[lanyue-llk]

Purpose

Expose preferred text scale through Stylo's CSS environment so Moli can update dependent styles through normal cascade and invalidation.

Overall design

Full-size overview · All current PR diagrams

Implementation flow (Mermaid)

flowchart LR
  M["Moli per-target emulation"] --> U["Device update API"]
  U --> V["Validate scale; invalid values become 1"]
  V --> E["env preferred-text-scale"]
  E --> C["CSS substitution and cascade"]
  C --> R["Recompute dependent styles"]
  F["Fixed author font sizes"] --> C

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Scope and integration

• Add the preferred text scale environment value and embedder update API.
• Validate values at the Device boundary.
• Keep fixed author sizes separate from values that depend on the environment.
• Retain the current WebMCP selector APIs required by the consumer's main branch.

Moli #731 pins head 0db9840e674f6ad45c4df06961501b1a26bd2827 and owns per-target updates and invalidation.

Reproduce the consumer badcase

The original browser-client scenario is v4_cdp_emulation_setemulatedostextscale. Moli lacked the command/state propagation and Stylo lacked the environment value. The full reproduction therefore runs through Moli #731's integration test, which pins this Stylo revision.

Input	Expected font size / width for env-based element	Fixed author font
scale 1.5	24px / 30px	16px
scale 2	32px / 40px	16px
clear scale	16px / 20px	16px

The fixture uses font-size:calc(16px * env(preferred-text-scale,1)) and width:calc(20px * env(preferred-text-scale,1)). It also updates color-scheme media preferences to check that scale changes preserve other environment state.

git clone https://github.com/lexmount/moli.git moli-review-text-scale
cd moli-review-text-scale
git checkout --detach fb2f6b397f359f2e7b98c59dce76b0a10fa03449
cargo nextest run -p moli-protocol \
  -E 'test(os_text_scale_updates_css_environment_and_preserves_media_preferences) | test(context_media_keeps_each_page_text_scale_across_reload)'

Use the repository's Rust toolchain and cargo-nextest. Expected result: both selected tests pass; failures show expected/actual CSS values. Fixtures are local and need no website deployment. #731's pinned Cargo dependency is the Stylo #1 head 0db9840e674f6ad45c4df06961501b1a26bd2827; the same source also preserves the WebMCP selector APIs.

Evaluation reports

• Moli #731 current-head CI: all 20 checks passed, including browser integration and the 1,020-case frontend differential.
• WebArena-Verified 812-task replay (frozen report edition): supporting historical evidence for the consumer stack. Its results are bound to the recorded binaries, not a fresh run of this Stylo revision.
• Stylo CI: Linux debug/release, macOS debug, Windows debug and the aggregate result all passed.

The consumer integration tests distinguish fixed font sizes from environment-dependent sizes and exercise recomputation after scale changes.