hermes - 💡(How to fix) Fix [workflow-engine] MEDIUM: workflow_run rate limit bypassable via concurrent calls (TOCTOU)

Severity: MEDIUM (correctness, rate-limit bypass / TOCTOU)

workflow_run per-session rate limit is bypassable via concurrent calls.

Evidence

plugins/workflow-engine/tools/run_workflow.py:124-137, 183-184 — the _check_rate read of _rate_buckets and the timestamp append (line 184) are separated by await engine.start_run(...). Two concurrent workflow_run calls for the same session both pass the cap before either appends. The module-global dict has no lock.

Impact

run_rate_per_session (default 5/min) is not enforced under concurrency — a session can exceed the cap by issuing parallel tool calls.

Fix

Reserve the slot before the await (append timestamp, then run; roll back on failure), or guard the check-and-append with an asyncio.Lock keyed per session.

Filed from opus-4.8 plugin audit (workflow-engine).