feat(engine): effective column agent becomes the execution principal

U5: action-gating contexts, the heartbeat deferral gate, a two-pass
resumeTaskForAgent, and the reverse-direction agent.taskId guards (via a
new isAgentEffectivelyExecuting callback wired at the in-process runtime)
all consult the column-effective agent; the restart watcher re-resolves
column bindings per tick for bound graph sessions, hot-swapping on
agent-changed and falling back without restart on agent-deleted.

packages/cli/src/commands/dashboard.ts

@@ -1974,6 +1974,11 @@ export async function runDashboard(port: number, opts: { paused?: boolean; dev?:
           });
         },
         store,
+        // Dev-mode scheduler: no TaskExecutor runs here (engine not started), so
+        // neither `isTaskExecuting` nor the U5 reverse-direction
+        // `isAgentEffectivelyExecuting` guard has a source — both stay unwired (the
+        // guards simply never fire), matching the prior `isTaskExecuting` omission.
+        // The real wiring is the InProcessRuntime construction site.
       );
       triggerScheduler.start();