Fix session persistence: flush all buffered entries on first assistant message

- SessionManager: add flushed flag, _persist() flushes all entries when first assistant seen
- SessionManager: reset() now creates session header
- MomSessionManager: same pattern, remove pendingEntries/sessionInitialized/startSession/shouldInitializeSession

packages/mom/src/agent.ts

@@ -411,12 +411,7 @@ function createRunner(sandboxConfig: SandboxConfig, channelId: string, channelDi
 	const systemPrompt = buildSystemPrompt(workspacePath, channelId, memory, sandboxConfig, [], [], skills);
 
 	// Create session manager and settings manager
-	// Pass model info so new sessions get a header written immediately
-	const sessionManager = new MomSessionManager(channelDir, {
-		provider: model.provider,
-		id: model.id,
-		thinkingLevel: "off",
-	});
+	const sessionManager = new MomSessionManager(channelDir);
 	const settingsManager = new MomSettingsManager(join(channelDir, ".."));
 
 	// Create agent