sync shadcn copy fallback

Objective: Apply the accepted sync-shadcn rows for mdx/code-command-yarn-tab and mdx/copy-button-fallback: keep the already-synced yarn tab row verified, implement upstream-style copy fallback semantics for Plate copy helpers, mark the copy fallback row synced, and regenerate the sync dashboard.

Completion threshold: Complete when code-command-yarn-tab and copy-button-fallback both resolve to synced in docs/sync/shadcn/deltas.json and docs/sync/shadcn/dashboard.json, the copy helpers use a hidden-textarea fallback and only show copied state after successful writes, yarn command support remains wired through command props, types, config, and copy UI, the dashboard is regenerated, lastSyncedCommit stays unchanged, and all verification commands recorded below pass.

Verification surface:

apps/www/src/components/copy-button.tsx
apps/www/src/components/code-block-command.tsx
apps/www/src/components/command-menu.tsx
apps/www/src/lib/rehype-npm-command.ts
apps/www/src/types/unist.ts
apps/www/src/hooks/use-config.ts
docs/sync/shadcn/deltas.json
docs/sync/shadcn/dashboard.json
docs/sync/shadcn/status.json

Constraints:

Do not run build:registry.
Do not advance docs/sync/shadcn/status.json:lastSyncedCommit.
Do not mutate unrelated sync rows.
Preserve Plate analytics and dropdown copy helpers while adopting upstream success semantics.

Boundaries:

In scope: source edits for copy behavior, sync row state, dashboard regeneration, and this closeout plan.
Out of scope: broader MDX primitive adoption, screenshots for unrelated rows, registry output, baseline advancement, and unrelated shadcn deltas.

Blocked condition: Blocked only if the copy helper change cannot pass www typecheck, the dashboard cannot regenerate from deltas.json, or row state cannot be verified in both durable JSON surfaces.

Start Gates:

Gate	Applies	Evidence
`autogoal` loaded and active goal created	yes	Active goal created for the two accepted rows before mutable edits.
`sync-shadcn apply` mode established	yes	User requested explicit `pending -> synced` row transitions.
Current row state read	yes	`deltas.json` showed yarn already `synced` and copy fallback awaiting sync.
Upstream reference checked	yes	`../shadcn/apps/v4/components/copy-button.tsx` confirmed fallback and success-gated behavior.
Baseline semantics read	yes	`status.json` keeps `lastSyncedCommit` at `4a4dc8eb0fc793d8e9225e780183ad605f15d2c2`.

Work Checklist:

Verified code-command-yarn-tab already has local yarn command support.
Added hidden-textarea fallback for restricted clipboard environments.
Made copyToClipboardWithMeta return a success boolean.
Gated copied state on successful clipboard writes in copy buttons.
Preserved Plate copy analytics and dropdown helpers.
Marked copy-button-fallback synced in deltas.json.
Regenerated docs/sync/shadcn/dashboard.html and dashboard.json.
Verified row state, JSON parse, source evidence, lint, and www typecheck.
Left lastSyncedCommit unchanged because only selected rows were applied.

Completion Gates:

Gate	Applies	Required action	Evidence
Accepted row state	yes	Verify both requested rows are `synced`	Dashboard JSON extraction returned both rows with `state: synced`.
Yarn row preservation	yes	Verify yarn source wiring remains present	`rg` found `__yarnCommand__`, yarn config union, and yarn command tab/copy support.
Copy fallback behavior	yes	Verify fallback and success-gated state exist	`rg` found `legacyCopyToClipboard`, async copy helper, awaited copy calls, and gated state updates.
Dashboard regeneration	yes	Run sync dashboard builder	`pnpm sync-shadcn dashboard` completed and wrote dashboard HTML/JSON.
JSON validity	yes	Parse durable sync JSON	Node parsed `deltas.json` and `dashboard.json` successfully.
Source typecheck	yes	Run app typecheck after lint fix	`pnpm --filter www typecheck` passed after final lint formatting.
Lint formatting	yes	Run repo lint fixer	`pnpm lint:fix` passed after checking 3154 files.
Dashboard script syntax	yes	Check dashboard builder syntax	`node --check .agents/rules/sync-shadcn/scripts/build-dashboard.mjs` passed.
Baseline advancement	no	Keep sync baseline unchanged	`status.json` still reports `lastSyncedCommit` `4a4dc8eb0fc793d8e9225e780183ad605f15d2c2`.
Browser proof	no	No visible layout change in this apply slice	Copy behavior is source/typechecked; no screenshot needed for this row.
Registry/template output	no	Avoid CI-controlled generated registry/template output	No registry build or template edit performed.
Goal plan complete	yes	Run autogoal completion check	Recorded for final closeout.

Phase / pass table:

Phase	Status	Evidence	Next
Intake and baseline read	done	Row states and status baseline read	none
Implementation	done	Copy fallback and success-gated state implemented	none
Sync metadata	done	`copy-button-fallback` marked synced and dashboard regenerated	none
Verification	done	Typecheck, lint, JSON, syntax, and source audits passed	none
Closeout	done	This plan records final evidence	none

Verification evidence:

pnpm sync-shadcn dashboard passed and wrote docs/sync/shadcn/dashboard.html plus docs/sync/shadcn/dashboard.json.
node --check .agents/rules/sync-shadcn/scripts/build-dashboard.mjs passed.
Node JSON parse passed for docs/sync/shadcn/deltas.json and docs/sync/shadcn/dashboard.json.
Dashboard JSON extraction returned code-command-yarn-tab and copy-button-fallback with state: synced.
Focused rg audit found yarn command plumbing and copy fallback/success semantics in the source files listed above.
pnpm lint:fix passed after checking 3154 files.
pnpm --filter www typecheck passed after the lint formatting pass.

Reboot status: The apply slice is complete. If resumed, only run the autogoal completion check and close the active goal; no implementation or metadata work remains.

Open risks: None for these two rows. Remaining MDX and Code Primitive rows are separate dashboard work and intentionally remain outside this apply slice.