feat: add agent fallback and preemptive-compaction restoration

- Add agent visibility fallback for first-run scenarios
- Restore preemptive-compaction hook
- Update migration and schema for preemptive-compaction restoration

src/hooks/index.ts

@@ -36,3 +36,4 @@ export { createSubagentQuestionBlockerHook } from "./subagent-question-blocker";
 export { createStopContinuationGuardHook, type StopContinuationGuard } from "./stop-continuation-guard";
 export { createCompactionContextInjector, type SummarizeContext } from "./compaction-context-injector";
 export { createUnstableAgentBabysitterHook } from "./unstable-agent-babysitter";
+export { createPreemptiveCompactionHook } from "./preemptive-compaction";