fix: align Anthropic endpoints for Claude Code compatibility

Add /v1/messages/count_tokens and switch /v1/models to Anthropic-style key auth so Claude Code probes succeed consistently.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/main.py

@@ -149,6 +149,10 @@ def auth_guard(request: Request):
     require_bearer(request, settings.api_keys)
 
 
+def anthropic_auth_guard(request: Request):
+    require_anthropic_key(request, settings.api_keys)
+
+
 def metrics_auth_guard(request: Request):
     require_metrics_access(
         request,
@@ -314,7 +318,7 @@ def _last_user_text(messages: list[dict]) -> str:
     return ""
 
 
-@app.get("/v1/models", dependencies=[Depends(auth_guard)])
+@app.get("/v1/models", dependencies=[Depends(anthropic_auth_guard)])
 async def v1_models():
     p = _require_pool()
     inst = p.pick()
@@ -642,6 +646,22 @@ def _anthropic_stop_reason(completion_tokens: int, max_tokens: int) -> str:
     return "end_turn"
 
 
+@app.post("/v1/messages/count_tokens")
+async def v1_messages_count_tokens(req: AnthropicMessagesRequest, request: Request):
+    """Anthropic-compatible token counting endpoint.
+
+    Claude Code may probe this endpoint; return Anthropic-shaped response.
+    """
+    try:
+        require_anthropic_key(request, settings.api_keys)
+    except AnthropicAuthError as exc:
+        return _anthropic_error(exc.status_code, exc.error_type, exc.message)
+
+    messages_dump = anthropic_to_internal_messages(req)
+    prompt = _messages_to_prompt(messages_dump)
+    return JSONResponse(content={"input_tokens": estimate_tokens(prompt)})
+
+
 @app.post("/v1/messages")
 async def v1_messages(req: AnthropicMessagesRequest, request: Request):
     """Anthropic Messages API compatible endpoint.