Widget, golden and accessibility testing

One harness pins the surface; layout and accessibility are asserted by computed geometry on the real widget tree, not by blessed pixels. Goldens are a narrow, honest safety net for glyph shaping and mirroring — never the layout gate. This skill covers the widget tier; for the pure-core / Drift / Notifier tiers see testing-strategy.

Read the reference for the task at hand:

• references/harness-and-mediaquery.md — pumpApp, Device presets, the four load-bearing lines, driving MediaQuery flags, finder policy.
• references/overflow-and-textscale.md — the two overflow classes, the three traps, the matrix, the fit assertion, and the four wrong fixes.
• references/a11y-guidelines-and-limits.md — the four built-in guidelines and their defects, the semantics/traversal gate, pure-Dart contrast, and what automation genuinely cannot cover.
• references/golden-two-lanes.md — the golden-refusal argument, the Ahem-vs-real-font lanes, RTL goldens, and blocking accidental blessing.

Run scripts/check-test-hygiene.sh before a PR.

Non-negotiable rules