test(FN-4383): complete Step 2 — add base commit capture unit tests

Fusion-Task-Id: FN-4383
Fusion-Task-Lineage: 69516bdf-34d1-405c-8bc9-b558c4780863

packages/engine/src/__tests__/executor-base-commit-capture.test.ts

@@ -0,0 +1,96 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import "./executor-test-helpers.js";
+import { TaskExecutor } from "../executor.js";
+import { executorLog } from "../logger.js";
+import type { Task } from "@fusion/core";
+import { createMockStore, mockedExec, mockedExecSync, resetExecutorMocks } from "./executor-test-helpers.js";
+
+function makeTask(overrides: Partial<Task> = {}): Task {
+  return {
+    id: "FN-4383",
+    title: "Test",
+    description: "Test",
+    column: "in-progress",
+    dependencies: [],
+    steps: [],
+    currentStep: 0,
+    log: [],
+    createdAt: new Date().toISOString(),
+    updatedAt: new Date().toISOString(),
+    ...overrides,
+  } as Task;
+}
+
+describe("captureBaseCommitSha", () => {
+  beforeEach(() => {
+    resetExecutorMocks();
+  });
+
+  it("captures merge-base for fresh worktree", async () => {
+    mockedExec.mockImplementation((cmd: any, _opts: any, cb: any) => cb(null, cmd.includes("merge-base") ? "abc1234\n" : ""));
+    const store = createMockStore();
+    const executor = new TaskExecutor(store, "/tmp/test");
+    const audit = { git: vi.fn().mockResolvedValue(undefined) };
+
+    await (executor as any).captureBaseCommitSha(makeTask(), "/tmp/test/.worktrees/fn-4383", audit);
+
+    expect(store.updateTask).toHaveBeenCalledWith("FN-4383", { baseCommitSha: "abc1234" });
+    expect(audit.git).toHaveBeenCalledWith(expect.objectContaining({ metadata: { purpose: "base", preserved: false } }));
+  });
+
+  it("preserves existing valid baseCommitSha across sessions", async () => {
+    mockedExecSync.mockReturnValue("");
+    const store = createMockStore();
+    const executor = new TaskExecutor(store, "/tmp/test");
+    const audit = { git: vi.fn().mockResolvedValue(undefined) };
+
+    await (executor as any).captureBaseCommitSha(makeTask({ baseCommitSha: "old123" }), "/tmp/test/.worktrees/fn-4383", audit);
+
+    expect(store.updateTask).not.toHaveBeenCalled();
+    expect(audit.git).toHaveBeenCalledWith(expect.objectContaining({ metadata: { purpose: "base", preserved: true } }));
+  });
+
+  it("recaptures when existing baseCommitSha is not ancestor", async () => {
+    mockedExecSync.mockImplementation(() => {
+      throw new Error("not ancestor");
+    });
+    mockedExec.mockImplementation((cmd: any, _opts: any, cb: any) => cb(null, cmd.includes("merge-base") ? "new456\n" : ""));
+    const store = createMockStore();
+    const executor = new TaskExecutor(store, "/tmp/test");
+    const audit = { git: vi.fn().mockResolvedValue(undefined) };
+
+    await (executor as any).captureBaseCommitSha(makeTask({ baseCommitSha: "stale999" }), "/tmp/test/.worktrees/fn-4383", audit);
+
+    expect(store.updateTask).toHaveBeenCalledWith("FN-4383", { baseCommitSha: "new456" });
+  });
+
+  it("preserves prior merge base for FN-4309/FN-4383 multi-session regression", async () => {
+    mockedExecSync.mockReturnValue("");
+    const store = createMockStore();
+    const executor = new TaskExecutor(store, "/tmp/test");
+    const audit = { git: vi.fn().mockResolvedValue(undefined) };
+
+    await (executor as any).captureBaseCommitSha(makeTask({ baseCommitSha: "merge_base_sha" }), "/tmp/test/.worktrees/fn-4383", audit);
+
+    expect(store.updateTask).not.toHaveBeenCalled();
+    expect(audit.git).toHaveBeenCalledWith(expect.objectContaining({ metadata: { purpose: "base", preserved: true } }));
+  });
+
+  it("falls back to HEAD when merge-base fails", async () => {
+    mockedExec.mockImplementation((cmd: any, _opts: any, cb: any) => {
+      if (String(cmd).includes("merge-base")) {
+        cb(new Error("merge-base failed"), "", "merge-base failed");
+        return;
+      }
+      cb(null, "head777\n", "");
+    });
+    const store = createMockStore();
+    const executor = new TaskExecutor(store, "/tmp/test");
+    const audit = { git: vi.fn().mockResolvedValue(undefined) };
+
+    await (executor as any).captureBaseCommitSha(makeTask(), "/tmp/test/.worktrees/fn-4383", audit);
+
+    expect(store.updateTask).toHaveBeenCalledWith("FN-4383", { baseCommitSha: "head777" });
+    expect(vi.mocked(executorLog.warn)).toHaveBeenCalledWith(expect.stringContaining("falling back to HEAD"));
+  });
+});