fix(FN-4383): align pooled worktree baseline tests with merge-base capture

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

packages/engine/src/__tests__/executor-worktree.test.ts

@@ -26,6 +26,7 @@ import {
   mockedFindWorktreeUser,
   mockedStepSessionExecutor,
   mockedWithRateLimitRetry,
+  mockedExec,
   mockedExecSync,
   mockedExistsSync,
   mockedHydrateWorktreeDb,
@@ -1898,11 +1899,18 @@ describe("TaskExecutor worktree pool integration", () => {
     mockedExistsSync.mockImplementation((p) => p === "/tmp/test/.worktrees/idle-wt");
 
     mockedExecSync.mockImplementation((cmd: any) => {
-      if (String(cmd) === "git rev-parse HEAD") {
-        return "newbase123\n" as any;
+      if (String(cmd).includes("git merge-base --is-ancestor")) {
+        throw new Error("not ancestor");
       }
       return "" as any;
     });
+    mockedExec.mockImplementation((cmd: any, _opts: any, cb: any) => {
+      if (String(cmd).includes("git merge-base HEAD origin/main")) {
+        cb(null, "newbase123\n", "");
+        return;
+      }
+      cb(null, "", "");
+    });
 
     const store = createMockStore();
     store.getTask.mockResolvedValue({

packages/engine/src/executor.ts

@@ -5662,7 +5662,7 @@ ${failureFeedback}
         baseCommitSha = stdout.trim() || undefined;
       } catch (err: unknown) {
         const errorMessage = err instanceof Error ? err.message : String(err);
-        executorLog.warn(`${task.id}: merge-base failed for ${task.id}, falling back to HEAD: ${errorMessage}`);
+        executorLog.warn(`${task.id}: merge-base failed, falling back to HEAD: ${errorMessage}`);
       }
 
       if (!baseCommitSha) {