Clusters phases B+C: labeling records, the naming call, snapshot payload

Core-survival labelings (vision section 1, DECIDED 2026-09-13):
ClusterLabeling records in a new append-only ledger
(data/graph/cluster-labels.jsonl), immutable, id = clu_ + sha256 of the
sorted core so re-naming races and re-runs dedupe at the store seam.
matchClusterLabelings (core/clusters.ts, pure): a community keeps a
record's label while at least half its core survives in it; both sides
single-successor (a split keeps one name; greedy by overlap, ties to
the newer record).

The namer (src/agent/subagents/cluster-namer.ts): ONE singular cheap LLM
call (new 'labeler' role, glm-flash/low) names every new/changed
community at once, given member names + statements (capped at 12
members per cluster). refreshClusterLabels runs POST-EXTRACTION
(user-decided) from both front doors, fire-and-forget — naming failure
never fails the run; refreshes serialize behind a chain so parallel
imports never mint duplicate labels. import-notes.ts awaits
clusterNamingSettled before exit.

Payload: GraphSnapshot.clusters (>= MIN_CLUSTER_SIZE 3) joins detection
with labelings at read time — claimed clusters carry the record's label
and id; unlabeled ones carry a member-hash id and null label. Detection
is deterministic so no memo in v1 (ms at current scale; revisit at
vault scale).

Tests (372/372): matcher half-rule/split/merge/greedy/tie cases; naming
end-to-end through importNotes (one call, one record, claim on
re-refresh), naming failure non-fatal; snapshot derivation with
labeling join; 11 test pipelines now pin an explicit labeler seam.

src/store/graph.ts

@@ -31,6 +31,7 @@ import * as fs from "node:fs";
 import * as path from "node:path";
 import { LEDGER_FILES, SOURCES_FILE } from "../../config.ts";
 import type {
+	ClusterLabeling,
 	GraphEdge,
 	GraphNode,
 	ExtractionRunUsage,
@@ -86,6 +87,14 @@ function readValid<T>(file: string, isValid: (v: unknown) => v is T): T[] {
 const isProvenancePoint = (v: unknown): v is ProvenancePoint =>
 	isRecord(v) && isString(v.chatId) && isString(v.messageId);
 
+const isClusterLabeling = (v: unknown): v is ClusterLabeling =>
+	isRecord(v) &&
+	isString(v.id) &&
+	isString(v.label) &&
+	Array.isArray(v.core) &&
+	v.core.every(isString) &&
+	isString(v.createdAt);
+
 const isGraphNode = (v: unknown): v is GraphNode =>
 	isRecord(v) &&
 	isString(v.id) &&
@@ -164,6 +173,18 @@ export const graphStore: GraphStore = {
 		return readValid(LEDGER_FILES.sessions, isCheckpoint);
 	},
 
+	// ── cluster labelings (config.LEDGER_FILES.clusterLabels) ──
+
+	/** Idempotent by id: the id is a hash of the sorted core, so re-appending
+	 *  the same member set (re-naming races, idempotent re-runs) is a no-op. */
+	appendClusterLabel(labeling: ClusterLabeling): void {
+		if (this.readClusterLabels().some((l) => l.id === labeling.id)) return;
+		appendLine(LEDGER_FILES.clusterLabels, labeling);
+	},
+	readClusterLabels(): ClusterLabeling[] {
+		return readValid(LEDGER_FILES.clusterLabels, isClusterLabeling);
+	},
+
 	// ── imported-notes bookkeeping (config.SOURCES_FILE — a JSON map) ──
 
 	/** Upsert: keeps the existing record's usage log when re-importing. */