Summary

loadSessionStore() in src/config/sessions/store.ts uses JSON5.parse() to read sessions.json, but the file is always written by JSON.stringify() (standard JSON). JSON5 parsing is ~35x slower than native JSON.parse for the same input.

Evidence

Write path (standard JSON)

// src/config/sessions/store.ts — saveSessionStoreUnlocked()
const json = JSON.stringify(store, null, 2);
await fs.promises.writeFile(tmp, json, { mode: 0o600, encoding: "utf-8" });

Read path (JSON5 — unnecessary)

// src/config/sessions/store.ts — loadSessionStore()
import JSON5 from "json5";
// ...
const parsed = JSON5.parse(raw);

Since JSON.stringify only produces valid standard JSON (no comments, no trailing commas, no unquoted keys), JSON5.parse provides no benefit here.

Benchmark Results

Synthetic sessions.json files with realistic session entries (~0.7 KB each), 20 iterations per size, median reported:

At 5,000 entries (3.5 MB), JSON5.parse takes ~245ms vs ~6ms for JSON.parse.

In a real-world incident, 250 sessions with large transcripts produced a 61 MB file — at that scale, JSON5.parse would take multiple seconds per read.

Real-world Impact

• loadSessionStore is called on every inbound message (cache miss path, 45s TTL)
• With a large sessions.json, every cache miss blocks the event loop for hundreds of ms or seconds
• This contributed to 30s–1min response latency in a production deployment (see Isolated sessions from cron jobs accumulate indefinitely, causing sessions.json bloat and severe performance degradation #14511)

Suggested Fix

Replace JSON5.parse with JSON.parse in loadSessionStore():

- const parsed = JSON5.parse(raw);
+ const parsed = JSON.parse(raw);

Optionally, add a JSON5.parse fallback for backwards compatibility with any hand-edited files:

let parsed;
try {
  parsed = JSON.parse(raw);
} catch {
  // Fallback for hand-edited files that may use JSON5 syntax
  parsed = JSON5.parse(raw);
}

This is a one-line change with zero risk for machine-generated files and a 35x performance improvement on the hot path.

Environment

• Node.js v22.22.0
• json5@2.x
• Linux x64 (KVM VM)