feat: simplify evaluation schema to flat score/reasoning shape

[jsonbailey]

Summary

• Removed the metric key from the structured output schema. EvaluationSchemaBuilder.build() no longer takes an evaluationMetricKey parameter. Since there is only ever a single evaluation metric key per judge config, it does not need to be embedded in the schema sent to the LLM.
• Flattened the schema to a top-level {score, reasoning} shape. The old nested structure ({evaluations: {metricKey: {score, reasoning}}}) is replaced with a simple {score: number, reasoning: string} object. This is easier for LLMs to produce correctly and matches the Python SDK (fix: Remove evaluation metric key from schema which failed on some LLMs python-server-sdk-ai#105).
• Updated parsing in Judge.ts. _parseEvaluationResponse now reads score and reasoning directly from the top-level response data. The metric key is still sourced from the judge config's evaluationMetricKey and used to key the result — it just no longer appears in the schema or LLM response.

Test plan

• All 144 existing tests pass (yarn workspace @launchdarkly/server-sdk-ai test)
• Lint passes (yarn workspace @launchdarkly/server-sdk-ai lint)
• Test mocks updated to use new flat response shape
• _parseEvaluationResponse unit tests updated for simplified signature and data shape

🤖 Generated with Claude Code

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Note

Medium Risk
Changes the structured response contract and parsing for judge evaluations; any callers/providers still emitting the old nested evaluations shape will now fail evaluation parsing.

Overview
Simplifies judge structured-output handling by switching the expected/provider schema from nested evaluations[metricKey]{score,reasoning} to a flat top-level {score, reasoning} object, and removes the dynamic EvaluationSchemaBuilder entirely.

Judge.evaluate now always invokes the provider with the static schema and parses score/reasoning directly; failures log a more specific "Could not parse evaluation response" warning. Tests are updated to use the new response shape and to assert the new warning behavior for missing/malformed responses.

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[joker23]

only nits