schema stamps: lazy v1 for chats + the graph family, honest refusal

Chat records gain version (CURRENT_CHAT_VERSION), stamped by a single
writeChat choke point in the store; absence reads as v1 — existing files
migrate on their next write, no mass rewrite. The graph family (four JSONL
ledgers, sources.json, render-settings.json) shares one lazy sidecar,
graph/format.json; positions stays unstamped (rebuildable) and jobs stay
unstamped (transient).

Downgrade scenario ruled honest-refusal: records stamped newer than the
running build read as absent (chats, logged) or throw (graph family) — a
read-modify-write store never rewrites what it doesn't understand.

Golden fixtures stay the unstamped legacy shape on purpose (lazy v1 is
current-valid by design); the stamped write path is pinned by
tests/schema-stamps.test.ts. Reads never write — the golden byte-identical
pin holds.

src/core/contracts/chat.ts

@@ -52,8 +52,17 @@ export interface ChatRecord {
 	extractions?: ExtractionRunUsage[];
 	/** Per-chat model/thinking overrides for the conversation agents. */
 	settings?: ChatSettings;
+	/** SCHEMA STAMP (schema-versioning wave, owner 2026-10-10): LAZY v1 —
+	 *  existing records stay unstamped (absence reads as v1); every write
+	 *  stamps the current version. A record stamped NEWER than this build
+	 *  (the downgrade scenario) is REFUSED on read: a read-modify-write
+	 *  store must never rewrite what it doesn't understand. */
+	version?: number;
 }
 
+/** The chat record format this build writes and understands. */
+export const CURRENT_CHAT_VERSION = 1;
+
 /** The conversation agents' runtime model choice (model-control wave,
  *  2026-09-12): a per-chat override of config.ts's pinned prober/teacher
  *  spec. Absent fields fall back to config; written by the model picker

src/core/contracts/graph.ts

@@ -120,6 +120,10 @@ export interface NamingRunStats {
 	appended: number;
 }
 
+/** The graph-family format version this build writes and understands
+ *  (the format.json sidecar — src/store/graph-format.ts). */
+export const CURRENT_GRAPH_FORMAT_VERSION = 1;
+
 
 export interface GraphNode {
 	/** Opaque stable id, store-assigned: "n_" + nanoid-like. */