perf(test): reuse the CI scope Git baseline

Copy a pristine repository into each case-owned workspace instead of repeating init, add, commit and rev-parse for 47 identical baselines. Keep every scenario mutation and real planner invocation, with seed cleanup owned by the file.

tests/boundary/filesystem/ciChangeScope.test.ts

@@ -1,11 +1,22 @@
-import { mkdir, readFile, readdir, rename, writeFile } from "node:fs/promises";
+import {
+  cp,
+  mkdir,
+  readFile,
+  readdir,
+  rename,
+  writeFile,
+} from "node:fs/promises";
 import { dirname, join } from "node:path";
 
-import { expect, it } from "vitest";
+import { afterAll, beforeAll, expect, it } from "vitest";
 import { parse } from "yaml";
 import { z } from "zod";
 
 import { createTestTempDirectory } from "../../fixtures/temporaryDirectory.js";
+import {
+  createTestWorkspace,
+  removeTestWorkspace,
+} from "../../support/workspace/workspaceFixture.js";
 import {
   executeWorkflowFixture as execFileAsync,
   workflowGit as git,
@@ -30,15 +41,35 @@ async function change(
   return commit(directory);
 }
 
-async function fixture() {
-  const directory = await createTestTempDirectory("rea-ci-scope-");
+let seed: { directory: string; base: string } | undefined;
+let seedWorkspaceRoot: string | undefined;
+
+beforeAll(async () => {
+  const workspace = await createTestWorkspace("rea-ci-scope-seed-");
+  seedWorkspaceRoot = workspace.root;
+  const directory = await workspace.mkdir("repository");
   await git(directory, ["init", "--initial-branch=main"]);
   const base = await change(
     directory,
     ["src/provider.ts", "README.md"],
     "Initial fixture content\n",
   );
-  return { directory, base };
+  seed = { directory, base };
+});
+
+afterAll(async () => {
+  if (seedWorkspaceRoot !== undefined)
+    await removeTestWorkspace(seedWorkspaceRoot);
+});
+
+async function fixture() {
+  const initial = seed;
+  if (initial === undefined)
+    throw new Error("CI scope seed was not initialized");
+  const directory = await createTestTempDirectory("rea-ci-scope-");
+  // Copy the pristine object database, refs and index; each case owns its mutations.
+  await cp(initial.directory, directory, { recursive: true });
+  return { directory, base: initial.base };
 }
 
 async function classify(