fix: detect context length for custom model endpoints via fuzzy matching + config override (#2051)

* fix: detect context length for custom model endpoints via fuzzy matching + config override

Custom model endpoints (non-OpenRouter, non-known-provider) were silently
falling back to 2M tokens when the model name didn't exactly match what the
endpoint's /v1/models reported. This happened because:

1. Endpoint metadata lookup used exact match only — model name mismatches
   (e.g. 'qwen3.5:9b' vs 'Qwen3.5-9B-Q4_K_M.gguf') caused a miss
2. Single-model servers (common for local inference) required exact name
   match even though only one model was loaded
3. No user escape hatch to manually set context length

Changes:
- Add fuzzy matching for endpoint model metadata: single-model servers
  use the only available model regardless of name; multi-model servers
  try substring matching in both directions
- Add model.context_length config override (highest priority) so users
  can explicitly set their model's context length in config.yaml
- Log an informative message when falling back to 2M probe, telling
  users about the config override option
- Thread config_context_length through ContextCompressor and AIAgent init

Tests: 6 new tests covering fuzzy match, single-model fallback, config
override (including zero/None edge cases).

* fix: auto-detect local model name and context length for local servers

Cherry-picked from PR #2043 by sudoingX.

- Auto-detect model name from local server's /v1/models when only one
  model is loaded (no manual model name config needed)
- Add n_ctx_train and n_ctx to context length detection keys for llama.cpp
- Query llama.cpp /props endpoint for actual allocated context (not just
  training context from GGUF metadata)
- Strip .gguf suffix from display in banner and status bar
- _auto_detect_local_model() in runtime_provider.py for CLI init

Co-authored-by: sudo <sudoingx@users.noreply.github.com>

* fix: revert accidental summary_target_tokens change + add docs for context_length config

- Revert summary_target_tokens from 2500 back to 500 (accidental change
  during patching)
- Add 'Context Length Detection' section to Custom & Self-Hosted docs
  explaining model.context_length config override

---------

Co-authored-by: Test <test@test.com>
Co-authored-by: sudo <sudoingx@users.noreply.github.com>

hermes_cli/banner.py

@@ -289,6 +289,8 @@ def build_welcome_banner(console: Console, model: str, cwd: str,
         _hero = HERMES_CADUCEUS
     left_lines = ["", _hero, ""]
     model_short = model.split("/")[-1] if "/" in model else model
+    if model_short.endswith(".gguf"):
+        model_short = model_short[:-5]
     if len(model_short) > 28:
         model_short = model_short[:25] + "..."
     ctx_str = f" [dim {dim}]·[/] [dim {dim}]{_format_context_length(context_length)} context[/]" if context_length else ""

hermes_cli/runtime_provider.py

@@ -24,11 +24,41 @@ def _normalize_custom_provider_name(value: str) -> str:
     return value.strip().lower().replace(" ", "-")
 
 
+def _auto_detect_local_model(base_url: str) -> str:
+    """Query a local server for its model name when only one model is loaded."""
+    if not base_url:
+        return ""
+    try:
+        import requests
+        url = base_url.rstrip("/")
+        if not url.endswith("/v1"):
+            url += "/v1"
+        resp = requests.get(url + "/models", timeout=5)
+        if resp.ok:
+            models = resp.json().get("data", [])
+            if len(models) == 1:
+                model_id = models[0].get("id", "")
+                if model_id:
+                    return model_id
+    except Exception:
+        pass
+    return ""
+
+
 def _get_model_config() -> Dict[str, Any]:
     config = load_config()
     model_cfg = config.get("model")
     if isinstance(model_cfg, dict):
-        return dict(model_cfg)
+        cfg = dict(model_cfg)
+        default = cfg.get("default", "").strip()
+        base_url = cfg.get("base_url", "").strip()
+        is_local = "localhost" in base_url or "127.0.0.1" in base_url
+        is_fallback = not default or default == "anthropic/claude-opus-4.6"
+        if is_local and is_fallback and base_url:
+            detected = _auto_detect_local_model(base_url)
+            if detected:
+                cfg["default"] = detected
+        return cfg
     if isinstance(model_cfg, str) and model_cfg.strip():
         return {"default": model_cfg.strip()}
     return {}