`test/helpers/agent-sdk-runner.ts` wraps @anthropic-ai/claude-agent-sdk
with explicit `AgentSdkResult` types, process-level API concurrency
semaphore, and 3-shape 429 retry (thrown error, result-message error,
mid-stream SDKRateLimitEvent). Pins the local claude binary via
`pathToClaudeCodeExecutable`.
`test/fixtures/overlay-nudges.ts` holds the typed registry. Two
fixtures for the first measurement: `opus-4-7-fanout-toy` (3-file read)
and `opus-4-7-fanout-realistic` (mixed-tool audit). Strict validator
rejects duplicate ids, non-integer trials, unsafe overlay paths, non-safe
id chars, and missing overlay files at module load.
Adding a future overlay nudge eval = one fixture entry.
Garry Tan
6b85262422