Problem

In multi-user gateway deployments (e.g., multiple Telegram users sharing one Hermes instance), user data leaks across sessions:

1. System prompt injection — USER.md shared across all users

USER.md is a single shared file (~/.hermes/memories/USER.md). When User A's profile (name, school, DOB, goals) is in USER.md, User B sees User A's identity in their system prompt.

Fix: Per-user memory directories — memories/{chat_id}/USER.md and memories/{chat_id}/MEMORY.md.

2. session_search cross-user leakage

session_search searches the entire session database without user filtering, exposing User A's conversation history to User B or cron jobs.

Fix: Added user_id parameter to search_messages() and list_sessions_rich() in hermes_state.py, threaded through session_search_tool.py.

3. Hindsight memory cross-contamination on iLink WeChat (微信)

The iLink Bot API (ilinkai.weixin.qq.com) reports the bot's own user_id as from_user_id for ALL inbound messages, regardless of who actually sent them. This means:

• All messages from different WeChat users share the same from_user_id
• Hindsight stores them in the same memory bank
• User A's memories contaminate User B's context

Fix: Per-platform retain gate in hindsight/__init__.py — skips auto_retain on platforms that can't distinguish users (detected by platform name or identical from_user_id).

Changes (5 files, +63/-25)

How to set up per-user USER.md

mkdir -p ~/.hermes/memories/{chat_id}
echo "User profile..." > ~/.hermes/memories/{chat_id}/USER.md

Testing

1. Start gateway with two Telegram users → verify User B doesn't see User A's profile
2. User B calls session_search → verify only User B's sessions appear
3. For WeChat/iLink users → verify Hindsight retains memories per contact, not globally

Related

Supersedes #12571 (original session_search + iLink fix, unmerged)