Wave 0: shared contracts + extension points

- src/core/contracts.ts: plan tree / graph / ledger / job protocol / artifact
  registry types — the single source of truth for all workstreams
- tools: per-request factory createTeacherTools({chatId}) composing
  questionTools + planTools (stub) + jobTools (stub); quiz gains nodeId
- prompt composition: system-prompt.md + sorted src/agent/prompts/*.md
- ChatRecord.tree + saveTree; pending gate scoped to quiz/ask (+findPendingJobCall)
- chat.tsx: artifact renderer extension point + ChatActionsContext.syncFromServer

src/server/chat-handler.ts

@@ -1,5 +1,6 @@
 import { createAgentUIStreamResponse, type UIMessage } from "ai";
 import { createTeacherAgent, type TeacherAgent } from "../agent/teacher-agent.ts";
+import { createTeacherTools } from "../agent/tools.ts";
 import { getChat, saveMessages } from "../store/chats.ts";
 
 /**
@@ -27,7 +28,7 @@ export async function handleChatRequest(req: Request, agent?: TeacherAgent): Pro
 	}
 
 	return createAgentUIStreamResponse({
-		agent: agent ?? createTeacherAgent(),
+		agent: agent ?? createTeacherAgent(undefined, createTeacherTools({ chatId })),
 		uiMessages: body.messages as UIMessage[],
 		onFinish: ({ messages, isAborted }) => {
 			// Persist even when aborted: the partial transcript (including any