fix(showcase): register Mark Done action handler via inline body (#2169)

The `showcase_mark_done` action was declared `type: 'script'` but carried
neither a `body` nor a `target` handler, so AppPlugin never registered an
engine handler for it. Clicking "Mark Done" therefore hit
`POST /actions/showcase_task/showcase_mark_done`, fell through to the `'*'`
wildcard lookup, and returned `Action 'showcase_mark_done' on object '*' not
found` — surfaced in the UI as an error.

Add an L2 sandboxed `body` that flips the dedicated `done` flag and
`progress` to 100. It deliberately avoids writing `status: 'done'`: the
`task_status_flow` state-machine only permits `in_review -> done`, so a
direct status write would be rejected from Backlog/To Do/In Progress rows.
Using the `done` boolean lets the action succeed from any state.

Verified in-browser (green "Task marked done." toast, no errors) and via
API regression on an In Progress task; `pnpm verify` green (typecheck + 22 tests).

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

@@ -10,13 +10,37 @@ const task = 'showcase_task';
  * record header/more, related list, global nav).
  */
 
-/** script — inline handler, shown on each row and the record header. */
+/**
+ * script — inline sandboxed handler, shown on each row and the record header.
+ *
+ * The `body` (L2 sandboxed JS) is what makes this action *executable*: AppPlugin
+ * walks the bundle's actions on bind and only registers an engine handler for
+ * those carrying a `body` (or `target` -> bundle function). Without it the
+ * runtime has nothing to invoke and `POST /actions/showcase_task/showcase_mark_done`
+ * fails with "Action ... not found".
+ *
+ * It flips the dedicated `done` flag and `progress` rather than the `status`
+ * select on purpose: `status` is governed by the `task_status_flow`
+ * state-machine (only `in_review -> done` is a legal direct jump), so writing
+ * `status: 'done'` from a Backlog/To Do/In Progress row would be rejected. The
+ * `done` boolean is the completion flag that works from any state.
+ */
 export const MarkDoneAction = defineAction({
   name: 'showcase_mark_done',
   label: 'Mark Done',
   icon: 'check',
   objectName: task,
   type: 'script',
+  body: {
+    language: 'js',
+    source:
+      "var id = ctx.recordId || (ctx.record && ctx.record.id) || input.recordId;" +
+      "if (!id) throw new Error('No record to mark done');" +
+      "await ctx.api.object('showcase_task').update({ id: id, done: true, progress: 100 });" +
+      "return { ok: true, id: id };",
+    capabilities: ['api.write'],
+  },
+  successMessage: 'Task marked 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.