test(session): pin no-authority nested managed reads on every platform

packages/coding-agent/test/session/managed-nested-read-pin.test.ts

@@ -0,0 +1,93 @@
+/**
+ * Pins the no-authority nested-read contract of
+ * `ManagedSessionDescendantStore.readExpected`.
+ *
+ * History: the deny-guard `#assertPathBackedReadRelative` was added to
+ * `readExpected` by 8cc57de1fa, removed in favor of the per-component
+ * `#assertPathBackedDirectoryChain` walk by #4188 (79e4e0a097), then
+ * re-added by the drive-by 23261d448f — breaking every nested managed read
+ * (fork artifact copy, moveTo topology, session-import verification) on
+ * Darwin, where retained descriptor authority does not exist. Ubuntu-only CI
+ * cannot catch a fourth flip: on Linux the constructor always retains root
+ * authority (crates/pi-natives RecoveryFsRoot is Linux-only), so the guard
+ * never fires there. These tests spoof the Darwin authority absence on every
+ * platform so the restored contract stays pinned where CI runs.
+ */
+import { afterEach, describe, expect, it } from "bun:test";
+import * as fs from "node:fs";
+import * as fsp from "node:fs/promises";
+import * as os from "node:os";
+import * as path from "node:path";
+import {
+	ManagedSessionDescendantStore,
+	managedDirectoryRoot,
+} from "../../src/session/internal/managed-session-storage";
+
+const temporaryDirectories: string[] = [];
+
+afterEach(async () => {
+	await Promise.all(temporaryDirectories.splice(0).map(dir => fsp.rm(dir, { recursive: true, force: true })));
+});
+
+/**
+ * Builds a store whose constructor observed a non-Linux platform, so it holds
+ * no retained root authority — the Darwin condition on every CI runner is
+ * spoofable only in this direction (Linux authority can be withheld, never
+ * granted on Darwin). The spoof covers construction only, matching the
+ * established pattern in managed-append-darwin-ctime.test.ts.
+ */
+function createStoreWithoutAuthority(): { store: ManagedSessionDescendantStore; baseDir: string } {
+	const baseDir = fs.mkdtempSync(path.join(os.tmpdir(), "gjc-nested-read-pin-"));
+	temporaryDirectories.push(baseDir);
+	fs.chmodSync(baseDir, 0o700);
+	const platformDescriptor = Object.getOwnPropertyDescriptor(process, "platform");
+	let store: ManagedSessionDescendantStore;
+	try {
+		Object.defineProperty(process, "platform", { configurable: true, value: "darwin" });
+		store = new ManagedSessionDescendantStore(managedDirectoryRoot(baseDir), baseDir);
+	} finally {
+		if (platformDescriptor) Object.defineProperty(process, "platform", platformDescriptor);
+	}
+	return { store, baseDir };
+}
+
+/** Publishes nested bytes with the real platform active (publishing is not under test). */
+function publishNested(store: ManagedSessionDescendantStore, relativePath: string, text: string): Uint8Array {
+	const bytes = Buffer.from(text, "utf8");
+	store.publishNoReplaceSync(relativePath, bytes);
+	return bytes;
+}
+
+describe("ManagedSessionDescendantStore.readExpected nested reads without retained authority", () => {
+	it("returns exact nested bytes and identity instead of managed_nested_path_unsupported", () => {
+		const { store } = createStoreWithoutAuthority();
+		const text = '{"type":"session","id":"nested-read-pin"}\n';
+		publishNested(store, "artifacts/kept.txt", text);
+
+		const snapshot = store.readExpected("artifacts/kept.txt");
+
+		expect(snapshot).not.toBeNull();
+		expect(snapshot?.bytes.toString("utf8")).toBe(text);
+		const onDisk = fs.readFileSync(path.join(store.dir, "artifacts", "kept.txt"));
+		expect(snapshot?.identity.sha256).toBe(new Bun.CryptoHasher("sha256").update(onDisk).digest("hex"));
+	});
+
+	it("returns null for a missing nested leaf without throwing", () => {
+		const { store } = createStoreWithoutAuthority();
+		publishNested(store, "artifacts/kept.txt", "present");
+
+		expect(store.readExpected("artifacts/missing.txt")).toBeNull();
+	});
+
+	it("still rejects a symlinked intermediate directory via the per-component chain walk", async () => {
+		const { store, baseDir } = createStoreWithoutAuthority();
+		publishNested(store, "artifacts/kept.txt", "present");
+		const outside = path.join(baseDir, "outside");
+		fs.mkdirSync(outside, { mode: 0o700 });
+		fs.writeFileSync(path.join(outside, "escape.txt"), "attacker");
+		fs.rmSync(path.join(store.dir, "artifacts"), { recursive: true });
+		fs.symlinkSync(outside, path.join(store.dir, "artifacts"));
+
+		expect(() => store.readExpected("artifacts/escape.txt")).toThrow();
+	});
+});