Tail appended transcript JSONL instead of rebuilding rendered history on every poll, collapse compacted history for live chat rendering, and replace synchronous session rewrites so tailers detect historical changes.
Fixes#3258
- Migrated test mocking from bun:test mock API to vitest spyOn pattern across 9 test files.
- Extracted mock setup logic into reusable helper functions with Symbol.dispose cleanup pattern.
- Replaced manual beforeEach/afterEach and try-finally blocks with TypeScript 5.2 using declarations.
- Removed 178 lines of boilerplate mock initialization and restoration code from test suite.
can1357