feat: serialize command auto-replies with queue

src/process/command-queue.test.ts

@@ -0,0 +1,58 @@
+import { describe, expect, it } from "vitest";
+
+import { enqueueCommand, getQueueSize } from "./command-queue.js";
+
+describe("command queue", () => {
+	it("runs tasks one at a time in order", async () => {
+		let active = 0;
+		let maxActive = 0;
+		const calls: number[] = [];
+
+		const makeTask = (id: number) => async () => {
+			active += 1;
+			maxActive = Math.max(maxActive, active);
+			calls.push(id);
+			await new Promise((resolve) => setTimeout(resolve, 15));
+			active -= 1;
+			return id;
+		};
+
+		const results = await Promise.all([
+			enqueueCommand(makeTask(1)),
+			enqueueCommand(makeTask(2)),
+			enqueueCommand(makeTask(3)),
+		]);
+
+		expect(results).toEqual([1, 2, 3]);
+		expect(calls).toEqual([1, 2, 3]);
+		expect(maxActive).toBe(1);
+		expect(getQueueSize()).toBe(0);
+	});
+
+	it("invokes onWait callback when a task waits past the threshold", async () => {
+		let waited: number | null = null;
+		let queuedAhead: number | null = null;
+
+		// First task holds the queue long enough to trigger wait notice.
+		const first = enqueueCommand(async () => {
+			await new Promise((resolve) => setTimeout(resolve, 30));
+		});
+
+		const second = enqueueCommand(
+			async () => {},
+			{
+				warnAfterMs: 5,
+				onWait: (ms, ahead) => {
+					waited = ms;
+					queuedAhead = ahead;
+				},
+			},
+		);
+
+		await Promise.all([first, second]);
+
+		expect(waited).not.toBeNull();
+		expect((waited as number)).toBeGreaterThanOrEqual(5);
+		expect(queuedAhead).toBe(0);
+	});
+});