Sleeping rooms stay asleep across a restart

Idle rooms already went back to their ledgers, but a boot replayed
every ledger before the first sweep could put them to bed again — most
of a restart's fifteen seconds spent rebuilding games nobody was at.
A room put to sleep now leaves a stub beside the ledgers, with the
ledger's size at that moment; at boot a stub whose size still matches
answers for the room and the ledger stays unreplayed. Replayed rooms
take their eviction clock from the ledger's last line, so the first
sweep after a boot writes the stubs for everything long idle.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jm2auWk6RP71CjaAb4FMoG

packages/server/src/store.ts

@@ -3,7 +3,7 @@
 // command. Because the engine is deterministic, replaying a file rebuilds
 // the exact game state — server restarts lose nothing.
 
-import { appendFileSync, existsSync, mkdirSync, readdirSync, readFileSync, renameSync } from "node:fs";
+import { appendFileSync, existsSync, mkdirSync, readdirSync, readFileSync, renameSync, statSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
 
 export interface RoomMetaLine {
@@ -128,24 +128,48 @@ export function countRoomFiles(): number {
   return readdirSync(DATA_DIR).filter((f) => f.endsWith(".jsonl")).length;
 }
 
-/** Read every persisted room's lines, keyed by room id. */
-export function readAllRooms(): Map<string, RoomLine[]> {
+/** Every room with a ledger on disk. */
+export function listRoomIds(): string[] {
   ensureDataDir();
-  const rooms = new Map<string, RoomLine[]>();
-  for (const file of readdirSync(DATA_DIR)) {
-    if (!file.endsWith(".jsonl")) continue;
-    const id = file.slice(0, -".jsonl".length);
-    try {
-      const lines = readFileSync(join(DATA_DIR, file), "utf8")
-        .split("\n")
-        .filter((l) => l.trim().length > 0)
-        .map((l) => JSON.parse(l) as RoomLine);
-      if (lines.length > 0 && lines[0]!.kind === "meta") rooms.set(id, lines);
-    } catch (e) {
-      console.error(`skipping unreadable room file ${file}:`, e);
-    }
+  return readdirSync(DATA_DIR).filter((f) => f.endsWith(".jsonl")).map((f) => f.slice(0, -".jsonl".length));
+}
+
+/** A ledger's size and the moment of its last line. */
+export function ledgerStat(roomId: string): { bytes: number; mtimeMs: number } | null {
+  if (!safeRoomId(roomId)) return null;
+  const file = fileFor(roomId);
+  if (!existsSync(file)) return null;
+  const st = statSync(file);
+  return { bytes: st.size, mtimeMs: st.mtimeMs };
+}
+
+// --- Stubs of sleeping rooms. ---------------------------------------------
+// A room put to sleep leaves a stub beside the ledgers: what the games
+// ledger needs to answer for it, and the ledger's size at that moment. A
+// ledger only ever grows, so at boot a stub whose size still matches is
+// the room's whole truth and the room stays asleep, unreplayed.
+
+const stubDir = () => join(DATA_DIR, "..", "stubs");
+const stubFor = (roomId: string) => join(stubDir(), `${roomId}.json`);
+
+export function readStubFile<T>(roomId: string): { bytes: number; stub: T } | null {
+  if (!safeRoomId(roomId)) return null;
+  const file = stubFor(roomId);
+  if (!existsSync(file)) return null;
+  try {
+    const parsed = JSON.parse(readFileSync(file, "utf8")) as { bytes: number; stub: T };
+    return typeof parsed.bytes === "number" && parsed.stub ? parsed : null;
+  } catch (e) {
+    console.error(`unreadable stub file ${roomId}:`, e);
+    return null;
   }
-  return rooms;
+}
+
+export function writeStubFile(roomId: string, bytes: number, stub: unknown): void {
+  const file = stubFor(roomId);
+  mkdirSync(stubDir(), { recursive: true });
+  writeFileSync(file + ".tmp", JSON.stringify({ bytes, stub }), "utf8");
+  renameSync(file + ".tmp", file);
 }
 
 /** Player surprise reports and the wizards' replies share one JSONL file