R1.4: Zero-flash theme bootstrap

Short answer: Paired semantic tokens across light/dark modes. Without paired tokens the page flashes the wrong theme before the script runs.

Group: UI and mobile performance. Status: stable. Generated from the rule definitions; do not edit by hand.

Playground: https://brevio.pro/tools/agent-guard-playground?rule=R1.4

What it catches

Zero-flash theme bootstrap: paired semantic tokens across light/dark modes.

Why

Without paired tokens the page flashes the wrong theme before the script runs.

A bad example

:root { --bg: #fff; }  /* no dark value */

A good example

:root { --bg: #fff; }
:root[data-theme=dark] { --bg: #111; }

How it is checked

A one-line card in the prompt of a slice that touches matching files (dev_rules.slice_micro_rules).

How to silence it

A person can silence one finding with brevio-core: ignore R1.4 -- reason on the line or the line above. Without the reason it does not count. An agent cannot silence it: the agent hook and the MCP tools never honour the comment, and a pull request that adds one is reported until a reviewer allows it. Fixing the code is still the better answer.

To change what the rule flags, edit its definition in dev_rules.py or code_rules/__init__.py. That is a code change and is reviewed like one.

R1.5 No dead controls
R1.6 Accessible switch geometry
R1.7 LCP asset priority
R1.8 Async polling hygiene
Every rule