fix(prompt): document filesystem task lock contract

tests/eval/task-api-docs-contract.test.ts

@@ -0,0 +1,15 @@
+import { readFile } from "node:fs/promises";
+import { join } from "node:path";
+import { describe, expect, it } from "vitest";
+
+const TASK_API_DOC = join(__dirname, "../../src/main/prompt-builder/api-docs/tasks.en.md");
+
+describe("task API prompt contract", () => {
+  it("documents requiresFilesystem for code and workspace task creation", async () => {
+    const doc = await readFile(TASK_API_DOC, "utf8");
+
+    expect(doc).toContain('"requiresFilesystem": true');
+    expect(doc).toContain("Set requiresFilesystem=true for code, file, repository, build, test, or local workspace work.");
+    expect(doc).toMatch(/Implement user auth[\s\S]*"requiresFilesystem":true/);
+  });
+});