The normalizeProviderModelCosts function was only setting { input: 0, output: 0 }
which doesn't match the full OpenCode provider cost shape that includes cache fields.
This fix:
- Preserves existing cost fields (input, output, cache.read, cache.write) if valid
- Adds missing cache: { read: 0, write: 0 } structure when not present
- Validates provider and model objects before modification to avoid poisoning
invalid provider metadata
- Updates ProviderModel type to include optional cache field
Fixes provider cost normalization to maintain cache field compatibility.
