feat(KB-161): terminate active agent sessions on engine pause

- Add enginePaused agent termination to executor (kills sessions, moves tasks back to todo)
- Add enginePaused agent termination to triage processor (kills sessions, clears specifying status)
- Update enginePaused JSDoc to reflect new termination behavior vs old graceful drain
- Add unit tests for executor/triage pause termination and integration tests for restart flow
- Include changeset for engine pause behavior change

packages/engine/src/executor.ts

@@ -172,7 +172,7 @@ export class TaskExecutor {
    * Listens for `task:moved` to auto-execute tasks moved to `in-progress`,
    * `task:updated` to terminate agent sessions when individual tasks are paused,
    * and `settings:updated` to terminate **all** active agent sessions when
-   * `globalPause` transitions from `false` to `true` (emergency stop).
+   * `globalPause` or `enginePaused` transitions from `false` to `true`.
    * Paused tasks are moved back to `todo` rather than marked as `failed`.
    */
   constructor(
@@ -208,6 +208,18 @@ export class TaskExecutor {
         }
       }
     });
+
+    // When enginePaused transitions from false → true, terminate all active agent sessions.
+    // Same pattern as globalPause: agents are killed, tasks moved to todo (not failed).
+    store.on("settings:updated", ({ settings, previous }) => {
+      if (settings.enginePaused && !previous.enginePaused) {
+        for (const [taskId, session] of this.activeSessions) {
+          executorLog.log(`Engine pause — terminating agent session for ${taskId}`);
+          this.pausedAborted.add(taskId);
+          session.dispose();
+        }
+      }
+    });
   }
 
   /**