Avoid listing models for explicit text model IDs

[chubes4]

Summary

• Adds a provider-overridable path for explicit model IDs to provide metadata without listing all provider models first.
• Applies explicit metadata consistently across getModelMetadata(), hasModelMetadata(), and listed model metadata for matching listed IDs.
• Keeps explicit metadata request-local and memoized per directory instance instead of storing synthetic metadata in the shared models cache.

Fixes #230.

Why

Explicit provider/model selection currently calls the provider model-list endpoint before the model can be instantiated. For providers that accept explicit/current model IDs, that means getProviderModel( 'openai', 'gpt-5.4' ) can fail on a transient GET /models issue before the actual generation endpoint has a chance to validate the explicitly requested model.

Testing

• composer test -- --filter AbstractApiBasedModelMetadataDirectoryTest
• composer lint

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafting the patch, tests, and PR description; Chris reviewed the behavior on a local Studio site and remains responsible for the change.

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Co-authored-by: chubes4 <[email protected]>
Co-authored-by: JasonTheAdams <[email protected]>
Co-authored-by: felixarntz <[email protected]>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.26%. Comparing base (6317042) to head (b5b0e68).
⚠️ Report is 7 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk     #231      +/-   ##
============================================
+ Coverage     88.12%   88.26%   +0.13%     
- Complexity     1213     1225      +12     
============================================
  Files            60       61       +1     
  Lines          3934     3962      +28     
============================================
+ Hits           3467     3497      +30     
+ Misses          467      465       -2     

Flag	Coverage Δ
unit	88.26% <100.00%> (+0.13%)	⬆️

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[felixarntz]

@chubes4 While this addresses the reported concern, it creates data inconsistencies when considering the API surface of this class holistically.

I think there's a path forward, but it requires some modifications in the approach.

[chubes4]

Updated this to address the consistency concern:

• getModelMetadata() and hasModelMetadata() now check explicit metadata before the list/cache path, so provider-local metadata is authoritative when available.
• listModelMetadata() still performs the required list request, then overlays explicit metadata for matching listed model IDs so listed data and direct lookup agree for the same ID.
• Explicit metadata is memoized only for the directory instance, avoiding persistence/cache invalidation concerns for synthetic metadata.

Verified with:

• composer test -- --filter AbstractApiBasedModelMetadataDirectoryTest
• composer lint