fix(console,plugin-form): render a form section that references a field group (#8641)

.changeset/8641-console-formpage-section-group.md

@@ -0,0 +1,51 @@
+---
+'@object-ui/plugin-form': minor
+'@object-ui/console': patch
+---
+
+Render a form section that REFERENCES a field group on the console's form page,
+and publish the resolver that does it (objectui#8641).
+
+`@objectstack/spec` 17.3.0 lets a `form.sections[]` entry declare its members
+either way — enumerate `fields`, or point `group` at one of the object's declared
+`fieldGroups` (objectstack#13855, ADR-0085 §5). `apps/console`'s `FormPage` has
+its own section builder, on none of `@object-ui/plugin-form`'s code path, and it
+read `sec.fields ?? []` and `sec.label` — neither of which a `{ group }` section
+carries. Measured in the DOM on both routes before the fix: the `<section>` was
+emitted with its border and padding and then stood **empty** — no heading, no
+inputs, no diagnostic — so a submitter saw a blank card where the group's fields
+belong. The same silent-drop class objectui#7051 closed on the `plugin-form`
+chain, at the third consumer.
+
+Newly importable from `@object-ui/plugin-form` — one function and the options
+type its signature requires, nothing else:
+
+```typescript
+import {
+  resolveSectionGroupReferences,
+  type ResolveSectionGroupsOptions,
+} from '@object-ui/plugin-form';
+```
+
+- `resolveSectionGroupReferences(sections, { objectName, formType, objectDef })`
+  — replace every `{ group: 'x' }` section with the section that group declares
+  (label, members, description, collapse state), leaving everything else
+  untouched. With no reference in the list it returns its input **by identity**,
+  so it cannot perturb an existing form and is safe inside a `useMemo`. An
+  unresolvable reference yields an empty section, never a dropped one, and is
+  reported once naming the object and the key.
+
+`hasSectionGroupReference`, `resetSectionGroupReports`, `GROUP_OWNED_SECTION_KEYS`
+and `SECTION_LAYOUT_KEYS` stay module-private, pinned as the withheld set.
+
+⛔ No assembly rule is re-implemented on the console side: declared order, the
+empty-group drop, the ungrouped trailing bucket and the collapse / `visibleWhen`
+passthrough all reach it from `deriveFieldGroupLayout` through this package's one
+adapter — the same code path `ObjectForm` resolves through — which is why the
+resolver is exported rather than the derivation being read a second time.
+
+`ObjectSchemaPayload` in the console now carries `fieldGroups`, and its internal
+`/meta/object/:name` loader copies the key: that rebuild is key by key, so an
+uncopied key is gone before the builder can see it.
+
+No behaviour change for any form that does not author `group`.