feat(FN-5438): add manual merge blocker bypass mode for queued tasks

Adds a manual merge blocker mode (FN-5438) that prevents automatic merging and provides a bypass mechanism to resume, wired through the merger, project engine, and task workflow API routes. Includes tests across core, engine route registration, and project engine layers, plus a changeset and documen

Fusion-Task-Id: FN-5438

packages/dashboard/src/routes/__tests__/register-task-workflow-routes.merge.test.ts

@@ -0,0 +1,34 @@
+// @vitest-environment node
+
+import { describe, expect, it, vi } from "vitest";
+import express from "express";
+import type { TaskStore } from "@fusion/core";
+import { createApiRoutes } from "../../routes.js";
+import { request as REQUEST } from "../../test-request.js";
+
+describe("task workflow merge route", () => {
+  it("invokes engine.onMerge for manual merge requests", async () => {
+    const store: TaskStore = {
+      getRootDir: vi.fn(() => process.cwd()),
+      mergeTask: vi.fn(),
+    } as unknown as TaskStore;
+
+    const onMerge = vi.fn(async (id: string) => ({
+      task: { id, column: "done" },
+      branch: `fusion/${id.toLowerCase()}`,
+      merged: true,
+      worktreeRemoved: false,
+      branchDeleted: false,
+    }));
+
+    const app = express();
+    app.use(express.json());
+    app.use("/api", createApiRoutes(store, { onMerge }));
+
+    const res = await REQUEST(app, "POST", "/api/tasks/FN-5438/merge");
+
+    expect(res.status).toBe(200);
+    expect(onMerge).toHaveBeenCalledWith("FN-5438");
+    expect((res.body as { merged: boolean }).merged).toBe(true);
+  });
+});

packages/dashboard/src/routes/register-task-workflow-routes.ts

@@ -997,7 +997,10 @@ export function registerTaskWorkflowRoutes(ctx: ApiRoutesContext, deps: TaskWork
     try {
       const { store: scopedStore, engine } = await getProjectContext(req);
       const merge = engine
-        ? (id: string) => engine.onMerge(id)
+        ? (id: string) => {
+          // Manual merge: bypasses scheduler-transient status blockers (FN-5438). Hard guards still apply.
+          return engine.onMerge(id);
+        }
         : options?.onMerge ?? ((id: string) => scopedStore.mergeTask(id));
       const result = await merge(req.params.id);
       res.json(result);