Document Unstyled working rules

Author: alexstyl

AGENTS.md

@@ -22,6 +22,12 @@ Before pushing changes that touch Kotlin (`.kt`) files, you must run `jvmTest` a
 - Compose Unstyled promises that it will never take or force design choices on the user. Keep APIs focused on behavior, state, semantics, and slots so design systems can provide their own visuals, icons, animation, layout, and styling.
 - Modifier chains in public composables must always start with the `modifier` parameter before adding internal modifiers.
 
+## Working in Unstyled
+
+- Treat the rules in this file as product constraints, not preferences. If a change needs to break one of them, call that out explicitly before making the change.
+- When adding or changing APIs, keep the unstyled promise intact: expose behavior and extension points, not visual opinions.
+- Primitives must follow the WAI-ARIA Authoring Practices Guide patterns for semantics and accessibility: https://www.w3.org/WAI/ARIA/apg/patterns/. Verify this with semantic checks in unit tests.
+
 ## Design with Compose
 
 - Never use the old `shadow()` API as it uses Material Design's specs. Always prefer using `dropShadow()` (`androidx.compose.ui.draw.dropShadow`) instead.