feat(compression): raise compaction trigger to 85% for gpt-5.5 on Codex OAuth (#40957)

The ChatGPT Codex OAuth backend hard-caps gpt-5.5 at a 272K context window
(verified live: a ~330K-token request to chatgpt.com/backend-api/codex/responses
is rejected with context_length_exceeded while ~250K succeeds; the same slug
exposes 1.05M on the direct OpenAI API / OpenRouter and 400K on Copilot). At the
default 50% trigger, auto-compaction fires at ~136K — half the usable window.

Raise the trigger to 85% (~231K) on this exact route only, gated by a new
compression.codex_gpt55_autoraise config flag (default true). When it fires,
emit a one-time notice (CLI inline print + gateway status_callback replay) with
the exact opt-back-out command. gpt-5.5 on any other provider keeps the user's
global threshold.

- _is_codex_gpt55() matches the 5.5 family only on provider=openai-codex
- _compression_threshold_for_model() now provider-aware + opt-out param
- config key + _config_version bump (27->28) for backfill
- docs + tests (40 cases in test_arcee_trinity_overrides.py)

website/docs/developer-guide/context-compression-and-caching.md

@@ -84,6 +84,7 @@ compression:
   threshold: 0.50            # Fraction of context window (default: 0.50 = 50%)
   target_ratio: 0.20         # How much of threshold to keep as tail (default: 0.20)
   protect_last_n: 20         # Minimum protected tail messages (default: 20)
+  codex_gpt55_autoraise: true  # gpt-5.5 on Codex OAuth: raise trigger to 85% (default: true)
 
 # Summarization model/provider configured under auxiliary:
 auxiliary:
@@ -101,6 +102,22 @@ auxiliary:
 | `target_ratio` | `0.20` | 0.10-0.80 | Controls tail protection token budget: `threshold_tokens × target_ratio` |
 | `protect_last_n` | `20` | ≥1 | Minimum number of recent messages always preserved |
 | `protect_first_n` | `3` | (hardcoded) | System prompt + first exchange always preserved |
+| `codex_gpt55_autoraise` | `true` | bool | Raise the trigger to 85% for gpt-5.5 on the ChatGPT Codex OAuth route (see below). Set `false` to keep the global `threshold` |
+
+### Codex gpt-5.5 threshold autoraise
+
+The ChatGPT Codex OAuth backend hard-caps gpt-5.5 at a **272K** context window
+(the same slug exposes 1.05M on OpenAI's direct API and OpenRouter, and 400K on
+GitHub Copilot). At the default 50% trigger, compaction would fire at ~136K —
+half the window the model can actually use. When the active route is Codex
+OAuth (`provider: openai-codex`) and the model is gpt-5.5, Hermes raises the
+trigger to **85%** (~231K) and prints a one-time notice with the opt-out
+command. Only this exact route is affected; gpt-5.5 on any other provider keeps
+your global `threshold`. To opt back down to the global value:
+
+```bash
+hermes config set compression.codex_gpt55_autoraise false
+```
 
 ### Computed Values (for a 200K context model at defaults)