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/contracts/graph.ts

@@ -58,6 +58,12 @@ export interface NotesSource {
 	filePath: string;
 	/** ISO — when this file was imported (the checkpoint's foldedAt). */
 	importedAt: string;
+	/** sha256 of the imported text at the last EXTRACTION run — the
+	 *  same-path re-import guard (owner, 2026-09-29): a matching
+	 *  fingerprint is a TRUE no-op (no model calls, no usage record);
+	 *  a mismatch or a legacy missing stamp re-runs the whole file.
+	 *  The mappings ledger used to give this idempotency by accident. */
+	contentFp?: string;
 	/** The run's usage log — same append-only discipline as
 	 *  ChatRecord.extractions, idempotent per startedAt. */
 	extractions?: ExtractionRunUsage[];
@@ -109,18 +115,6 @@ export interface GraphEdge {
 	provenance: ProvenancePoint[];
 }
 
-/** mappings.jsonl line — the session→graph identity map: the extraction
- *  pipeline's proposition (identified by its run-local source id) → the
- *  graph node it resolved to (created or linked). The audit trail of the
- *  auditor's identity verdicts; also the chat-scoped resolution table the
- *  merger uses to point events and edges at node ids. */
-export interface NodeMapping {
-	chatId: string;
-	/** The extractor's run-local proposition id ("p1", …). */
-	sourceId: string;
-	graphNodeId: string;
-}
-
 /** sessions.jsonl line — the emission checkpoint for one chat (which chats
  *  have been folded, and through which updatedAt — never fold twice). */
 export interface SessionCheckpoint {