Change model display format from "model (provider)" to "model__provider"

[BillJr99]

Summary

This PR changes the model ID display format returned by GET /v1/models from "model (provider)" to "model__provider" to improve compatibility with strict client validators and prevent silent truncation in client menus.

Key Changes

• New display format: Model IDs now use double-underscore separator (model__provider) instead of space and parentheses (model (provider))

  • Eliminates spaces and parentheses that break strict validators (e.g., Hermes)
  • Avoids silent truncation at / boundaries in some clients
  • Sanitizes spaces in upstream model IDs and provider names to underscores

• Backward compatibility: The resolver still accepts the legacy "model (provider)" format for existing clients

  • Cold-cache fallback parsing added for both new and legacy formats
  • Clients can submit any of three forms: new model__provider, canonical provider/model, or legacy model (provider)

• Documentation updates:

  • README now documents the new display format and explains why it was chosen
  • Docstrings updated to reflect format changes and backward compatibility
  • Test client validation updated to recognize all three accepted formats

• Comprehensive test coverage: New test file test_proxy_display_id_format.py ensures:

  • Display IDs follow the model__provider format with no spaces/parens
  • Spaces in upstream model names and provider names are sanitized to underscores
  • Original upstream IDs are preserved for routing
  • Legacy format still resolves correctly for backward compatibility

Implementation Details

• The _fetch_provider_models() function now sanitizes both the upstream model ID and provider name before constructing the display ID
• The _resolve_provider() function includes cold-cache fallback parsing for the new __ separator format
• Route cache continues to use the sanitized display ID as the key, while the original upstream ID is preserved in _upstream_id for actual request forwarding

https://claude.ai/code/session_018vws2p6bhd3xESL3Jx4S3h