docs: define interaction modality architecture

[cixzhang]

Why

Components already share modality tracking and focus primitives, but the boundary between last-input modality and component focus ownership was implicit. That made programmatic-focus behavior easy to reinterpret component by component.

What

Adds one current architecture record that:

• defines programmatic focus visibility by the last input modality;
• separates shared modality state from component-owned focus paint;
• preserves existing family variation and state semantics; and
• names change coupling and verification evidence, including PR fix(chat): show composer focus ring for keyboard #5648 as a benchmark rather than authority.

Risk

Documentation only. No runtime behavior, visual design, or public API changes.

Testing

• pnpm exec prettier --check docs/architecture/interaction-modality.md
• pnpm check:knowledge
• pnpm check:changesets
• pre-commit check:repo

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Project	Deployment	Actions	Updated (UTC)
astryx	Ready	Preview	Aug 31, 2026 2:38am

[cixzhang]

/approve-spec 716204b

[github-actions]

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