diff --git a/.changeset/21284-detail-entry-describes.md b/.changeset/21284-detail-entry-describes.md
new file mode 100644
index 00000000000..d59378e53a7
--- /dev/null
+++ b/.changeset/21284-detail-entry-describes.md
@@ -0,0 +1,12 @@
+---
+'@objectstack/spec': patch
+---
+
+docs(spec): an `object-master-detail-form` detail entry's `inlineMode` and `formFields` describes say what happens when the key is omitted on both of the renderer's paths (#21284)
+
+Clause-②: no
+
+- **Derived entry** (any entry that does not name both `relationshipField` and at least one column): an omitted `inlineMode` is resolved from the relationship field's `inlineEdit`, else from the child object's shape, and an omitted `formFields` is derived from the child object's fields. This is unchanged.
+- **Entry kept as authored** (one that names both `relationshipField` and at least one column): the renderer resolves and derives nothing. An omitted `inlineMode` renders the collection as a grid, which offers the per-row form only when `formFields` lists more fields than `columns`. An omitted `formFields` means the per-row form is offered only when `inlineMode` is `form`, and it then draws the child object's full field list.
+- The `inlineMode` describe used to say only "resolved from the relationship field's `inlineEdit` when omitted", and the `formFields` describe only "derived from the child object's editable fields when omitted". Neither holds for an entry kept as authored. The `formFields` describe also no longer says "editable": the derived list keeps `readonly` fields, as `deriveInlineRowFormFields` (`@objectstack/spec/data`) does.
+- No schema accepts or refuses anything new. Only the two describes, the reference page that lifts them, and one source comment change.
diff --git a/content/docs/references/ui/component.mdx b/content/docs/references/ui/component.mdx
index a8c1d725f1a..bcda35e83eb 100644
--- a/content/docs/references/ui/component.mdx
+++ b/content/docs/references/ui/component.mdx
@@ -976,8 +976,8 @@ Sort field and direction pair
 | **childObject** | `string` | ✅ | Child object whose records are entered inline |
 | **relationshipField** | `string` | optional | FK on the child pointing back to the parent (auto-detected from the child's master_detail/lookup field when omitted) |
 | **columns** | `{ name: string; label?: string; type?: Enum<'text' \| 'number' \| 'currency' \| 'date' \| 'datetime' \| 'time' \| 'select' \| 'lookup' \| 'file'>; width?: number; … }[]` | optional | Editable grid columns (derived from the child object when omitted). Each entry is the strict, name-keyed inline grid column a relationship field's `inlineColumns` takes (`{ name, label?, type?, … }` — objectui GridColumn); identity-only entries (`{ name }`) hydrate everything else from the child object's fields. Unknown keys and the retired `field` spelling are refused at parse. |
-| **formFields** | `string[]` | optional | Child field names for the per-row expand form (derived from the child object's editable fields when omitted) |
-| **inlineMode** | `Enum<'grid' \| 'form'>` | optional | Inline-edit form factor: 'grid' = editable cells; 'form' = read-only list + per-row full form. Resolved from the relationship field's `inlineEdit` when omitted |
+| **formFields** | `string[]` | optional | Child field names for the per-row expand form. When omitted they are derived from the child object's fields — except on an entry that names both `relationshipField` and at least one column, which is kept as authored: nothing is derived, and the per-row form is offered only when `inlineMode` is 'form', where it draws the child object's full field list |
+| **inlineMode** | `Enum<'grid' \| 'form'>` | optional | Inline-edit form factor: 'grid' = editable cells; 'form' = read-only list + per-row full form. When omitted it is resolved from the relationship field's `inlineEdit`, else from the child object's shape — except on an entry that names both `relationshipField` and at least one column, which is kept as authored: nothing is resolved, the collection renders as a grid, and the per-row form is offered only when `formFields` lists more fields than `columns` |
 | **amountField** | `string` | optional | Numeric child column summed for the running total |
 | **sortField** | `string` | optional | Child field holding the line sort position, stamped on drag-reorder (derived from a `position` / `sort_order` / … field when omitted) |
 | **totalField** | `string` | optional | Parent field to receive the rolled-up sum |
diff --git a/packages/spec/src/ui/component.zod.ts b/packages/spec/src/ui/component.zod.ts
index 5eb2a657697..0d953a969ab 100644
--- a/packages/spec/src/ui/component.zod.ts
+++ b/packages/spec/src/ui/component.zod.ts
@@ -5006,7 +5006,8 @@ const MASTER_DETAIL_DETAIL_HISTORY =
  * child-collection surfaces. The three it adds are the renderer's own:
  * `formFields` (the per-row expand form), `inlineMode` (the two form factors
  * a relationship field's `inlineEdit` names; absence takes the relationship's
- * own resolution) and `sortField` (the line-position field the grid stamps on
+ * own resolution only on an entry the renderer derives, and its describe
+ * states both paths) and `sortField` (the line-position field the grid stamps on
  * drag-reorder). `title` and `addLabel` are plain strings because the
  * renderer draws them as a React child and a button label without resolving a
  * locale map.
@@ -5030,8 +5031,8 @@ function masterDetailDetailEntry() {
     childObject: z.string().describe('Child object whose records are entered inline'),
     relationshipField: z.string().optional().describe('FK on the child pointing back to the parent (auto-detected from the child\'s master_detail/lookup field when omitted)'),
     columns: z.array(InlineGridColumnSchema).optional().describe("Editable grid columns (derived from the child object when omitted). Each entry is the strict, name-keyed inline grid column a relationship field's `inlineColumns` takes ({ name, label?, type?, … } — objectui GridColumn); identity-only entries ({ name }) hydrate everything else from the child object's fields. Unknown keys and the retired `field` spelling are refused at parse."),
-    formFields: z.array(z.string()).optional().describe("Child field names for the per-row expand form (derived from the child object's editable fields when omitted)"),
-    inlineMode: z.enum(['grid', 'form']).optional().describe("Inline-edit form factor: 'grid' = editable cells; 'form' = read-only list + per-row full form. Resolved from the relationship field's `inlineEdit` when omitted"),
+    formFields: z.array(z.string()).optional().describe("Child field names for the per-row expand form. When omitted they are derived from the child object's fields — except on an entry that names both `relationshipField` and at least one column, which is kept as authored: nothing is derived, and the per-row form is offered only when `inlineMode` is 'form', where it draws the child object's full field list"),
+    inlineMode: z.enum(['grid', 'form']).optional().describe("Inline-edit form factor: 'grid' = editable cells; 'form' = read-only list + per-row full form. When omitted it is resolved from the relationship field's `inlineEdit`, else from the child object's shape — except on an entry that names both `relationshipField` and at least one column, which is kept as authored: nothing is resolved, the collection renders as a grid, and the per-row form is offered only when `formFields` lists more fields than `columns`"),
     amountField: z.string().optional().describe('Numeric child column summed for the running total'),
     sortField: z.string().optional().describe('Child field holding the line sort position, stamped on drag-reorder (derived from a `position` / `sort_order` / … field when omitted)'),
     totalField: z.string().optional().describe('Parent field to receive the rolled-up sum'),