fix: raise session hygiene threshold from 50% to 85% of context

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)

gateway/run.py

@@ -1125,10 +1125,16 @@ class GatewayRunner:
                 get_model_context_length,
             )
 
-            # Read model + compression config from config.yaml — same
+            # Read model + compression config from config.yaml.
-            # source of truth the agent itself uses.
+            # NOTE: hygiene threshold is intentionally HIGHER than the agent's
+            # own compressor (0.85 vs 0.50).  Hygiene is a safety net for
+            # sessions that grew too large between turns — it fires pre-agent
+            # to prevent API failures.  The agent's own compressor handles
+            # normal context management during its tool loop with accurate
+            # real token counts.  Having hygiene at 0.50 caused premature
+            # compression on every turn in long gateway sessions.
             _hyg_model = "anthropic/claude-sonnet-4.6"
-            _hyg_threshold_pct = 0.50
+            _hyg_threshold_pct = 0.85
             _hyg_compression_enabled = True
             try:
                 _hyg_cfg_path = _hermes_home / "config.yaml"
@@ -1144,22 +1150,18 @@ class GatewayRunner:
                     elif isinstance(_model_cfg, dict):
                         _hyg_model = _model_cfg.get("default", _hyg_model)
 
-                    # Read compression settings
+                    # Read compression settings — only use enabled flag.
+                    # The threshold is intentionally separate from the agent's
+                    # compression.threshold (hygiene runs higher).
                     _comp_cfg = _hyg_data.get("compression", {})
                     if isinstance(_comp_cfg, dict):
-                        _hyg_threshold_pct = float(
-                            _comp_cfg.get("threshold", _hyg_threshold_pct)
-                        )
                         _hyg_compression_enabled = str(
                             _comp_cfg.get("enabled", True)
                         ).lower() in ("true", "1", "yes")
             except Exception:
                 pass
 
-            # Also check env overrides (same as run_agent.py)
+            # Check env override for disabling compression entirely
-            _hyg_threshold_pct = float(
-                os.getenv("CONTEXT_COMPRESSION_THRESHOLD", str(_hyg_threshold_pct))
-            )
             if os.getenv("CONTEXT_COMPRESSION_ENABLED", "").lower() in ("false", "0", "no"):
                 _hyg_compression_enabled = False