refactor(worker): split god-handler into per-message type files

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.

src/main/worker/handlers/run-finished-handler.ts

@@ -0,0 +1,22 @@
+import {
+  accumulateAndRotateSession,
+  emitAndNotifyCompletion,
+  finalizeRun,
+  runPostCompletionAutomation,
+  triggerSelfWake,
+} from "./run-finished-helpers";
+import type { HandlerContext, HandlerDeps, WorkerMessageEvent } from "./handler-context";
+
+export function handleRunFinished(
+  event: Extract<WorkerMessageEvent, { type: "run-finished" }>,
+  deps: HandlerDeps,
+  context: HandlerContext,
+): void {
+  const rfCtx = finalizeRun(event, deps, context);
+  if (!rfCtx) return;
+
+  accumulateAndRotateSession(event, deps, rfCtx);
+  emitAndNotifyCompletion(event, deps, rfCtx);
+  const { hadDeferredWakes } = runPostCompletionAutomation(event, deps, context, rfCtx);
+  triggerSelfWake(event, deps, context, rfCtx, hadDeferredWakes);
+}