hermes - 💡(How to fix) Fix [mcp_lazy] MEDIUM: _prev_mode dict leaks and goes stale; not cleared on session evict

Severity: MEDIUM (concurrency/correctness, leak + stale state)

Module-level _prev_mode dict leaks and goes stale; not cleared on session evict.

Evidence

• plugins/mcp_lazy/hook_impl.py:20, 141 — module-level _prev_mode keyed by session_id.
• plugins/mcp_lazy/pool.py:160 — evict() never touches _prev_mode.

The map grows unbounded (one entry per session for process lifetime) and a reused session_id retains a stale prior discovery_mode.

Impact

Unbounded memory growth on long-lived processes; stale mode applied to a reused session id after /new.

Fix

_prev_mode.pop(session_id, None) inside evict(), or move the map into the per-session DeferredToolPool so it is evicted with the pool.

Filed from opus-4.8 plugin audit (mcp_lazy).