WM-0: writing-mode accepted as horizontal-tb only; vertical values refused

[thejackshelton]

What changed

• writing-mode, text-orientation and text-combine-upright are surrogate shorthands with no longhands.
  • writing-mode accepts horizontal-tb and the SVG 1.1 lr, lr-tb, rl and rl-tb, which Chrome 145 computes to horizontal-tb.
  • Every vertical value (vertical-, sideways-, tb, tb-rl) is refused with DRAGON_UNSUPPORTED_VALUE.
  • text-orientation and text-combine-upright are accepted as inert. text-combine-upright digits is refused, because Chrome 145 does not parse it.
• A var() value on writing-mode or text-combine-upright is refused. A property with no longhands is never checked after var() substitution, so --wm: vertical-rl; writing-mode: var(--wm) used to compile silently. Four tests cover it and fail without the fix.
• Keywords are lowercased ASCII-only and escapes are decoded, as elsewhere in Dragon.
• The grammar gains the SVG 1.1 writing-mode values (css-writing-modes-4 Appendix B).
• The writing-mode fixture group adds 2 layout fixtures (ltr and rtl) and 5 reject fixtures, and compares writing-mode's computed value in both renderings. The family is registered before grid, the order master's comments already expect.

Test changes, with reasons

• logical-props reject-writing-mode and logical.test.ts now expect DRAGON_UNSUPPORTED_VALUE, because vertical values are now a value refusal.
• The seams property-order pin gains the family, and the writing-mode registry test checks that it sits between background and grid.
• pixel-reference glyph-clearance pins gain WM-0's four cases. With those cases removed, the old pins and bottom-scanlines hold exactly.
• The css-escapes count goes from 13732 to 13778: +46 declarations from the new properties, all read the same by Chrome and Dragon.

Regenerated outputs are in their own commits, each naming its commands. A second run changes nothing, and existing outputs change only in their emitted-CSS compilation header.

Passed (macOS, after merging origin/master b41500f)

• pnpm typecheck
• pnpm test: 124 files, 2541/2541
• pnpm wpt:check --target web: every entry matches, with no pass/fail status change
• parity:lanes --run-device on iOS and Android, 392 cases per DPR:
  • layout-vectors-device, frames, applied and lines pass;
  • device-pixels fails with master's exact counts (iOS 135, Android 182), and the device-failures files are unchanged and name no writing-mode case.

This is the "P5 device step for WM-0's 4 cases" that HANDOFF.md listed as pending.

🤖 Generated with Claude Code

Catch-up (c0204fd): merged origin/master 74d72d9 (#43 V1b, #38 MQ-a); only generated files conflicted, taken from master and regenerated to a fixed point (media-sweep --check 18/18). Glyph-clearance pins in pixel-reference.test.ts = merge base + WM-0 increments + V1b increments. Device lanes, 460 cases per DPR: frames/applied/lines/layout-vectors pass on iOS and Android; device-pixels iOS 135 / Android 182, equal to master, same per-case breakdown, no writing-mode case. pnpm typecheck; pnpm test 132 files / 2904 tests; wpt:check --target web pass.

Note

Accept horizontal-tb for writing-mode; refuse vertical values

• Adds writing-mode, text-orientation, and text-combine-upright as inherited no-longhand properties registered in properties.ts and the generated grammar
• New shorthand handlers in writing-mode.ts accept only horizontal-tb plus SVG legacy horizontal aliases; vertical values emit a DRAGON_UNSUPPORTED_VALUE diagnostic at the offending token. text-combine-upright values with the digits keyword are refused
• stylesheet.ts now returns a diagnostic for zero-longhand shorthands with a refusal function instead of parsing unchecked
• Adds parity fixtures, layout vectors, and expected snapshots for horizontal and inert-text writing-mode cases in LTR and RTL, and rejection fixtures for vertical, sideways, legacy, and digit values
• Updates WPT expectations in web.json so unsupported vertical writing-mode tests report unsupported-value diagnostics
• Risk: dual.ts now uses horizontal-tb as the Dragon reset value for writing-mode when resolving reset longhands; check WRITING_MODE_RESET_LONGHANDS consumers if capture data is missing the property

^{Macroscope summarized c0204fd.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This change adds production-facing support for a previously refused CSS property family and changes handling of variable-backed declarations, while also updating grammar, support profiles, and extensive parity artifacts. The rendered impact is intentionally limited and well covered, but the broadened acceptance behavior warrants human review.

^{You can add or adjust custom eligibility rules. Learn more.}

Dismissing prior approval to re-evaluate c0204fd