delete the mappings ledger — per-job in-memory resolution + notes fingerprint guard

The persisted (chatId, sourceId)→node table was a shared namespace across
independent chunk/batch jobs: each chunk's extractor mints local ids fresh
(p1..pN), so later chunks collided with earlier ones — propositions silently
skipped as 'already resolved' (coverage checkpointed anyway: permanent silent
loss) and edges resolved onto the wrong nodes (the 'everything links to
everything' mush). Owner ruling 2026-09-29: mergeFindings resolves THIS job's
ids in memory, nothing persists between jobs; cross-job identity is the
auditor's linkTo verdicts alone.

- contracts: NodeMapping dies; NotesSource.contentFp — sha256 of the text at
  the last run, the re-import guard (unchanged re-import = TRUE no-op, no
  model calls, no usage; changed text re-runs; legacy unstamped sources
  re-run once)
- merger: job-local resolution map, in-submit duplicate ids skip once,
  edges resolve extractor-local ids only
- ports/store: appendMapping/readMappings, LEDGER_FILES.mappings,
  rewriteLedgers.mappings gone (stale data/graph/mappings.jsonl just stops
  being read)
- session-clusters: birthSessionOf is provenance-only — the legacy
  mapping-line fallback for provenance-empty notes nodes dies
- deletion: no mapping rows to strip; stats lose mappingsRemoved
- replay-layout batches nodes by first provenance point
- graph.test pins the new independence semantics (re-merge re-creates;
  duplicate ids within one submit resolve once); extraction tests pin
  per-chunk merges + the fingerprint guard

src/core/layout-settle.ts

@@ -1,4 +1,4 @@
-import type { GraphEdge, GraphNode, NodeMapping, Position } from "./contracts.ts";
+import type { GraphEdge, GraphNode, Position } from "./contracts.ts";
 import { incrementalLayout } from "./layout.ts";
 import { birthSessionPartition } from "./session-clusters.ts";
 
@@ -19,7 +19,6 @@ import { birthSessionPartition } from "./session-clusters.ts";
 export function settleGraphLayout(graphStore: {
 	readNodes(): GraphNode[];
 	readEdges(): GraphEdge[];
-	readMappings(): NodeMapping[];
 	readPositions(): Record<string, Position>;
 	writePositions(positions: Record<string, Position>): void;
 }): void {
@@ -39,7 +38,7 @@ export function settleGraphLayout(graphStore: {
 	// core/session-clusters.ts, wave 7) — one cluster concept everywhere.
 	// The unique list is the deduped set the partition needs (lines may
 	// repeat an id — first defines).
-	const communities = birthSessionPartition(unique, graphStore.readMappings());
+	const communities = birthSessionPartition(unique);
 	const next = incrementalLayout(unique, edges, previous, { clusters: communities });
 	graphStore.writePositions(Object.fromEntries(next));
 }