Fixes#21070.
This is a small cleanup around model metadata handling for
gateway/provider model names. It follows the report and proposed
direction from @dkbush by keeping the fallback metadata warning useful
without repeating it every turn, and by tightening the existing
provider-prefix lookup path.
- Track fallback metadata warning slugs in session state so each
unresolved model warns once per session.
- Keep warning emission outside the session-state lock and preserve the
existing warning text.
- Allow one-segment provider prefixes with hyphenated provider IDs,
while preserving the multi-segment rejection behavior.
- Add focused coverage for warning dedupe and hyphenated provider-prefix
metadata matching.
Testing:
- Ran `just fmt`.
- Ran `git diff --check`.
- Added tests for the new warning dedupe and provider-prefix lookup
behavior.
d5f0b6d63a