Radix UI -> Base UI migration

You migrate shadcn wrappers, hand-rolled radix compositions, and their consumers to @base-ui/react, keeping the project buildable at every step. Be precise; never guess a mapping. When a prop or part is not in these reference files, check node_modules/@base-ui/react/**/*.d.ts before transforming, and record gaps in the report.

Preflight (always)

1. npx shadcn@latest info --json (or the project's runner): gives the current base, STYLE (e.g. radix-lyra), tailwind version, aliases, installed components, and package manager. Trust it over inference.
2. Detect the package manager (packageManager field / lockfile: pnpm-lock.yaml, bun.lock, yarn.lock, package-lock.json) and use IT for every install. Never leave a stale lockfile.
3. Require a clean git tree; work on a branch; one commit per component.
4. Baseline check BEFORE touching dependencies: run the project's typecheck/build so pre-existing failures are never attributed to you.
5. Install @base-ui/react alongside radix. Radix packages are removed only after the LAST component is migrated (both coexist fine).

Strategy: golden pair first, transformation engine second

• Golden pair via the CLI (preferred). If the project is shadcn with a known style (radix-<style>), the shadcn CLI itself is the golden-pair executor:
  1. Classify each ui wrapper FIRST: diff the user's file against its stock origin, using the components.json style VERBATIM in the URL (https://ui.shadcn.com/r/styles/<style>/<component>.json, files[0].content). This works for prefixed styles (radix-nova) AND legacy unprefixed ones (new-york, new-york-v4, default), which are all still served.
  2. WHOLE-PROJECT mode: flip components.json style radix-<style> -> base-<style> now. PROGRESSIVE mode: do NOT flip yet (the project is still mostly radix; the flip happens once, after the last component); fetch base variants directly by URL instead (https://ui.shadcn.com/r/styles/base-<style>/<component>.json).
  3. PRISTINE wrappers, whole-project mode: shadcn add <component> --overwrite delivers the base variant with the project's exact icon/font/preset resolution. Never bulk --all --overwrite; go component by component, or you drown in unrelated registry version drift. PROGRESSIVE mode: never use --overwrite (it destroys the original that consumers still import); write the fetched base variant content to <component>-base.tsx instead.
  4. CUSTOMIZED wrappers: fetch the base variant and replay the user's diff onto it (their customizations must SURVIVE; --overwrite would destroy them). Mechanical implementation that works at scale: git merge-file user.tsx radix-golden.tsx base-golden.tsx (three-way merge, radix golden as ancestor) auto-resolves most files; hand-resolve conflicts with the reference tables.
  5. MANDATORY leftover sweep on EVERY golden-pair file, including ones that merged "clean": grep -n "radix-ui\|@radix-ui\|IconPlaceholder" per file. The registry sometimes reorders functions between variants, which makes three-way merges report zero conflicts while leaving stale radix hunks in place. A clean merge is NOT proof of a clean file. This is more reliable than reconstructing transforms; use it whenever the pair exists. Consumer/app code has no CLI mechanism: always hand-migrate it against consumer-props.md.
• Legacy styles (new-york, new-york-v4, default): classification only, no replay. These have no base counterpart (there is no base-new-york), and retargeting onto a base-<style> variant would restyle the user's app. Use the radix golden ONLY to detect customizations, then run the transformation engine on the user's OWN file: rewire primitives, keep their exact classes, apply class-mapping renames. Their look stays theirs. At the end of a legacy whole-project migration, FLAG (do not fix): the style name still reads as radix to the CLI, so future shadcn add will deliver radix variants; the user decides whether to switch style or add manually.
• Transformation engine (fallback). Hand-rolled radix code, non-shadcn projects, unknown styles: transform using universal-patterns.md (imports in BOTH forms: radix-ui and @radix-ui/react-*; asChild->render with the worked example; Portal>Positioner>Popup; the positioner FORWARD rule; part renames), the per-family props tables (overlays.md, menus.md, form-controls.md, disclosure.md, display-misc.md), class-mapping.md for data-attribute/CSS-var rewrites, and wrapper-shapes.md for exact target shapes (tooltip arrow, SubContent defaults, select anatomy).

Modes

Progressive (default). "Migrate accordion" = one component, strangler-fig:

1. Detect in-progress state first: an existing <component>-base.tsx, consumers split between old/new imports. The files ARE the state; resume, never restart.
2. If the component imports other ui wrappers still on radix (select -> button), STOP and recommend migrating those first, bottom-up.
3. Write the migrated version to <component>-base.tsx (original untouched; golden-pair content fetched by URL, or transformed by hand, per the strategy above); typecheck. Repoint consumers ONE AT A TIME (imports + the call-site props in consumer-props.md); typecheck each. When no consumer imports the original: delete it, rename -base -> original, flip imports back, final check, commit. When the LAST radix wrapper in the project is finalized, flip components.json to base-<style> and remove radix deps.

Whole project (only when explicitly asked): same per-component work in dependency order (leaf/shared wrappers like button and label first). After wrappers, sweep ALL app code against consumer-props.md — the call-site break surface is much larger than asChild. Then remove radix deps, install, full build.

Hard rules

• NEVER touch non-radix libraries or their wrappers: cmdk (command), vaul (drawer), sonner, input-otp, react-day-picker (calendar), recharts (chart). Report them as intentionally untouched.
• No Base UI counterpart: AspectRatio -> CSS aspect-ratio div; Label -> native <label>; VisuallyHidden -> sr-only; Direction -> Direction Provider (direction prop, not dir). Popover Anchor and NavigationMenu Indicator have no equivalent: inert passthrough + flag.
• button.tsx migrates to the REAL @base-ui/react/button primitive, never a hand-rolled useRender wrapper.
• Behavior deltas are FLAGGED, never silently patched (tabs manual activation, menu items not closing on click, nav-menu 50ms delay). The target is idiomatic Base UI matching the shadcn base registry.
• Honest reporting: skipped/reverted files are listed as flagged, never as migrated. Pre-existing failures are named as pre-existing.

Verify and report

Typecheck per file, build per batch, full build at the end vs the baseline.

Reports live in a .migration/ directory at the project root, ONE FILE PER COMPONENT: .migration/<component>.md (e.g. .migration/accordion.md). Rules:

• Each run writes (or fully overwrites) the file for each component it migrated. Re-running a component replaces its report; never touch other components' files.
• A multi-component run ("migrate alert-dialog and dropdown-menu") writes one file per component, each self-contained; shared consumer-sweep notes are repeated in every affected file.
• Whole-project mode writes the per-component files plus .migration/project.md (dependency swap, app-code sweep summary, final build result).
• There is NO index file. Migration status is derived from disk, not maintained: scan the project's ui directory (the ui alias from shadcn info, e.g. components/ui or src/components/ui) for remaining radix imports when asked "what's left". End every run's summary with that derived count ("N wrappers remain on Radix").

Each .migration/<component>.md uses EXACTLY this structure (it is documented publicly; reports must match it):

# <component>

<date, strategy used (golden pair via CLI / merge / engine), one-line verdict>

## Changed

<every file touched, with what changed and why; include file:line for
anything notable. Confirm the leftover scan is clean:
grep -n "radix-ui\|@radix-ui" on this component's files>

## Left alone

<files that look related but were intentionally not touched, with the reason
(cmdk/vaul/sonner are not radix; unrelated drift; etc.)>

## Behavior changes

<differences that compile fine but act differently; flagged, never patched
(tabs activation, menu close-on-click, delays...). Empty section if none>

## Verify by hand

<short manual QA checklist for this primitive family: focus return on
dialogs, keyboard nav + typeahead on menus/select, tooltip delay feel,
slider commit events. Concrete steps, one minute of clicking>