Coding (Platform)

Fastify: Plan cache invalidation for metrics hook cache lifecycle

A production request path returns inconsistent decisions during retries and concurrent updates. The affected area is metrics hook.

Repair the metrics hook cache lifecycle implementation so it separates purge, refresh, and escalation actions by staleness and risk.

Evidence

Affected surface: Fastify / metrics hook.
Observed failure family: plan cache invalidation.
Scope policy: zoneState must equal healthy.

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.