run eval: --evaluator-arn naming is misleading and Builtin evaluators fail without a project

[jariy17]

Problem 1: --evaluator-arn accepts non-ARN values

The --evaluator-arn flag accepts both actual ARNs and managed evaluator IDs like Builtin.Correctness. The flag name implies it only takes ARNs, which is confusing for users.

# "Builtin.Correctness" is not an ARN, but --evaluator-arn accepts it
agentcore run eval \
  --runtime-arn arn:aws:bedrock-agentcore:us-west-2:123456:runtime/my-agent \
  --evaluator-arn "Builtin.Correctness"

Problem 2: Users without a project can't use Builtin evaluators via --evaluator

Users who don't have a CLI project (e.g. running evals against a runtime ARN directly) can't use --evaluator "Builtin.Correctness" — it fails with:

No agentcore project found.
Run agentcore create to fix this.

This is because the project requirement is only skipped when both --runtime-arn and --evaluator-arn are provided:

const isArnMode = !!(cliOptions.runtimeArn && cliOptions.evaluatorArn);

Users have to know to use --evaluator-arn instead of --evaluator for Builtin evaluators when outside a project — but nothing tells them this.

Suggestion

• Rename --evaluator-arn to --evaluator-id to reflect that it accepts both ARNs and managed IDs
• Only require --runtime-arn to skip the project check, so --evaluator works with Builtin evaluators outside a project