fix(spec): reportForm offers a joined block's dataset as the ref:dataset picker, marked required

The "Joined blocks" repeater's `dataset` row declared only a label, so Studio's
report inspector drew a free-text, unmarked cell for a key the joined arm of
ReportSchema now refuses when absent (#21702). The row now declares
`widget: 'ref:dataset'` (registered in objectui's WIDGETS at the console pin)
and `required: true`, and a pin beside the refusal's own tests holds both.

Claude-Session: https://claude.ai/code/session_01T9u38rswFp5Rw8DswRUReJ
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/spec/src/ui/report-joined-block-dataset.test.ts

@@ -27,6 +27,7 @@ import { describe, expect, it } from 'vitest';
 import { getMetadataTypeSchema } from '../kernel/metadata-type-schemas';
 import { MIGRATIONS_BY_MAJOR, RETIRED_KEYS_BY_MAJOR } from '../migrations/registry';
 import { ObjectStackDefinitionSchema, defineStack } from '../stack.zod';
+import { reportForm } from './report.form';
 import { JoinedReportBlockSchema, ReportSchema, defineReport } from './report.zod';
 
 const ENTRY_ID = 'ui-report-joined-block-dataset-required';
@@ -245,6 +246,22 @@ describe('the joined reports measured at the census parse unchanged', () => {
   });
 });
 
+describe('the report form offers a block\'s `dataset` as the dataset picker, marked required (#21714)', () => {
+  it('the "Joined blocks" repeater\'s `dataset` row declares `widget: \'ref:dataset\'` and `required: true`', () => {
+    // Studio's report inspector renders this row spec: the widget hint picks
+    // the cell's control, and `required` draws the column's marker and the
+    // cell's `aria-required`. Without both, a new block is a free-text cell the
+    // refusal above rejects on save.
+    const blocks = (reportForm.sections as any[])
+      .flatMap((s) => s.fields ?? [])
+      .find((f: any) => f?.field === 'blocks');
+    expect(blocks?.type).toBe('repeater');
+    const row = (blocks.fields as any[]).find((f) => f?.field === 'dataset');
+    expect(row?.widget).toBe('ref:dataset');
+    expect(row?.required).toBe(true);
+  });
+});
+
 describe('the ADR-0087 ledger', () => {
   it('registers one D3 entry at protocol 18, with no D2 conversion, prescribing the binding', () => {
     const entries = MIGRATIONS_BY_MAJOR[18]!.semantic.filter((e) => e.id === ENTRY_ID);

packages/spec/src/ui/report.form.ts

@@ -82,7 +82,11 @@ export const reportForm = defineForm({
             // A `chart` input sat here until #20161: the key was removed from
             // `JoinedReportBlockSchema` because no renderer ever drew a block
             // chart, so this control offered a setting that plotted nothing.
-            { field: 'dataset', label: 'Dataset' },
+            // #21714: a joined report refuses a block that binds no `dataset`
+            // (#21702), so this column declares the `ref:dataset` picker the
+            // top-level binding declares, marked required: a block is bound
+            // in the form before save.
+            { field: 'dataset', label: 'Dataset', widget: 'ref:dataset', required: true },
             { field: 'rows', label: 'Rows' },
             { field: 'columns', label: 'Columns' },
             { field: 'values', label: 'Values' },