Audit authored font-size basis before SVG text shaping

[softmarshmallow]

Why this exists

The stroke-width checklist rung (#80) found three authored-value mechanisms that can hide or poison a font-relative basis: basis-less relative units, var() indirection, and CSS escapes. Its patrol is deliberately stroke-scoped. The same mechanisms may reach the SVG text estate through computed font-size and therefore affect glyph metrics, but that possibility has not been measured or closed.

This issue preserves that open thread without making the dasharray or context-paint rungs own text conformance.

Current boundary

• websem reads the computed font-size for <text> and passes its used px value into text resolution.
• The The stroke-width rung: the twins' grammar celled, five silent spellings made refusals #80 font-size poison checks run only when resolving a font-relative stroke-width; absent such a width, they do not guard text shaping.
• There is no text-specific refusal fixture, refusal-register row, or contract test for these three mechanisms.
• This is a suspected silent-divergence class, not a measured defect yet. Records must not claim more until Chromium and the engine have been compared.

Required rung shape

1. Probe Chromium and websem → rframe → n0 for authored font-size through the presentation attribute, inline style, and stylesheet ingresses.
2. Cover at least basis-less relative units, var() indirection, and CSS escapes, with discriminating glyph-metric rasters rather than saturated or coincidental images.
3. For every measured silent divergence, either supply the correct basis/resolution or convert the entire spelling class into a named, registered, guarded refusal in both admissions.
4. Add committed Chromium-gated cells for admitted behavior and update the text statement of record precisely; mark probe-only findings as measured, not celled.
5. Tick no font-size or related checklist row unless its full listed grammar meets the checklist bar.

Non-goals

• Do not fold this into stroke-dasharray merely because dashes also consume lengths.
• Do not change the text join or broaden rframe's text vocabulary.