fix: idle shutdown now checks session-store.db mtime

Active copilot conversations write to session-store.db even when
no vector-memory tools are called. The idle check now stats the
session store file — if its mtime is newer than lastActivity, it
counts as activity and prevents premature shutdown.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: BrainSlugs83

vector-memory-server.js

@@ -3,7 +3,7 @@ import * as sqliteVec from "sqlite-vec";
 import { Worker } from "worker_threads";
 import { join, dirname } from "path";
 import { homedir } from "os";
-import { existsSync, writeFileSync, unlinkSync, readFileSync } from "fs";
+import { existsSync, writeFileSync, unlinkSync, readFileSync, statSync } from "fs";
 import { fileURLToPath } from "url";
 import { createServer, request as httpReq } from "http";
 import { execSync } from "child_process";
@@ -341,6 +341,11 @@ setInterval(backgroundIndex, INDEX_INTERVAL_MS);
 // --- Idle shutdown ---
 if (IDLE_TIMEOUT_MS > 0) {
   setInterval(() => {
+    // If session-store.db was recently modified, count as activity
+    try {
+      const mtime = statSync(SESSION_STORE_PATH).mtimeMs;
+      if (mtime > lastActivity) lastActivity = mtime;
+    } catch {}
     const idle = Date.now() - lastActivity;
     if (idle >= IDLE_TIMEOUT_MS) {
       process.stderr.write(`[vector-memory] Idle for ${Math.round(idle / 1000)}s — shutting down.\n`);