test(gsd): add worktree main_branch preference test

src/resources/extensions/gsd/tests/worktree-main-branch.test.ts

@@ -0,0 +1,20 @@
+/**
+ * Regression test for #3461: createAutoWorktree must use git.main_branch
+ * preference when META.json integration branch is absent.
+ */
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+test("auto-worktree.ts includes main_branch preference in startPoint fallback (#3461)", () => {
+  const src = readFileSync(
+    join(import.meta.dirname, "..", "auto-worktree.ts"),
+    "utf-8",
+  );
+  // The fix adds gitPrefs?.main_branch to the startPoint fallback chain
+  assert.ok(
+    src.includes("gitPrefs?.main_branch") || src.includes("prefs.main_branch"),
+    "createAutoWorktree must check git.main_branch preference before falling back to nativeDetectMainBranch",
+  );
+});