fix(showcase): hide Mark Done once the task is complete (#2183)

Mark Done lingered on already-done records and re-firing it was a silent no-op
("why is it still here?"). Gate the action with `visible: '!record.done'` — the
`done` boolean this action sets, so the button disappears after a successful
click and stays hidden on finished tasks.

The `record.`-prefix is required: the ActionEngine filters a record-header
action's `visible` against `{ record, recordId, objectName, user }` with
fail-closed semantics (`throwOnError: true` → catch → hide). A bare `done` /
`status` predicate is not at the top level of that context, so it throws and
the action is hidden on EVERY record (the trap an earlier attempt hit). A single
operand is also deliberate — the renderer wraps `visible` as a `${...}` template
whose evaluator throws on compound `&&` / `||`.

Verified in-browser against a current console: shows on active tasks, hides on
done tasks; clicking it flips `done` and the button is gone on reload.

Co-authored-by: Jack Zhuang <277994282+os-zhuang@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: 3 people

examples/app-showcase/src/actions/index.ts

@@ -41,6 +41,14 @@ export const MarkDoneAction = defineAction({
     capabilities: ['api.write'],
   },
   successMessage: 'Task marked done.',
+  // Hide once the task is complete. Gate on `record.done` (the boolean this
+  // action sets) so the button vanishes after a successful click and stays
+  // hidden on finished records (the "why is it still here?" report). NOTE the
+  // `record.`-prefix: the ActionEngine evaluates a record-header action's
+  // `visible` against `{ record, recordId, … }` with fail-closed semantics, so
+  // a bare `done`/`status` throws (field not at top level) and silently hides
+  // the action. Single operand, too — the template path throws on `&&`/`||`.
+  visible: '!record.done',
   // `record_section` so the Task Detail page's `record:quick_actions` bar
   // (which names this action) resolves it — the engine location-filters even
   // explicitly-named actions, mirroring the platform's own sys-user pages.