Squashed 'src/pi/' content from commit d981de122

git-subtree-dir: src/pi
git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

packages/agent/test/harness/mutation-line.test.ts

@@ -0,0 +1,66 @@
+import { describe, expect, it } from "vitest";
+import { MutationLine } from "../../src/harness/session/mutation-line.ts";
+
+function deferred(): { promise: Promise<void>; resolve(): void } {
+	let resolvePromise!: () => void;
+	const promise = new Promise<void>((resolve) => {
+		resolvePromise = resolve;
+	});
+	return { promise, resolve: resolvePromise };
+}
+
+describe("MutationLine", () => {
+	it("serializes every Session mutation", async () => {
+		const line = new MutationLine();
+		const gate = deferred();
+		const order: string[] = [];
+		const first = line.run(async () => {
+			order.push("first:start");
+			await gate.promise;
+			order.push("first:end");
+			return "first";
+		});
+		const second = line.run(() => {
+			order.push("second");
+			return "second";
+		});
+
+		await Promise.resolve();
+		expect(order).toEqual(["first:start"]);
+		gate.resolve();
+		await expect(first).resolves.toBe("first");
+		await expect(second).resolves.toBe("second");
+		expect(order).toEqual(["first:start", "first:end", "second"]);
+	});
+
+	it("continues after a failed job while preserving the original failure", async () => {
+		const line = new MutationLine();
+		const rejection = new Error("mutation failed");
+
+		await expect(
+			line.run(() => {
+				throw rejection;
+			}),
+		).rejects.toBe(rejection);
+		await expect(line.run(() => "next")).resolves.toBe("next");
+	});
+
+	it("seals queued and future jobs while draining the running job", async () => {
+		const line = new MutationLine();
+		const gate = deferred();
+		const running = line.run(async () => {
+			await gate.promise;
+			return "running";
+		});
+		await Promise.resolve();
+		const queued = line.run(() => "queued");
+		const closed = new Error("closed");
+
+		const drained = line.seal(closed);
+		await expect(line.run(() => "late")).rejects.toBe(closed);
+		gate.resolve();
+		await expect(running).resolves.toBe("running");
+		await expect(queued).rejects.toBe(closed);
+		await drained;
+	});
+});