.
