Architectural Breakdown: We fixed the eval platform we're competing on: a TypeError that crashed thr

We Fixed the Eval Platform: The TypeError That Took Down Three Benchmark Pipelines At 3 AM, Sentry lit up with TypeError: Cannot read property 'map' of undefined . Three benchmark pipelines crashed. Not a memory leak, not a segfault, but a race condition hiding behind a TypeError, turning a high-stakes eval run into chaos. Here is how we resolved it, with no fluff. The Root Cause: Async Data Meets Blind Faith in .map() The error trace pointed to evaluator.ts:42 , where .map() assumed inputData.metrics would always exist. The junior dev tested with clean data, but in production, fetchBenchmarkData() (async) and evaluatePipeline() (sync) were racing . At 100+ RPS, metrics was often undefined . The Offending Code: const results = inputData . metrics . map ( metric => computeScore ( metric )); Why It Failed: Race Condition : inputData was fetched asynchronously, but evaluatePipeline() treated it as synchronous. OOM Risk : Unbounded .map() on 10K+ metrics could exhaust 8GB RAM. Worker Starvation : No concurrency limits led to thread pool exhaustion. The Fix: Guard Clauses, Bounded Queues, and Pragmatism Step 1: Fail Fast, Fail Loud Added zero-overhead runtime checks to reject bad data early: // eval-platform/core/evaluator.ts import { isNullOrUndefined } from ' ../utils/guards ' ; async function evaluatePipeline ( inputData : BenchmarkInput ): Promise < EvaluationResult > { if ( isNullOrUndefined ( inputData ?. metrics )) { throw new Error ( ' EVAL_400: metrics missing ' ); } // Proceed only if data is valid } Why? Stops TypeError crashes immediately. Cost: 1-2 CPU cycles. Negligible. Step 2: Chunked Processing for 8GB RAM Original code processed all metrics at once, causing OOM crashes. Fixed with 100-item chunks: const CHUNK_SIZE = 100 ; // 100 items ≈ 10MB peak memory const results : number [] = []; for ( let i = 0 ; i < inputData . metrics . length ; i += CHUNK_SIZE ) { const chunk = inputData . metrics . slice ( i , i + CHUNK_SIZE ); results . push (... chunk . map