v0 scaffold: teacher runtime (hermetic pi SDK), data model, ledgers, normalizer

- teacher/system-prompt.md: teach methodology + quiz/ask guidelines folded in
- extensions/: quiz.ts + ask-user-question.ts (hermetic copies)
- src/teacher/create-session.ts: isolated agent (noTools builtin, own agentDir/sessions/prompt)
- src/schema.ts + ledger.ts: append-only ledgers, known-vs-understood data model
- src/extract/normalize.ts: session JSONL -> canonical doc (verified on real session)
- extractor/merger/derive/what-next: specified stubs

config.ts

@@ -0,0 +1,24 @@
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+/** Repository root (this file is at <root>/config.ts). */
+export const ROOT = path.dirname(fileURLToPath(import.meta.url));
+
+export const PATHS = {
+	root: ROOT,
+	extensions: path.join(ROOT, "extensions"),
+	teacherPrompt: path.join(ROOT, "teacher", "system-prompt.md"),
+	data: path.join(ROOT, "data"),
+	/** Hermetic pi agentDir: settings, auth, and NOTHING from ~/.pi/agent except a symlinked auth.json. */
+	agentDir: path.join(ROOT, "data", "agent"),
+	sessions: path.join(ROOT, "data", "sessions"),
+	graph: path.join(ROOT, "data", "graph"),
+} as const;
+
+export const LEDGER_FILES = {
+	nodes: path.join(PATHS.graph, "nodes.jsonl"),
+	edges: path.join(PATHS.graph, "edges.jsonl"),
+	events: path.join(PATHS.graph, "events.jsonl"),
+	mappings: path.join(PATHS.graph, "mappings.jsonl"),
+	sessions: path.join(PATHS.graph, "sessions.jsonl"),
+} as const;