Squashed 'src/pi/' content from commit d981de122

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

packages/coding-agent/test/suite/regressions/8328-zero-usage-auto-compaction.test.ts

@@ -0,0 +1,80 @@
+import type { AssistantMessage } from "@earendil-works/pi-ai";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { createHarness, type Harness } from "../harness.ts";
+
+type SessionWithCompactionInternals = {
+	_checkCompaction: (assistantMessage: AssistantMessage) => Promise<boolean>;
+	_runAutoCompaction: (reason: "overflow" | "threshold", willRetry: boolean) => Promise<boolean>;
+};
+
+function createZeroUsageAssistant(harness: Harness): AssistantMessage {
+	const model = harness.getModel();
+	return {
+		role: "assistant",
+		content: [{ type: "text", text: "response" }],
+		api: model.api,
+		provider: model.provider,
+		model: model.id,
+		usage: {
+			input: 0,
+			output: 0,
+			cacheRead: 0,
+			cacheWrite: 0,
+			totalTokens: 0,
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+		},
+		stopReason: "stop",
+		timestamp: Date.now(),
+	};
+}
+
+describe("issue #8328 zero-usage auto-compaction", () => {
+	const harnesses: Harness[] = [];
+
+	afterEach(() => {
+		vi.restoreAllMocks();
+		while (harnesses.length > 0) {
+			harnesses.pop()?.cleanup();
+		}
+	});
+
+	async function createCompactionHarness(): Promise<Harness> {
+		const harness = await createHarness({
+			models: [{ id: "faux-1", contextWindow: 100, maxTokens: 20 }],
+			settings: { compaction: { enabled: true, reserveTokens: 10 } },
+		});
+		harnesses.push(harness);
+		return harness;
+	}
+
+	it("uses the message estimate when no assistant has reported usage", async () => {
+		const harness = await createCompactionHarness();
+		const assistant = createZeroUsageAssistant(harness);
+		harness.session.agent.state.messages = [
+			{ role: "user", content: [{ type: "text", text: "x".repeat(400) }], timestamp: Date.now() - 1 },
+			assistant,
+		];
+		const sessionInternals = harness.session as unknown as SessionWithCompactionInternals;
+		const runAutoCompactionSpy = vi.spyOn(sessionInternals, "_runAutoCompaction").mockResolvedValue(false);
+
+		await sessionInternals._checkCompaction(assistant);
+
+		expect(runAutoCompactionSpy).toHaveBeenCalledOnce();
+		expect(runAutoCompactionSpy).toHaveBeenCalledWith("threshold", false);
+	});
+
+	it("does not compact when the zero-usage message estimate is below the threshold", async () => {
+		const harness = await createCompactionHarness();
+		const assistant = createZeroUsageAssistant(harness);
+		harness.session.agent.state.messages = [
+			{ role: "user", content: [{ type: "text", text: "short" }], timestamp: Date.now() - 1 },
+			assistant,
+		];
+		const sessionInternals = harness.session as unknown as SessionWithCompactionInternals;
+		const runAutoCompactionSpy = vi.spyOn(sessionInternals, "_runAutoCompaction").mockResolvedValue(false);
+
+		await sessionInternals._checkCompaction(assistant);
+
+		expect(runAutoCompactionSpy).not.toHaveBeenCalled();
+	});
+});