feat(web): wire local/custom endpoints into model assignment

The runtime resolver reads model.base_url from config and ignores the
OPENAI_BASE_URL env var, so a self-hosted endpoint could not be configured
from the GUI. Two changes enable it:

- POST /api/model/set accepts an optional base_url and persists it as
  model.base_url when provider=custom (still clearing stale base_url for
  hosted providers).
- POST /api/providers/validate now returns the model ids a custom endpoint
  advertises at /v1/models, so the GUI can auto-pick a default without
  asking the user to type a model name.

Refs desktop onboarding "Local / custom endpoint" bug.

hermes_cli/web_server.py

@@ -608,6 +608,12 @@ class ModelAssignment(BaseModel):
     provider: str
     model: str
     task: str = ""
+    # Optional OpenAI-compatible endpoint URL. Only honored for custom/local
+    # providers on the main slot — lets the GUI configure a self-hosted endpoint
+    # (vLLM, llama.cpp, Ollama, …) that needs no API key. The runtime resolver
+    # reads model.base_url from config (it ignores OPENAI_BASE_URL), so this is
+    # the path that actually wires a local endpoint into resolution.
+    base_url: str = ""
 
 
 _GATEWAY_HEALTH_URL = os.getenv("GATEWAY_HEALTH_URL")
@@ -1954,6 +1960,7 @@ async def set_model_assignment(body: ModelAssignment):
     provider = (body.provider or "").strip()
     model = (body.model or "").strip()
     task = (body.task or "").strip().lower()
+    base_url = (body.base_url or "").strip()
 
     if scope not in {"main", "auxiliary"}:
         raise HTTPException(status_code=400, detail="scope must be 'main' or 'auxiliary'")
@@ -1969,8 +1976,14 @@ async def set_model_assignment(body: ModelAssignment):
                 model_cfg = {}
             model_cfg["provider"] = provider
             model_cfg["default"] = model
-            # Clear stale base_url so the resolver picks the provider's own default.
-            if "base_url" in model_cfg and model_cfg.get("base_url"):
+            # Custom/local providers are defined by their endpoint URL, so a
+            # base_url must be persisted here — the runtime resolver reads
+            # model.base_url from config and no longer consults OPENAI_BASE_URL.
+            # For every other provider, clear any stale base_url so the
+            # resolver picks the provider's own default endpoint.
+            if provider.strip().lower() == "custom" and base_url:
+                model_cfg["base_url"] = base_url
+            elif "base_url" in model_cfg and model_cfg.get("base_url"):
                 model_cfg["base_url"] = ""
             # Also clear hardcoded context_length override — new model may have
             # a different context window.
@@ -2013,6 +2026,7 @@ async def set_model_assignment(body: ModelAssignment):
                 "scope": "main",
                 "provider": provider,
                 "model": model,
+                "base_url": model_cfg.get("base_url", ""),
                 "gateway_tools": gateway_tools,
             }
 
@@ -2181,6 +2195,33 @@ _CREDENTIAL_PROBES: dict[str, tuple[str, str]] = {
 }
 
 
+def _parse_model_ids(resp: "Any") -> List[str]:
+    """Extract model ids from an OpenAI-compatible ``/v1/models`` response.
+
+    Tolerant of the common shapes: ``{"data": [{"id": ...}]}`` (OpenAI / vLLM /
+    llama.cpp) and a bare ``{"data": ["id", ...]}``. Returns ``[]`` on any
+    parse/HTTP error so a slightly non-standard endpoint never hard-blocks.
+    """
+    try:
+        if not resp.is_success:
+            return []
+        payload = resp.json()
+    except Exception:
+        return []
+    data = payload.get("data") if isinstance(payload, dict) else payload
+    if not isinstance(data, list):
+        return []
+    ids: List[str] = []
+    for item in data:
+        if isinstance(item, dict):
+            mid = str(item.get("id") or "").strip()
+        else:
+            mid = str(item or "").strip()
+        if mid:
+            ids.append(mid)
+    return ids
+
+
 @app.post("/api/providers/validate")
 async def validate_provider_credential(body: EnvVarUpdate, request: Request):
     """Live-probe a provider credential before it's saved.
@@ -2199,13 +2240,15 @@ async def validate_provider_credential(body: EnvVarUpdate, request: Request):
         return {"ok": False, "reachable": True, "message": "Enter a value first."}
 
     # Local / custom endpoint: validate connectivity, not auth — any HTTP
-    # response (even 401) proves the endpoint is up.
+    # response (even 401) proves the endpoint is up. Also surface the model
+    # ids the endpoint advertises (OpenAI ``/v1/models`` shape) so the GUI can
+    # auto-pick a default without asking the user to type a model name.
     if key == "OPENAI_BASE_URL":
         url = value.rstrip("/") + "/models"
         try:
             with httpx.Client(timeout=httpx.Timeout(8.0)) as client:
-                client.get(url)
-            return {"ok": True, "reachable": True, "message": ""}
+                resp = client.get(url)
+            return {"ok": True, "reachable": True, "message": "", "models": _parse_model_ids(resp)}
         except Exception:
             return {"ok": False, "reachable": False, "message": f"Could not reach {url}."}