Extract handleWorkerMessage (380 lines, 12 positional args) into dispatcher
+ focused handler modules. Dispatcher now routes by message.type to
run-log / run-status / run-finished handlers, each receiving (event, deps,
context) triple. run-finished is further decomposed into 5 steps:
finalizeRun, accumulateAndRotateSession, emitAndNotifyCompletion,
runPostCompletionAutomation, triggerSelfWake.
No behavior change: all branches, notifications, lease renewals, circuit
breaker, and escalation semantics preserved. Schema validation stays at
dispatcher top level.
ZacharyZhang-NY
cc02b45864