Phase 6: add compaction coexistence hint — one-time notify when both compactors run.

Shows ui.notify once when pi-auto-compact is detected while Pi compaction.enabled stays true.

Co-authored-by: Cursor <cursoragent@cursor.com>

test/auto-compact.test.ts

@@ -2,8 +2,10 @@ import { describe, expect, it } from "vitest";
 import {
 	detectAndCachePiAutoCompact,
 	detectPiAutoCompact,
+	maybeNotifyCompactionCoexistenceHint,
 	PI_AUTO_COMPACT_FOLLOW_UP_PREFIXES,
 	resolveDeliveryMode,
+	resolvePiDefaultCompactionEnabled,
 } from "../src/auto-compact";
 import { createDefaultSettings } from "../src/settings";
 import { createRuntimeFlags } from "../src/state";
@@ -53,3 +55,54 @@ describe("PI_AUTO_COMPACT_FOLLOW_UP_PREFIXES", () => {
 		]);
 	});
 });
+
+describe("resolvePiDefaultCompactionEnabled", () => {
+	it("defaults to enabled when compaction settings are absent", () => {
+		expect(resolvePiDefaultCompactionEnabled({}, {})).toBe(true);
+	});
+
+	it("lets project override global compaction.enabled", () => {
+		expect(
+			resolvePiDefaultCompactionEnabled(
+				{ compaction: { enabled: true } },
+				{ compaction: { enabled: false } },
+			),
+		).toBe(false);
+	});
+});
+
+describe("maybeNotifyCompactionCoexistenceHint", () => {
+	it("notifies once when pi-auto-compact and Pi compaction are both active", () => {
+		const runtime = createRuntimeFlags();
+		runtime.autoCompactDetected = true;
+		const notifications: string[] = [];
+		const ctx = {
+			hasUI: true,
+			ui: {
+				notify: (message: string) => {
+					notifications.push(message);
+				},
+			},
+		};
+
+		maybeNotifyCompactionCoexistenceHint(ctx as never, runtime, true);
+		maybeNotifyCompactionCoexistenceHint(ctx as never, runtime, true);
+
+		expect(notifications).toHaveLength(1);
+		expect(runtime.compactionCoexistenceHintShown).toBe(true);
+	});
+
+	it("skips notify when pi-auto-compact is not detected", () => {
+		const runtime = createRuntimeFlags();
+		const notifications: string[] = [];
+		const ctx = {
+			hasUI: true,
+			ui: { notify: (message: string) => notifications.push(message) },
+		};
+
+		maybeNotifyCompactionCoexistenceHint(ctx as never, runtime, true);
+
+		expect(notifications).toHaveLength(0);
+		expect(runtime.compactionCoexistenceHintShown).toBe(false);
+	});
+});