Rule: componentization

When to make a component

Extract when the same markup appears three times, or when a block has a name a person would use out loud ("the eyebrow", "the route card", "the phase panel").

Do not extract on the second occurrence. Two similar blocks often diverge; the premature abstraction costs more than the duplication.

Sizes

A component that exceeds ~120 lines of markup is doing two jobs. Split it.
A page that is a bare list of components with no markup of its own has been over-split. Pages are allowed to contain layout.

Boundaries

src/components/
  primitives/   Eyebrow, Rule, Callout, CodeBlock — no domain knowledge
  blocks/       RouteCard, PhasePanel, HandoffTable, SkillPackage — composed, page-agnostic
  islands/      interactive only; each one justified per rules/astro.md

Primitives never import blocks.
Blocks never import page-specific data; they take props.
Islands are leaves. An island must not wrap static children that could have been server-rendered.

Props

Typed interface Props, every field. No any, no untyped rest spread.
Required by default. Optional props need a default and a reason.
Pass data, not markup. If you find yourself passing an HTML string, you want a <slot>.

Named exports, no barrels

Import the file you need. Barrel index.ts files break tree-shaking and create import cycles; bulletproof-react advises against them and so do we.

The catalog is data, not components

The 24 review-desk entries are content, not 24 components. One SkillReviewCard.astro iterating a typed collection. If you are writing the 25th near-identical component, stop and model the data.

Do not componentize

hands-on/starter/ and hands-on/rules/ are lab fixtures. Their whole value is being flat, dependency-free files an attendee hands to an agent. They ship from public/ unchanged.

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