hermes - 💡(How to fix) Fix AFK follow-up virtual turns can disappear or complete without delivery [1 pull requests]

Summary

AFK follow-up turns were configured and expected to run as gateway-native virtual turns, but the implementation was only present as local WIP and never made it into upstream/live code. During local dogfood before it disappeared, AFK virtual turns also exposed a delivery-path regression: an internal AFK response could be generated by the model but skipped by the adapter response-send path when a user message arrived mid-run.

Observed dogfood evidence

From local gateway logs/notes on 2026-05-07:

1. AFK follow-up: injecting 15m virtual turn for ...
2. inbound synthetic message begins: [Automated AFK follow-up] ...
3. model run completes and gateway logs response ready: ... response=379 chars
4. no matching platform send line appears afterward (Sending response / Telegram flush), so the user sees silence

User-facing impact: AFK work can silently complete without delivering its summary.

Root cause

Two separate gaps combine:

• The AFK scheduler/helper was local-only WIP and not wired into upstream GatewayRunner, so gateway.afk_followup can disappear after branch/update churn while config still contains gateway.afk_followup.
• BasePlatformAdapter._process_message_background suppresses any response when the interrupt event is set and a pending message exists. That is correct for normal user-originated stale responses, but wrong for internal synthetic events such as AFK follow-ups: the AFK summary should still be delivered, then the queued user message can drain afterward.

Desired behavior

• AFK follow-up is opt-in via gateway.afk_followup.enabled.
• A background watcher checks idle sessions at configured thresholds.
• It skips active/running sessions and queued sessions.
• It injects an internal MessageEvent so auth is bypassed but normal adapter delivery still happens.
• Internal AFK responses are not suppressed merely because a later user message is pending.
• Prompt is safety-scoped and does not request external/destructive actions.

Test coverage expected

• threshold scheduler chooses the first unfired threshold
• running/queued sessions are skipped
• watcher injects one internal virtual turn per threshold
• disabled config is inert
• adapter-level pending messages block AFK injection
• internal AFK responses still deliver when a pending user message exists