feat(FN-4518): complete Step 2 — persist rebase merge base SHA

Fusion-Task-Id: FN-4518
Fusion-Task-Lineage: 48749dec-b2c9-484b-a13e-ffacc1fa9014

packages/engine/src/__tests__/merger-rebase-base-sha.test.ts

@@ -0,0 +1,170 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("../pi.js", () => ({
+  createFnAgent: vi.fn().mockResolvedValue({
+    session: {
+      prompt: vi.fn().mockResolvedValue(undefined),
+      dispose: vi.fn(),
+    },
+  }),
+  describeModel: vi.fn(() => "mock-provider/mock-model"),
+  promptWithFallback: vi.fn(async (session, prompt, options) => {
+    if (options === undefined) await session.prompt(prompt);
+    else await session.prompt(prompt, options);
+  }),
+  compactSessionContext: vi.fn(),
+}));
+
+vi.mock("node:fs", () => ({
+  existsSync: vi.fn().mockReturnValue(false),
+  readFileSync: vi.fn(),
+}));
+
+vi.mock("node:child_process", async () => {
+  const { promisify } = await import("node:util");
+  const execSyncFn = vi.fn();
+  const execFn: any = vi.fn((cmd: any, opts: any, cb: any) => {
+    const callback = typeof opts === "function" ? opts : cb;
+    try {
+      const out = execSyncFn(cmd, { stdio: ["pipe", "pipe", "pipe"] });
+      callback?.(null, out?.toString?.() ?? "", "");
+    } catch (err: any) {
+      callback?.(err, err?.stdout?.toString?.() ?? "", err?.stderr?.toString?.() ?? "");
+    }
+  });
+  execFn[promisify.custom] = (cmd: any, opts?: any) =>
+    new Promise((resolve, reject) => {
+      execFn(cmd, opts, (err: any, stdout: any, stderr: any) => {
+        if (err) {
+          err.stdout = stdout;
+          err.stderr = stderr;
+          reject(err);
+        } else {
+          resolve({ stdout, stderr });
+        }
+      });
+    });
+
+  const execFileFn: any = vi.fn((file: any, args: any, opts: any, cb: any) => {
+    const callback = typeof opts === "function" ? opts : cb;
+    const options = typeof opts === "function" ? {} : opts;
+    const cmd = [file, ...(Array.isArray(args) ? args : [])].join(" ");
+    try {
+      const out = execSyncFn(cmd, { stdio: ["pipe", "pipe", "pipe"], ...options });
+      callback?.(null, out?.toString?.() ?? "", "");
+    } catch (err: any) {
+      callback?.(err, err?.stdout?.toString?.() ?? "", err?.stderr?.toString?.() ?? "");
+    }
+  });
+  execFileFn[promisify.custom] = (file: any, args?: any, opts?: any) =>
+    new Promise((resolve, reject) => {
+      execFileFn(file, args, opts, (err: any, stdout: any, stderr: any) => {
+        if (err) {
+          err.stdout = stdout;
+          err.stderr = stderr;
+          reject(err);
+        } else {
+          resolve({ stdout, stderr });
+        }
+      });
+    });
+
+  return { execSync: execSyncFn, exec: execFn, execFile: execFileFn };
+});
+
+import { execSync } from "node:child_process";
+import { DEFAULT_SETTINGS, type Task, type TaskStore } from "@fusion/core";
+import { aiMergeTask } from "../merger.js";
+
+const mockedExecSync = vi.mocked(execSync);
+
+function createMockStore(overrides: Partial<TaskStore> = {}): TaskStore {
+  const task: Task = {
+    id: "FN-050",
+    title: "Test task",
+    description: "Test",
+    column: "in-review",
+    dependencies: [],
+    worktree: "/tmp/root/.worktrees/KB-050",
+    steps: [],
+    currentStep: 0,
+    log: [],
+    createdAt: new Date().toISOString(),
+    updatedAt: new Date().toISOString(),
+  };
+  return {
+    getTask: vi.fn().mockResolvedValue({ ...task, prompt: "# test" }),
+    listTasks: vi.fn().mockResolvedValue([{ id: task.id, worktree: task.worktree, column: "in-review" }]),
+    updateTask: vi.fn().mockResolvedValue(task),
+    moveTask: vi.fn().mockResolvedValue(task),
+    logEntry: vi.fn().mockResolvedValue(undefined),
+    appendAgentLog: vi.fn().mockResolvedValue(undefined),
+    updateSettings: vi.fn().mockResolvedValue({}),
+    getSettings: vi.fn().mockResolvedValue({ ...DEFAULT_SETTINGS }),
+    getActiveMergingTask: vi.fn().mockReturnValue(null),
+    emit: vi.fn(),
+    on: vi.fn(),
+    clearStaleExecutionStartBranchReferences: vi.fn().mockReturnValue([]),
+    getVerificationCacheHit: vi.fn().mockReturnValue(null),
+    recordVerificationCachePass: vi.fn(),
+    ...overrides,
+  } as unknown as TaskStore;
+}
+
+describe("aiMergeTask rebaseBaseSha persistence", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("stores rebaseBaseSha for rebase-routed merges", async () => {
+    const store = createMockStore({
+      getSettings: vi.fn().mockResolvedValue({ ...DEFAULT_SETTINGS, directMergeCommitStrategy: "always-rebase" }),
+    });
+
+    mockedExecSync.mockImplementation((cmd: any) => {
+      const cmdStr = String(cmd);
+      if (cmdStr.includes("rev-parse --verify")) return Buffer.from("abc123");
+      if (cmdStr === "git rev-parse HEAD" || cmdStr.startsWith("git rev-parse HEAD ")) return "rebasemergedsha";
+      if (cmdStr.includes("git log")) return "- feat: something";
+      if (cmdStr.includes("merge-base")) return Buffer.from("abc123");
+      if (cmdStr.includes("rev-parse \"abc123\"")) return "rebasebase123";
+      if (cmdStr.includes("rev-list --reverse \"rebasebase123..fusion/FN-050\"")) return "";
+      if (cmdStr.includes("status --porcelain")) return "";
+      if (cmdStr.includes("rev-parse --git-path CHERRY_PICK_HEAD")) return ".git/CHERRY_PICK_HEAD";
+      if (cmdStr.includes("rev-parse --git-path sequencer")) return ".git/sequencer";
+      if (cmdStr.includes("diff --shortstat \"rebasebase123..HEAD\"")) return "2 files changed, 5 insertions(+), 1 deletions(-)";
+      if (cmdStr.includes("branch -d") || cmdStr.includes("branch -D")) return Buffer.from("");
+      if (cmdStr.includes("worktree remove")) return Buffer.from("");
+      return Buffer.from("");
+    });
+
+    await aiMergeTask(store, "/tmp/root", "FN-050");
+    const mergeDetailsCall = (store.updateTask as ReturnType<typeof vi.fn>).mock.calls.find((call: any[]) => call[1]?.mergeDetails);
+    expect(mergeDetailsCall?.[1].mergeDetails.rebaseBaseSha).toBe("rebasebase123");
+  });
+
+  it("leaves rebaseBaseSha undefined for squash merges", async () => {
+    const store = createMockStore();
+
+    mockedExecSync.mockImplementation((cmd: any) => {
+      const cmdStr = String(cmd);
+      if (cmdStr.includes("rev-parse --verify")) return Buffer.from("abc123");
+      if (cmdStr === "git rev-parse HEAD" || cmdStr.startsWith("git rev-parse HEAD ")) return "mergedcommit123456789";
+      if (cmdStr.includes("git log")) return "- feat: something";
+      if (cmdStr.includes("merge-base")) return Buffer.from("abc123");
+      if (cmdStr.includes("--stat")) return "1 file changed";
+      if (cmdStr.includes("merge --squash")) return Buffer.from("");
+      if (cmdStr.includes("diff --name-only --diff-filter=U")) return "";
+      if (cmdStr.includes("diff --cached --quiet")) return "1";
+      if (cmdStr.includes("git commit")) return Buffer.from("");
+      if (cmdStr.includes("show --shortstat")) return "1 file changed, 1 insertion(+)";
+      if (cmdStr.includes("branch -d") || cmdStr.includes("branch -D")) return Buffer.from("");
+      if (cmdStr.includes("worktree remove")) return Buffer.from("");
+      return Buffer.from("");
+    });
+
+    await aiMergeTask(store, "/tmp/root", "FN-050");
+    const mergeDetailsCall = (store.updateTask as ReturnType<typeof vi.fn>).mock.calls.find((call: any[]) => call[1]?.mergeDetails);
+    expect(mergeDetailsCall?.[1].mergeDetails.rebaseBaseSha).toBeUndefined();
+  });
+});