Drop cleanup.ts, session-created-handler.ts, and session-deleted-handler.ts which were never wired up; the lifecycle logic they contained lives inline in TmuxSessionManager. Barrels trimmed to match.
Extract session lifecycle, polling, grid planning, and event handling: - polling.ts: session polling controller with stability detection - event-handlers.ts: session created/deleted handlers - grid-planning.ts, spawn-action-decider.ts, spawn-target-finder.ts - session-status-parser.ts, session-message-count.ts - cleanup.ts, polling-constants.ts, tmux-grid-constants.ts
YeonGyu-Kim