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/agent/tools/jobs.ts

@@ -0,0 +1,13 @@
+import type { ToolSet } from "ai";
+import type { TeacherToolContext } from "../tools.ts";
+
+/**
+ * Async sub-agent job tools — W2 workstream (research; W6 adds demo + visual).
+ * CLIENT-SIDE semantics (no execute): the turn ends with the part pending, a
+ * background runner fulfills it, and the client continuation resumes the
+ * teacher. See src/core/contracts.ts "THE ASYNC PROTOCOL" — read it first.
+ */
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+export function jobTools(ctx: TeacherToolContext): ToolSet {
+	return {};
+}