feat(server-ai): stamp modelKey and modelVersion on AI usage events (AIC-2851)

[atornsii]

Summary

• Read modelKey and modelVersion from the AI Config variation payload (variation['model']) and expose them on ModelConfig
• Stamp modelKey (when present) and modelVersion on all LDAIConfigTracker metric event payloads, alongside existing modelName/providerName fields
• Default modelVersion to 1 when absent, matching variation version handling; exclude both fields from the resumption token
• Additive/backward compatible — older payloads without the new fields continue to work

Part of AIC-2851 / AIC-2849. Depends on backend payload work (AIC-2876) shipping modelKey/modelVersion on variations.

Test plan

• uv run pytest in packages/sdk/server-ai (229 passed)
• uv run mypy src/ldai
• uv run isort --check --atomic src/ldai
• uv run pycodestyle src/ldai
• Verify against a staging environment once AIC-2876 payload is available

Made with Cursor

[jsonbailey]

Holding based on our conversation today and we will follow up on slack before reviewing.