chore(vendor): import pi 0.85.1

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

third_party/pi/packages/agent/test/harness/runtime/test-utils.ts

@@ -0,0 +1,32 @@
+import { BACKGROUND_CONTEXT } from "../../../src/harness/context.ts";
+import { MemoryStorage } from "../../../src/harness/session/memory.ts";
+import type { CommitResult, Write } from "../../../src/harness/session/types.ts";
+
+export class FailingMemoryStorage extends MemoryStorage {
+	failure: Error | undefined;
+
+	override commit(writes: Write[]) {
+		const failure = this.failure;
+		this.failure = undefined;
+		return failure === undefined ? super.commit(writes, BACKGROUND_CONTEXT) : Promise.reject(failure);
+	}
+}
+
+export class ControlledMemoryStorage extends MemoryStorage {
+	beforeNextCommit: (() => Promise<void>) | undefined;
+
+	override async commit(writes: Write[]): Promise<CommitResult> {
+		const beforeCommit = this.beforeNextCommit;
+		this.beforeNextCommit = undefined;
+		await beforeCommit?.();
+		return super.commit(writes, BACKGROUND_CONTEXT);
+	}
+}
+
+export function deferred(): { promise: Promise<void>; resolve(): void } {
+	let resolvePromise: (() => void) | undefined;
+	const promise = new Promise<void>((resolve) => {
+		resolvePromise = resolve;
+	});
+	return { promise, resolve: () => resolvePromise?.() };
+}