fix(agent): seeded startup learned memory snapshot

Use the pre-session memory prompt snapshot as the learned.md baseline when startup consolidation refreshes before a session-scoped cache exists. This keeps active-session learn writes out of the refreshed prompt while still surfacing the new consolidated summary.

Refs #3743

packages/coding-agent/src/memories/index.ts

@@ -166,6 +166,11 @@ const memoryToolDeveloperInstructionsBySession = new WeakMap<
 	MemoryInstructionSession,
 	CachedMemoryToolDeveloperInstructions
 >();
+const memoryToolDeveloperInstructionsByRoot = new Map<string, MemoryToolDeveloperInstructionsSnapshot | undefined>();
+
+function getMemoryInstructionRoot(agentDir: string, settings: Settings): string {
+	return getMemoryRoot(agentDir, settings.getCwd());
+}
 
 function getMemoryInstructionSessionFile(session: MemoryInstructionSession): string | undefined {
 	return session.sessionManager.getSessionFile() ?? undefined;
@@ -177,7 +182,7 @@ async function readMemoryToolDeveloperInstructionsSnapshot(
 ): Promise<MemoryToolDeveloperInstructionsSnapshot | undefined> {
 	const cfg = loadMemoryConfig(settings);
 	if (!cfg.enabled) return undefined;
-	const memoryRoot = getMemoryRoot(agentDir, settings.getCwd());
+	const memoryRoot = getMemoryInstructionRoot(agentDir, settings);
 
 	let summary = "";
 	try {
@@ -255,8 +260,10 @@ export async function refreshMemoryToolDeveloperInstructionsCacheAfterStartup(
 	const sessionFile = getMemoryInstructionSessionFile(session);
 	const cached = memoryToolDeveloperInstructionsBySession.get(session);
 	const current = await readMemoryToolDeveloperInstructionsSnapshot(agentDir, settings);
+	const root = getMemoryInstructionRoot(agentDir, settings);
+	const baseline = memoryToolDeveloperInstructionsByRoot.get(root);
 	const cachedLearned = cached && cached.sessionFile === sessionFile ? cached.snapshot?.learned : undefined;
-	const learned = cachedLearned ?? current?.learned ?? "";
+	const learned = cachedLearned ?? baseline?.learned ?? "";
 	const snapshot = current ? { summary: current.summary, learned } : undefined;
 	cacheMemoryToolDeveloperInstructions(session, sessionFile, snapshot, settings);
 }
@@ -271,6 +278,7 @@ export async function buildMemoryToolDeveloperInstructions(
 ): Promise<string | undefined> {
 	if (!session) {
 		const snapshot = await readMemoryToolDeveloperInstructionsSnapshot(agentDir, settings);
+		memoryToolDeveloperInstructionsByRoot.set(getMemoryInstructionRoot(agentDir, settings), snapshot);
 		return renderMemoryToolDeveloperInstructionsSnapshot(snapshot, settings);
 	}
 

packages/coding-agent/test/autolearn-learn-local.test.ts

@@ -198,13 +198,15 @@ describe("learned-lesson read-back", () => {
 		expect(await buildMemoryToolDeveloperInstructions(agentDir, settings, session)).toBeUndefined();
 	});
 
-	it("refreshes consolidated summaries without rereading learned lessons from the active session", async () => {
+	it("uses the pre-session learned snapshot when startup refresh has no session cache yet", async () => {
 		const settings = Settings.isolated({ "memory.backend": "local" });
-		const session = sessionWithFile("session-consolidate.jsonl");
-		// First build (before background consolidation finishes) snapshots an empty learned.md.
-		expect(await buildMemoryToolDeveloperInstructions(agentDir, settings, session)).toBeUndefined();
+		await saveLearnedLesson(agentDir, settings.getCwd(), { content: "Prior-session lesson" });
+		const initial = await buildMemoryToolDeveloperInstructions(agentDir, settings);
+		expect(initial).toContain("Prior-session lesson");
 
-		// The active session learns while the background pipeline is still running.
+		const session = sessionWithFile("session-consolidate.jsonl");
+		// The active session learns while the background pipeline is still running,
+		// before any session-scoped prompt rebuild has populated the WeakMap.
 		await saveLearnedLesson(agentDir, settings.getCwd(), { content: "Active-session lesson" });
 		// Background pipeline writes the consolidated summary later.
 		const root = getMemoryRoot(agentDir, settings.getCwd());
@@ -213,6 +215,7 @@ describe("learned-lesson read-back", () => {
 		await refreshMemoryToolDeveloperInstructionsCacheAfterStartup(session, agentDir, settings);
 		const out = await buildMemoryToolDeveloperInstructions(agentDir, settings, session);
 		expect(out).toContain("Consolidated guidance here.");
+		expect(out).toContain("Prior-session lesson");
 		expect(out).not.toContain("Active-session lesson");
 
 		const nextSession = sessionWithFile("session-after-consolidate.jsonl");