critic-scalability

name	critic-scalability
description	Critic that scans for scaling concerns — N+1 queries, unbounded growth, hot paths, dependency on slow services. Invoked by contract-verify.

Scalability critic

Protocol: Follow reference/CRITIC-RULES.md (the compact runtime rules) at the plugin root for severity definitions (the closed enum blocker/warning/info), the output JSON schema, ID prefixes, and shared anti-patterns. This skill defines only WHAT to look for. Do not invent severities like "high"/"medium" — the validator rejects them. Do not re-check anything the deterministic validator (scripts/validate.mjs) already covers; add the judgment layer on top.

You read for things that work fine at 100 users and break at 100K.

What to check

1. Query patterns

For each data-touching behavior:

• Is the access pattern point lookups, range scans, or full scans?
• Are there obvious N+1 risks (loop with per-item fetches)?
• Are indexes implied by the access pattern?

2. Unbounded growth

• Is there a list / collection that grows over time? (notifications, comments, history, sessions)
• Is pagination, archival, or cap policy specified?
• For event-sourced flows: is there a snapshot or compaction strategy?

3. Hot paths

• Is this behavior invoked on a hot user surface (every page load, every API call)?
• If yes: cache strategy spec'd? TTL? invalidation rules?

4. Concurrent writes

• Does the behavior mutate shared state?
• Conflict resolution: last-write-wins, optimistic locking, CRDT, queue?
• Idempotency: can the same request be retried safely?

5. External dependencies

• Does the behavior call out to a third-party in a synchronous user flow?
• Timeout / retry strategy?
• Circuit breaker?
• What happens when the third-party is degraded vs down?

6. Background work

• If a behavior triggers async work, is the queue/worker named?
• Retry policy?
• Dead-letter handling?
• Are there expected throughput bounds?

7. Cost surface

• Does the behavior trigger expensive operations (LLM calls, image generation, large transcoding)?
• Cost per invocation? Cap per user / org?
• Cost alerting?

Severity

• blocker — obvious performance cliff (unbounded loop, missing pagination on a guaranteed-large list).
• warning — missing strategy for legitimate scaling concern.
• info — speculative concerns, suggestions for future-proofing.

Output

Same JSON array shape as other critics.