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/store/graph.ts

@@ -10,8 +10,6 @@
  *   edges.jsonl    GraphEdge        — one line per edge ASSERTION (a second
  *                                      session asserting the same (from,to,type)
  *                                      appends another line; reads merge)
- *   mappings.jsonl  NodeMapping      — the session→graph identity map:
- *                                      (chatId, sourceId) → graphNodeId
  *   sessions.jsonl  SessionCheckpoint— emission checkpoints (foldedAt)
  *
  * Plus config.SOURCES_FILE (sources.json): the imported-notes bookkeeping
@@ -34,7 +32,6 @@ import type {
 	GraphNode,
 	ExtractionRunUsage,
 	NotesSource,
-	NodeMapping,
 	Position,
 	ProvenancePoint,
 	CoverageEntry,
@@ -107,9 +104,6 @@ const isGraphEdge = (v: unknown): v is GraphEdge =>
 	Array.isArray(v.provenance) &&
 	v.provenance.every(isProvenancePoint);
 
-const isNodeMapping = (v: unknown): v is NodeMapping =>
-	isRecord(v) && isString(v.chatId) && isString(v.sourceId) && isString(v.graphNodeId);
-
 const isCheckpoint = (v: unknown): v is SessionCheckpoint =>
 	isRecord(v) && isString(v.chatId) && isString(v.foldedAt);
 
@@ -137,13 +131,6 @@ export const graphStore: GraphStore = {
 		return readValid(LEDGER_FILES.edges, isGraphEdge);
 	},
 
-	appendMapping(mapping: NodeMapping): void {
-		appendLine(LEDGER_FILES.mappings, mapping);
-	},
-	readMappings(): NodeMapping[] {
-		return readValid(LEDGER_FILES.mappings, isNodeMapping);
-	},
-
 	appendCheckpoint(checkpoint: SessionCheckpoint): void {
 		appendLine(LEDGER_FILES.sessions, checkpoint);
 	},
@@ -198,14 +185,12 @@ export const graphStore: GraphStore = {
 	rewriteLedgers(next: {
 		nodes?: GraphNode[];
 		edges?: GraphEdge[];
-		mappings?: NodeMapping[];
 		coverage?: CoverageEntry[];
 		checkpoints?: SessionCheckpoint[];
 	}): void {
 		const files = {
 			nodes: LEDGER_FILES.nodes,
 			edges: LEDGER_FILES.edges,
-			mappings: LEDGER_FILES.mappings,
 			coverage: LEDGER_FILES.coverage,
 			checkpoints: LEDGER_FILES.sessions,
 		} as const;