Users who inspect ~/.hermes/sessions/sessions.json see only gateway entries
(e.g. agent:main:whatsapp:dm:...) and mistake it for the session index that
hermes sessions list / /sessions read — which is actually state.db. Issue
#49361 reported CLI sessions as 'invisible' on this premise.
- gateway/session.py: write a self-documenting _README sentinel at the top of
sessions.json explaining it's the gateway routing index and that ALL sessions
(CLI/TUI/gateway) live in state.db; skip _-prefixed keys on load so the
sentinel never round-trips into a SessionEntry.
- Harden every sessions.json reader against the sentinel: mcp_serve loader,
gateway/mirror.py, gateway/channel_directory.py all skip _-prefixed keys.
- docs/user-guide/sessions.md: warning callout naming the exact symptom.
- tests: assert prune ignores metadata sentinels; add round-trip coverage.
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