extraction cleanup: events ledger dies, markdown source view, auditor-as-linker (2026-09-27 rulings)

The graph becomes raw reasoning chains only. Quiz outcomes and
understanding observations are no longer formalized; assessment
moves to the future practice module.

Events ledger removed end-to-end: LedgerEvent/LedgerEventKind/
UnderstandingLevel/ExtractionAttribution/AuditResult.dropped and
snapshot nodeObservations deleted from contracts; quizEvent builder
and the events step of mergeFindings gone; appendEvent/readEvents
dropped from the port and store; LEDGER_FILES loses events.jsonl
with a one-time purge of a stale file next to the nodes ledger;
graph-deletion and the delete dialog lose event purge + quiz-answer
impact counts; GraphSessionProposition becomes a pure birth list.

Whole-session markdown source view: new core/session-markdown.ts is
the shared formatting engine (id-anchored speaker blocks, quiz/
recall/question blocks, tool one-liners) — the extractor's prompt
view and the future user-facing export render from one engine.
Coverage fingerprints deliberately stay on the old line format
(content-hash semantics; re-formatting never re-opens covered
history). The whole session goes to the extractor — no phase cut.

Auditor refocused as the identity linker: never sees the source;
explores the graph via new auditor-specific tools in
agent/tools/graph.ts (find — glob over name/statement/aliases;
list_sessions; list_propositions with full statement text; no
timestamps) instead of an injected full-graph dump; equivalence
bias — paraphrases merge, only genuinely distinct propositions stay
apart; no drop channel, the extractor is fully trusted; may draw
bridging edges (typed follows/supports) between existing nodes and
the batch, resolved by the merger with chat-scoped message-less
provenance. Agentic loop, maxTurns 16.

UI: the node detail card gains an edges section above the sessions
list (follows-from / supported-by / what-follows / what-it-supports,
rendered only when present, click-to-select neighbors); the
understanding-note chips are gone.

Prober list_propositions reworded to what a session covered —
names only, no levels. docs/architecture.md + README updated to
the as-built pipeline. Gates: typecheck, 1059/1059, lint, build.

src/store/graph.ts

@@ -1,5 +1,5 @@
 /**
- * GraphStore — the fs JSONL adapter: five append-only ledgers at
+ * GraphStore — the fs JSONL adapter: four append-only ledgers at
  * config.LEDGER_FILES (contracts.ts "v1 emission").
  *   nodes.jsonl     GraphNode        — one line per node write: the FIRST
  *                                      line for an id defines it; a later
@@ -10,7 +10,6 @@
  *   edges.jsonl    GraphEdge        — one line per edge ASSERTION (a second
  *                                      session asserting the same (from,to,type)
  *                                      appends another line; reads merge)
- *   events.jsonl    LedgerEvent      — quiz outcomes + understanding observations
  *   mappings.jsonl  NodeMapping      — the session→graph identity map:
  *                                      (chatId, sourceId) → graphNodeId
  *   sessions.jsonl  SessionCheckpoint— emission checkpoints (foldedAt)
@@ -34,8 +33,6 @@ import type {
 	GraphEdge,
 	GraphNode,
 	ExtractionRunUsage,
-	LedgerEvent,
-	LedgerEventKind,
 	NotesSource,
 	NodeMapping,
 	Position,
@@ -110,15 +107,6 @@ const isGraphEdge = (v: unknown): v is GraphEdge =>
 	Array.isArray(v.provenance) &&
 	v.provenance.every(isProvenancePoint);
 
-const EVENT_KINDS: readonly LedgerEventKind[] = ["correct", "miss", "dont-know", "observation"];
-
-const isLedgerEvent = (v: unknown): v is LedgerEvent =>
-	isRecord(v) &&
-	(v.nodeId === null || isString(v.nodeId)) &&
-	(EVENT_KINDS as readonly string[]).includes(v.kind as string) &&
-	isString(v.chatId) &&
-	isString(v.at);
-
 const isNodeMapping = (v: unknown): v is NodeMapping =>
 	isRecord(v) && isString(v.chatId) && isString(v.sourceId) && isString(v.graphNodeId);
 
@@ -149,13 +137,6 @@ export const graphStore: GraphStore = {
 		return readValid(LEDGER_FILES.edges, isGraphEdge);
 	},
 
-	appendEvent(event: LedgerEvent): void {
-		appendLine(LEDGER_FILES.events, event);
-	},
-	readEvents(): LedgerEvent[] {
-		return readValid(LEDGER_FILES.events, isLedgerEvent);
-	},
-
 	appendMapping(mapping: NodeMapping): void {
 		appendLine(LEDGER_FILES.mappings, mapping);
 	},
@@ -217,7 +198,6 @@ export const graphStore: GraphStore = {
 	rewriteLedgers(next: {
 		nodes?: GraphNode[];
 		edges?: GraphEdge[];
-		events?: LedgerEvent[];
 		mappings?: NodeMapping[];
 		coverage?: CoverageEntry[];
 		checkpoints?: SessionCheckpoint[];
@@ -225,7 +205,6 @@ export const graphStore: GraphStore = {
 		const files = {
 			nodes: LEDGER_FILES.nodes,
 			edges: LEDGER_FILES.edges,
-			events: LEDGER_FILES.events,
 			mappings: LEDGER_FILES.mappings,
 			coverage: LEDGER_FILES.coverage,
 			checkpoints: LEDGER_FILES.sessions,
@@ -326,5 +305,22 @@ function writeSourceMap(map: Record<string, NotesSource>): void {
 	fs.writeFileSync(SOURCES_FILE, JSON.stringify(map, null, "\t"), "utf-8");
 }
 
+// ─── one-way migration: the events ledger is gone (2026-09-27) ────────────────
+// Quiz outcomes and understanding observations are no longer formalized in
+// the graph — the pipeline writes nodes + edges only. A stale events.jsonl
+// left by an earlier build is deleted once, here, at adapter load: dead
+// ledgers are exactly the confusion the cleanup removes (owner ruling).
+{
+	const legacyEvents = path.join(path.dirname(LEDGER_FILES.nodes), "events.jsonl");
+	try {
+		if (fs.existsSync(legacyEvents)) {
+			fs.rmSync(legacyEvents);
+			console.info(`[graph-store] purged legacy events ledger: ${legacyEvents}`);
+		}
+	} catch (err) {
+		console.warn(`[graph-store] could not purge legacy events ledger:`, err);
+	}
+}
+
 const isNotesSource = (v: unknown): v is NotesSource =>
 	isRecord(v) && isString(v.id) && isString(v.filePath) && isString(v.importedAt);