fix(llm): normalize OpenAI-compatible chat URLs

Normalize OpenAI-compatible chat URL shapes so base /v1 endpoints route to /v1/chat/completions while already-full chat endpoints remain idempotent.

Preserve native local Ollama routing for bare localhost:11434 endpoints, keep localhost:11434/v1 as OpenAI-compatible, and add focused regression coverage for provider detection, chat target URLs, and model listing from /v1.

Part of #541.

src/llm_core.py

@@ -345,6 +345,18 @@ def _normalize_ollama_url(url: str) -> str:
     return base.rstrip("/") + "/chat"
 
 
+def _normalize_openai_chat_url(url: str) -> str:
+    """Ensure an OpenAI-compatible base URL points at /chat/completions."""
+    base = (url or "").strip().rstrip("/")
+    if not base:
+        return base
+    if base.endswith("/chat/completions") or base.endswith("/completions"):
+        return base
+    if base.endswith("/models"):
+        base = base[: -len("/models")].rstrip("/")
+    return base + "/chat/completions"
+
+
 def _ollama_normalize_messages(messages: List[Dict]) -> List[Dict]:
     """Adapt Odysseus' canonical OpenAI-style messages to native Ollama /api/chat.
 
@@ -1563,7 +1575,7 @@ def llm_call(url: str, model: str, messages: List[Dict], temperature: float = LL
             stream=False, num_ctx=get_context_length(url, model),
         )
     else:
-        target_url = url
+        target_url = _normalize_openai_chat_url(url)
         if provider == "copilot":
             from src.copilot import apply_request_headers
             apply_request_headers(h, messages_copy)
@@ -1767,7 +1779,7 @@ async def llm_call_async(
             stream=False, num_ctx=get_context_length(url, model),
         )
     else:
-        target_url = url
+        target_url = _normalize_openai_chat_url(url)
         h = _provider_headers(provider, headers)
         if provider == "copilot":
             from src.copilot import apply_request_headers
@@ -1889,7 +1901,7 @@ async def stream_llm(url: str, model: str, messages: List[Dict], temperature: fl
         h = _provider_headers(provider, headers)
         payload = _build_chatgpt_responses_payload(model, messages_copy, temperature, max_tokens, stream=True)
     else:
-        target_url = url
+        target_url = _normalize_openai_chat_url(url)
         payload = {
             "model": model,
             "messages": messages_copy,