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/core/ports.ts

@@ -18,7 +18,6 @@ import type {
 	GraphNode,
 	JobKind,
 	JobRecord,
-	LedgerEvent,
 	ExtractionRunUsage,
 	NodeMapping,
 	PlanTree,
@@ -84,8 +83,6 @@ export interface GraphStore {
 	readEdges(): GraphEdge[];
 
 	/** Append one quiz outcome / understanding observation. */
-	appendEvent(event: LedgerEvent): void;
-	readEvents(): LedgerEvent[];
 
 	/** Append one identity-map line (chat's tree node → graph node). */
 	appendMapping(mapping: NodeMapping): void;
@@ -130,7 +127,6 @@ export interface GraphStore {
 	rewriteLedgers(next: {
 		nodes?: GraphNode[];
 		edges?: GraphEdge[];
-		events?: LedgerEvent[];
 		mappings?: NodeMapping[];
 		coverage?: CoverageEntry[];
 		checkpoints?: SessionCheckpoint[];