fix: DB backup on schema change, MCP child cleanup, codex models, usage providers OOM

- Backup DB only on real SCHEMA_VERSION change, not every app version bump
- Kill idle MCP stdio bridge children to prevent orphan process leaks
- Add getDistinctProviders to avoid loading every row JSON blob (OOM fix)
- Update codex model list (gpt-5.6 sol/terra/luna, drop 5.3 codex variants)
- Reorder Claude default models (fable first)

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lib/db/backup.js

@@ -1,9 +1,20 @@
+// DB safety backups — taken ONLY before a schema change (see migrate.js).
+//
+// ⚠️ AGENT/DEV NOTES:
+// - Backups are a best-effort safety net before schema migrations. There is NO
+//   automated restore path; recovery is manual (copy a backup file back).
+// - Backups intentionally EXCLUDE the `requestDetails` table (observability log,
+//   auto-pruned, non-critical) so a multi-hundred-MB DB backs up as a few MB.
+// - Only the newest KEEP_BACKUPS are kept; older ones are pruned automatically.
 import fs from "node:fs";
 import path from "node:path";
 import { BACKUPS_DIR, ensureDirs } from "./paths.js";
 import { timestampSlug, getAppVersion } from "./version.js";
 
-const KEEP_BACKUPS = 5;
+const KEEP_BACKUPS = 3;
+
+// Tables excluded from safety backups (large, non-critical, reproducible).
+const BACKUP_EXCLUDE_TABLES = ["requestDetails"];
 
 export function makeBackupDir(label) {
   ensureDirs();
@@ -22,6 +33,35 @@ export function backupFile(srcPath, destDir, destName = null) {
   return dest;
 }
 
+// Lightweight DB backup via ATTACH: create an empty sqlite file, copy every
+// table EXCEPT the excluded ones into it. Avoids duplicating the huge
+// observability log, so the backup stays small regardless of DB size.
+export function backupDbLite(adapter, destDir, destName = "data.sqlite") {
+  const dest = path.join(destDir, destName);
+  try { fs.rmSync(dest, { force: true }); } catch {}
+  const escaped = dest.replace(/'/g, "''");
+
+  adapter.exec(`ATTACH DATABASE '${escaped}' AS bak`);
+  try {
+    const excluded = new Set(BACKUP_EXCLUDE_TABLES);
+    const tables = adapter
+      .all(`SELECT name, sql FROM main.sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%'`)
+      .filter((t) => !excluded.has(t.name));
+
+    adapter.transaction(() => {
+      for (const t of tables) {
+        // Recreate table structure in backup DB, then copy rows.
+        const createSql = t.sql.replace(/CREATE TABLE\s+/i, "CREATE TABLE bak.");
+        adapter.exec(createSql);
+        adapter.exec(`INSERT INTO bak.${t.name} SELECT * FROM main.${t.name}`);
+      }
+    });
+  } finally {
+    try { adapter.exec("DETACH DATABASE bak"); } catch {}
+  }
+  return dest;
+}
+
 export function pruneOldBackups() {
   if (!fs.existsSync(BACKUPS_DIR)) return;
   const entries = fs.readdirSync(BACKUPS_DIR, { withFileTypes: true })