Coding (Platform)

Fastify: Compute rolling metrics for stream handler performance telemetry

An operational alert points to a contract bug that appears only under mixed production data. The affected area is stream handler.

Repair the stream handler performance telemetry implementation so it computes a fixed-width rolling average in event order.

Evidence

Affected surface: Fastify / stream handler.
Observed failure family: compute rolling metrics.
Scope policy: cohort must equal stable.

What this task practices

This coding (platform) exercise trains the same sequence expected in an interview: understand the prompt, make assumptions explicit, produce a concrete answer, and explain the decisions behind it. The task is marked medium difficulty. The private workspace adds the tools required by this round, such as recording, code execution, diagrams, evidence panels, or structured notes. It also preserves the attempt so later feedback can be compared with previous work. Evaluation is based on task-specific criteria and the candidate seniority selected in the preparation path. Public pages never expose the reference solution, hidden tests, evaluator instructions, or another candidate’s work.