test(FN-4809): complete Step 2 — cover merge attempt audit emission

Fusion-Task-Id: FN-4809
Fusion-Task-Lineage: bd632e33-b376-47de-ad99-da4610ae4690

packages/engine/src/__tests__/merger-merge-attempt-audit.test.ts

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+import { describe, expect, it, vi } from "vitest";
+import { createRunAuditor } from "../run-audit.js";
+import { emitMergeAttemptAuditEvent } from "../merger.js";
+import type { RunAuditEventInput, TaskStore } from "@fusion/core";
+
+describe("merge attempt run_audit emission (FN-4809)", () => {
+  it("emits git merge:start with merge-attempt phase consumed by reliability metric", async () => {
+    const recordRunAuditEvent = vi.fn(async (_input: RunAuditEventInput) => {});
+    const store = {
+      recordRunAuditEvent,
+    } as unknown as TaskStore;
+
+    const audit = createRunAuditor(store, {
+      runId: "run-4809",
+      agentId: "agent-4809",
+      taskId: "FN-4809",
+      phase: "merge",
+    });
+
+    await emitMergeAttemptAuditEvent({
+      audit,
+      branch: "fusion/FN-4809",
+      attemptNum: 1,
+      mergeConflictStrategy: "smart-prefer-main",
+      attemptLabel: "Attempt 1: AI merge",
+      taskId: "FN-4809",
+    });
+
+    expect(recordRunAuditEvent).toHaveBeenCalledTimes(1);
+    const event = recordRunAuditEvent.mock.calls[0][0];
+    expect(event.domain).toBe("git");
+    expect(event.mutationType).toBe("merge:start");
+    expect(event.taskId).toBe("FN-4809");
+    expect(event.metadata?.phase).toBe("merge-attempt-1");
+    expect(event.metadata?.phase).toMatch(/^merge-attempt-/);
+  });
+
+  it("swallows audit-store failures so merge attempts are not blocked", async () => {
+    const store = {
+      recordRunAuditEvent: vi.fn(async () => {
+        throw new Error("db unavailable");
+      }),
+    } as unknown as TaskStore;
+
+    const audit = createRunAuditor(store, {
+      runId: "run-4809-err",
+      agentId: "agent-4809",
+      taskId: "FN-4809",
+      phase: "merge",
+    });
+
+    await expect(
+      emitMergeAttemptAuditEvent({
+        audit,
+        branch: "fusion/FN-4809",
+        attemptNum: 2,
+        mergeConflictStrategy: "smart-prefer-main",
+        attemptLabel: "Attempt 2",
+        taskId: "FN-4809",
+      }),
+    ).resolves.toBeUndefined();
+  });
+});