| name | mosaic |
| description | Work on Mosaic UI: styling a component with StyleX (`stylex.create`, `--cl-*` tokens, `themeProps`), or building a flow — writing the model (the Clerk adapter), the controller (local state, in React state or a state machine: `setup`, states/guards/`invoke`, wired to React with `useMachine`/`useActor`/ `useSelector`), or the view (rendering), testing any of those layers, or migrating a legacy / pre-Mosaic component into the model / controller / view split. Use when building, styling, debugging, testing, or migrating anything Mosaic. `references/mosaic-architecture.md` (repo root) holds the design-system contract; this skill is the how-to layer. |
Mosaic UI
Two things live under Mosaic, and this skill covers the how-to for both:
- Styled components are authored with StyleX —
stylex.create declares
the styles, themeProps emits the part's public identity (the .cl-<slot>
class plus data-<axis> attrs), and mergeStyleProps fuses the two with the
consumer's className/style.
- Flows follow a model → controller → view split — where the data comes
from → what the user is doing to it → what that looks like. What crosses
each boundary is plain data: no Clerk resource reaches the controller, no
machine snapshot reaches the view.
model Clerk adapter: reads Clerk hooks and resources, resolves the
environment, gates permissions, and answers with plain data plus
plain callbacks under an explicit `status`. The only layer that may
import Clerk hooks or call Clerk resource methods.
controller Local state: what is open, what is in flight, what the view may do
next — held in React state or a state machine, whichever the
interaction's complexity calls for. Wraps the model's callbacks so
an action can report pending, hold the surface still while it runs,
and close on success. No Clerk imports.
view Rendering: takes plain props and callbacks, renders UI, calls them
back. No Clerk imports. No data-fetching. No machine snapshot.
A machine is not a fourth layer, and not a requirement. It is one of the two
ways a controller can hold its state, and picking one is a complexity call:
useState for a boolean that never touches async, a machine once the
interaction has an async lifecycle or two values that must change together, and
sometimes both in one controller. Either way the controller returns plain props,
so the view cannot tell and neither can its tests. Criteria and worked
before/afters: packages/ui/src/mosaic/machine/ADOPTION.md.
references/mosaic-architecture.md (repo root, read by all agents) is the
canonical contract for the whole design system — the --cl-* tokens, the
.cl-<slot> + data-<axis> styling API, the CSS build, and the "Flow and data
architecture" section that defines the split. Read it for the what; this skill
is the how-to.
packages/ui/src/mosaic/user-button/ is the fullest worked example of the split
in the repo — model, controller, view, wrapper, types, messages, and a test per
layer. Copy from it.
Which reference to read
| You are… | Read |
|---|
Building on / authoring a headless primitive (@clerk/headless) | references/headless.md |
Styling a component (tokens, stylex.create, themeProps, CSS build) | references/stylex.md |
| Building an enter/exit transition, or any motion that reads as wrong | references/motion.md |
Writing the model (the Clerk adapter, status, permissions) | references/models.md |
| Writing the controller (local state, pending, action wrapping) | references/controllers.md |
| Authoring or debugging a state machine, or wiring one to React | references/machines.md → in-tree machine/README.md |
| Writing the view (rendering plain props) | references/views.md |
| Testing a model, controller, or view | references/testing.md |
| Migrating a legacy component into Mosaic (the end-to-end workflow) | references/migration.md |
| Running the parity audit that guards a migration | references/parity-audit.md |
The migration workflow (migration.md) ties the flow references together: it
treats the legacy component as the spec and drives you through the model,
controller, and view layers, then verifies parity with parity-audit.md.
