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

src/extract/merge.ts

@@ -0,0 +1,22 @@
+/**
+ * Stage 3 — Merge (deterministic code + LLM adjudication for node identity).
+ * NOT YET IMPLEMENTED. Interface specified:
+ *
+ *   Input:  ExtractedSession (Stage 2 output) + canonical graph
+ *   1. Embed canonical node statements (cached) → kNN candidates per incoming node.
+ *   2. ONE LLM adjudication call per session: each pair →
+ *        same    → alias + attach events to canonical node
+ *        related → new node + proposed cross-session edge (the quiet superpower)
+ *        unrelated → new node, no edge
+ *   3. Apply deterministically; log every decision as a SessionMapping
+ *      (reversible by design — wrong merges must be one-line fixes).
+ *
+ * Policy: fully automatic, conservative — prefer duplicates over wrong merges.
+ * No domain filter on candidates (cross-domain merging is the point).
+ */
+
+import type { ExtractedSession } from "../schema.ts";
+
+export async function mergeSession(extraction: ExtractedSession): Promise<void> {
+	throw new Error("Not implemented — Stage 3 (merger) comes after the extractor.");
+}