feat(core): tip about VRA when a build uses Layout review mode (PER-9502)

[prklm10]

Summary

• Emits a single warn-level tip immediately before the Finalized build log whenever any snapshot in a build had Layout review mode enabled (enableLayout, set via global config or per-snapshot).
• Why: Layout is a legacy review mode; VRA (Visual Review Agent) is the recommended replacement. This surfaces a contextual nudge at build finalization — where users already look — with minimal noise (one line, only when Layout is actually used).
• Key decisions:
  • Detection flips a per-build flag (build.layoutUsed) in the queue push handler; emission is gated in the end handler, so it logs at most once per process.
  • Covers both standard and parallel builds: each parallel shard runs core's end handler, so cli-build finalize needs no change.
  • Tip copy (renders with the [percy] prefix at normal log level):

    Tip: VRA is Percy's recommended visual review mode — more accurate and adaptable than Layout. Learn more: https://www.browserstack.com/docs/percy/ai-agents/visual-review-agent/overview.

Changes

• packages/core/src/snapshot.js — detection in push handler + guarded warn in end handler.
• packages/core/test/snapshot.test.js — 4 new specs.

Testing

• 4 new specs in snapshot.test.js, all passing:
  • logs the tip before finalizing when a snapshot has layout enabled
  • logs the tip when enableLayout is set globally in config
  • logs the tip only once when multiple snapshots have layout enabled
  • does not log the tip when no snapshot has layout enabled
• Lint clean (eslint from repo root).
• Note: the full local core suite shows pre-existing, environment-only failures unrelated to this change — install.test.js (global.__MOCK_IMPORTS__ undefined; ESM loader hook) and one api.test.js server-disabled spec (AggregateError vs ECONNREFUSED, a Node networking quirk). No snapshot/finalize/layout specs fail.

Post-Deploy Monitoring & Validation

• What to monitor/search
  • Logs: CLI build output for the new line Tip: VRA is Percy's recommended visual review mode.
• Validation checks (queries/commands)
  • npx percy snapshot with enableLayout: true (global or per-snapshot) → tip appears once just before Finalized build.
  • Same run without any Layout snapshot → tip does NOT appear.
• Expected healthy behavior
  • Exactly one tip line per build process when Layout is used; none otherwise. Build finalization behavior unchanged.
• Failure signal(s) / rollback trigger
  • Tip appearing on builds with no Layout usage, duplicate tips within a single process, or any change to Finalized build ordering → revert this commit (log-only change, safe to revert).
• Validation window & owner
  • Window: first few CLI releases / dogfood builds after merge. Owner: PR author.

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