## What happened?

For pass-through endpoints registered via `general_settings.pass_through_endpoints[]` (i.e. custom user-defined paths, not the built-in provider-specific handlers `/anthropic/v1/messages`, `/openai/v1/*`, `/vertex_ai/*`, `/gemini/*`, Cursor), every request is logged to Langfuse and `LiteLLM_SpendLogs` indistinguishably:

- `observation.model = "unknown"` — `pass_through_endpoints.py` reads `model` from request body (`_parsed_body.get("model") or "unknown"`), but many non-OpenAI providers (fal.ai, Modal, ComfyUI-style workflows, image-gen APIs) do not carry `model` in body — the model identity lives in the URL path itself. - No tag identifies the upstream endpoint anywhere in `trace.tags` or `LiteLLM_SpendLogs.request_tags`. - The full URL is captured in `PassthroughStandardLoggingPayload.url` but is not propagated to either `standard_logging_object.metadata` or `standard_logging_object.request_tags`, so downstream Langfuse / Spend Logs see nothing.

Net effect: e.g. all of `/my-fal/fal-ai/nano-banana-2/edit`, `/my-fal/fal-ai/flux/schnell`, `/my-fal/openai/gpt-image-2/edit` produce trace records that are byte-identical except for timestamp and request body — impos…