fix(pi): return full executedWorkThisPass for synthetic-todo gate

Expose runPipeline's existing executedWorkThisPass signal and use it for synthetic todowrite cache-bust gating. Pending-op-only and reasoning-clearing execute passes now get the same cache-bust synthetic injection window as heuristic cleanup passes.\n\nVerification: bun test packages/pi-plugin/src/context-handler.test.ts