feat(KB-093): add PR-first merge mode with configurable merge strategies

- Add mergeStrategy setting (fast-forward, squash, merge-commit) to config
- Implement PR-first auto-completion flow that monitors PR merge status
- Wire PR monitoring service to detect merge completion and trigger auto-close
- Add PR status UI to dashboard with merge progress indicator
- Update settings modal with merge strategy selector
- Add changeset for PR-first merge mode feature

packages/engine/src/index.ts

@@ -10,4 +10,5 @@ export { WorktreePool, scanIdleWorktrees, cleanupOrphanedWorktrees } from "./wor
 export { createLogger, type Logger } from "./logger.js";
 export { isUsageLimitError, UsageLimitPauser } from "./usage-limit-detector.js";
 export { PrMonitor, type PrComment, type TrackedPr, type OnNewCommentsCallback } from "./pr-monitor.js";
+export { PrCommentHandler } from "./pr-comment-handler.js";
 export { NtfyNotifier, type NtfyNotifierOptions } from "./notifier.js";

packages/engine/src/pr-comment-handler.test.ts

@@ -4,7 +4,7 @@ import type { TaskStore } from "@kb/core";
 
 const mockStore = {
   addSteeringComment: vi.fn(),
-  createTask: vi.fn(),
+  createTask: vi.fn().mockResolvedValue({ id: "KB-123" }),
 } as unknown as TaskStore;
 
 describe("PrCommentHandler", () => {
@@ -176,6 +176,23 @@ describe("PrCommentHandler", () => {
         "agent"
       );
     });
+
+    it("calls out follow-up context when feedback arrives after PR is merged", async () => {
+      await handler.handleNewComments("KB-001", { ...mockPrInfo, status: "merged" }, [
+        {
+          id: 1,
+          body: "Please add one more regression test",
+          user: { login: "reviewer" },
+          created_at: new Date().toISOString(),
+          updated_at: new Date().toISOString(),
+          html_url: "https://github.com/owner/repo/pull/42#issuecomment-1",
+        },
+      ]);
+
+      const text = mockStore.addSteeringComment.mock.calls[0][1] as string;
+      expect(text).toContain("This PR is already merged");
+      expect(text).toContain("follow-up work");
+    });
   });
 
   describe("createFollowUpTask", () => {

packages/engine/src/pr-comment-handler.ts

@@ -128,6 +128,9 @@ export class PrCommentHandler {
 
     lines.push(`**PR Review Feedback** from @${comment.user.login}`);
     lines.push(`**PR:** #${prInfo.number} (${prInfo.status})`);
+    if (prInfo.status !== "open") {
+      lines.push(`**Note:** This PR is already ${prInfo.status}. Treat the feedback as follow-up work.`);
+    }
     lines.push("");
 
     // Truncate comment body if too long

packages/engine/src/pr-monitor.test.ts

@@ -44,6 +44,19 @@ describe("PrMonitor", () => {
     });
   });
 
+  describe("updatePrInfo", () => {
+    it("updates tracked PR metadata without restarting monitoring", () => {
+      monitor.startMonitoring("KB-001", "owner", "repo", mockPrInfo);
+      const updatedPrInfo = { ...mockPrInfo, status: "merged" as const };
+
+      monitor.updatePrInfo("KB-001", updatedPrInfo);
+
+      const tracked = monitor.getTrackedPrs();
+      expect(tracked.get("KB-001")?.prInfo.status).toBe("merged");
+      expect(tracked.get("KB-001")?.owner).toBe("owner");
+    });
+  });
+
   describe("stopMonitoring", () => {
     it("stops monitoring a task", () => {
       monitor.startMonitoring("KB-001", "owner", "repo", mockPrInfo);

packages/engine/src/pr-monitor.ts

@@ -154,6 +154,16 @@ export class PrMonitor {
     prMonitorLog.log(`Started monitoring PR #${prInfo.number} for task ${taskId}`);
   }
 
+  /**
+   * Update the cached PR metadata for an already tracked task.
+   * Keeps comment polling state intact while refreshing fields like PR status.
+   */
+  updatePrInfo(taskId: string, prInfo: PrInfo): void {
+    const tracked = this.trackedPrs.get(taskId);
+    if (!tracked) return;
+    tracked.prInfo = prInfo;
+  }
+
   /**
    * Stop monitoring a PR.
    */

packages/engine/src/scheduler.ts

@@ -150,11 +150,14 @@ export class Scheduler {
 
       // Check if we're already monitoring this task
       const tracked = this.options.prMonitor.getTrackedPrs();
-      if (!tracked.has(task.id)) {
-        const repo = getCurrentGitHubRepo(this.store.getRootDir());
-        if (repo) {
-          this.options.prMonitor.startMonitoring(task.id, repo.owner, repo.repo, task.prInfo);
-        }
+      if (tracked.has(task.id)) {
+        this.options.prMonitor.updatePrInfo(task.id, task.prInfo);
+        return;
+      }
+
+      const repo = getCurrentGitHubRepo(this.store.getRootDir());
+      if (repo) {
+        this.options.prMonitor.startMonitoring(task.id, repo.owner, repo.repo, task.prInfo);
       }
     });
   }