Session hygiene was firing at the same threshold (50%) as the agent's
own context compressor, causing premature compression on every turn
in long gateway sessions (especially Telegram).
Hygiene is a safety net for pathologically large sessions that would
cause API failures — it should NOT be doing normal compression work.
The agent's own compressor handles that during its tool loop with
accurate real token counts from the API.
Changes:
- Default hygiene threshold: 0.50 → 0.85 (fires only when truly large)
- Hygiene threshold is now independent of compression.threshold config
(that setting controls the agent's compressor, not the pre-agent safety net)
- Removed env var override for hygiene threshold (CONTEXT_COMPRESSION_THRESHOLD
still controls the agent's own compressor)
6235fdde75