Add characterization tests first, then split the hot spots into small helpers:
- STT/TTS settings updates move to extensions/piagentui-speech-settings.ts (rule tables)
- defaultExtractData is split into diff/diagnostic/output extractors
- getToolSummaryCategory becomes an ordered rule table (toolSummary.ts)
- sanitizePersistedTerminalLayoutMap is split per level
- duplicated diff stats helpers are merged into utils/diffStats.ts