feat(KB-633): add Mission REST API routes for real-time steering

- Create mission-routes.ts with comprehensive REST API for task steering
- Add GET/PUT /api/tasks/:id/mission endpoints for mission state management
- Add POST endpoints for steering comments, pause/unpause, retry, and cancel
- Mount mission routes in dashboard API server
- Update core store with mission-related functionality
- Refactor executor: remove old mission logic, update tests

packages/core/src/store.ts

@@ -8,6 +8,7 @@ import { VALID_TRANSITIONS, DEFAULT_SETTINGS, DEFAULT_GLOBAL_SETTINGS, DEFAULT_P
 import { GlobalSettingsStore } from "./global-settings.js";
 import { Database, toJson, toJsonNullable, fromJson } from "./db.js";
 import { detectLegacyData, migrateFromLegacy } from "./db-migrate.js";
+import { MissionStore } from "./mission-store.js";
 
 export interface TaskStoreEvents {
   "task:created": [task: Task];
@@ -54,6 +55,8 @@ export class TaskStore extends EventEmitter<TaskStoreEvents> {
   private pollInterval: ReturnType<typeof setInterval> | null = null;
   /** Last known modification timestamp for change detection */
   private lastKnownModified: number = 0;
+  /** Cached MissionStore instance */
+  private missionStore: MissionStore | null = null;
 
   constructor(private rootDir: string, globalSettingsDir?: string) {
     super();
@@ -2659,4 +2662,15 @@ ${notificationsSection}`;
     this.db.prepare("DELETE FROM activityLog").run();
     this.db.bumpLastModified();
   }
+
+  /**
+   * Get the MissionStore instance for mission hierarchy operations.
+   * Lazily initializes the MissionStore on first access.
+   */
+  getMissionStore(): MissionStore {
+    if (!this.missionStore) {
+      this.missionStore = new MissionStore(this.kbDir, this.db);
+    }
+    return this.missionStore;
+  }
 }

packages/dashboard/src/routes.ts

@@ -20,6 +20,7 @@ import {
   hasIssueBadgeFieldsChanged,
   type BadgeUrlComponents,
 } from "./github-webhooks.js";
+import { createMissionRouter } from "./mission-routes.js";
 
 /**
  * Minimal interface matching pi-coding-agent's ModelRegistry API surface
@@ -5664,6 +5665,10 @@ Output ONLY the prompt text (no markdown, no explanations).`;
     }
   });
 
+  // ── Mission Routes ─────────────────────────────────────────────────────────
+  // Mount mission routes at /api/missions
+  router.use("/missions", createMissionRouter(store));
+
   return router;
 }