transformModelForProvider only handled github-copilot provider, leaving
google provider models untransformed. This caused ProviderModelNotFoundError
when google/gemini-3-flash was sent to the API (correct ID is
gemini-3-flash-preview).
Changes:
- Add google provider to transformModelForProvider with idempotent regex
negative lookahead to prevent double -preview suffix
- Fix category-default path in model-resolution-pipeline when
availableModels is empty but connected provider exists
- Fix getFirstFallbackModel first-run path that constructed raw model IDs
without transformation
- Fix github-copilot provider gemini transforms to also use idempotent
regex (was vulnerable to double-transform)
- Extract transformModelForProvider to shared module (single source of
truth, imported by cli and shared layers)
- Add 20 new test cases: unit tests for both providers, runtime
integration tests for category-default and fallback-chain paths,
double-transform prevention for both providers
