diff --git a/.changeset/21589-detail-entry-sort-field-retired.md b/.changeset/21589-detail-entry-sort-field-retired.md
new file mode 100644
index 00000000000..aa70334828f
--- /dev/null
+++ b/.changeset/21589-detail-entry-sort-field-retired.md
@@ -0,0 +1,36 @@
+---
+'@objectstack/spec': minor
+---
+
+feat(spec)!: an `object-master-detail-form` detail entry's `sortField` is retired — the console derives the line-position field from the child object and reads no authored value (#21589)
+
+Clause-②: no (narrowing)
+
+<!-- adr-0087: registered object-master-detail-form-detail-sort-field-removed, object-master-detail-form-detail-sort-field-retired -->
+
+**BREAKING** — an accept-set narrowing on a published authoring surface, shipped as `minor` under the launch-window convention for accept-set narrowings.
+
+`ComponentPropsMap['object-master-detail-form'].details[].sortField` named the child field the line grid stamps with each line's position on drag-reorder. The console stopped reading it: the field it stamps is derived from the child object, and the pinned console crossed that change while the spec still declared the key. So an authored `sortField` went through `os validate` clean and was dropped, and a drag-reorder stamped the derived field, or none (ADR-0049 enforce-or-remove).
+
+### FROM → TO
+
+| before | what to write instead |
+| --- | --- |
+| `details: [{ childObject: 'crm_invoice_line', sortField: 'line_no' }]` | delete `sortField`. The grid stamps the child object's first field named `position`, `sort_order`, `sequence`, `line_no`, `line_number` or `sort`. |
+| `sortField` naming a field outside that list | give the child object one of those fields; the line order is kept there. |
+| an entry that names `relationshipField` and at least one column and gives every column a `type` | unchanged: the renderer keeps that entry exactly as authored, loads no child schema for it, and stamps no line position, before and after the upgrade alike. |
+
+**The one-line fix: delete `sortField` from every `object-master-detail-form` detail entry.** `os migrate meta --from 17` lists the mechanical edits for existing sources; apply them by hand.
+
+**What an author now sees.** Writing the key fails `tsc` (its input type is the retired-key mark), and `os validate`, `os build` and `os lint` report it as a `component-props-invalid` warning carrying the prescription at `properties.details.N.sortField`. A page that carries it still saves and loads: a page component's `properties` is not parsed on the metadata save or load path.
+
+### The retirement kit
+
+- **Tombstone.** `sortField` is a `retiredKey()` on the strict detail entry. Its prescription prints the derived field names from their one declaration, a module reached by relative import only (`data/inline-grid-sort-fields.ts`), which the derived inline-grid columns read too.
+- **D2 conversion `object-master-detail-form-detail-sort-field-removed`** (step 18, retired from the load path): a lossless delete of `sortField` from every `properties.details[]` entry of an `object-master-detail-form`, scoped by component type and by position. Stored `sys_metadata` pages and built artifacts replay it, one notice per entry.
+- **D3 entry `object-master-detail-form-detail-sort-field-retired`** carries the judgment the delete cannot make: whether the child object declares the field the line order is kept in.
+- **`RETIRED_KEYS_BY_MAJOR[18]`** registers the nested key `ui/ObjectMasterDetailFormProps:details.sortField`.
+- **`record:line_items`' answer to `sortField`** no longer sends the author to the detail entry: no block takes an authored `sortField` any more.
+- **No deprecation window**: the writer census is zero.
+
+**Measured producers: none.** On origin/main 9a4182a752, no `object-master-detail-form` detail entry in `examples/`, `apps/`, `packages/`, `skills/` or `content/docs/` writes `sortField`, against the sibling detail-entry key `addLabel` on the showcase project workspace's entry as the control, through the same instrument. At the objectui pin `89cad75d5570` the only detail entries that write it are probes asserting that nothing reads it. Deployed metadata NOT MEASURED.
diff --git a/content/docs/references/ui/component.mdx b/content/docs/references/ui/component.mdx
index ae8afe2f215..734d6365349 100644
--- a/content/docs/references/ui/component.mdx
+++ b/content/docs/references/ui/component.mdx
@@ -1084,7 +1084,7 @@ Sort field and direction pair
 | **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 and the `totalField` rollup. When omitted it is picked from the grid's number and currency columns: a computed one, else one named `amount`, `total`, `subtotal`, `line_total`, `line_amount` or `net_amount`, else the last currency column, else the last numeric one — except on an entry that names `relationshipField` and at least one column and gives every column a `type`. The renderer keeps that entry exactly as authored, so nothing is picked. With no `amountField` authored or picked, the sums read a child column named `amount`, and the grid shows a running total only when `totalField` is set |
-| **sortField** | `string` | optional | Child field holding the line sort position, stamped on drag-reorder. When omitted it is the child object's first field named `position`, `sort_order`, `sequence`, `line_no`, `line_number` or `sort`, if it has one — except on an entry that names `relationshipField` and at least one column and gives every column a `type`. The renderer keeps that entry exactly as authored: nothing is derived, the grid stamps no line position, and a drag-reorder is not saved |
+| **sortField** | `never` | optional | [REMOVED] `object-master-detail-form` property `details[].sortField` was removed in @objectstack/spec 17 (ADR-0087 D2) — the console reads no authored value: the field the line grid stamps with each line's position on drag-reorder is derived from the child object, so an authored `sortField` was accepted and dropped. Delete the key. For a drag-reorder to be saved, give the child object a field named `position` / `sort_order` / `sequence` / `line_no` / `line_number` / `sort`: the renderer stamps the child's first field with one of those names — except on an entry that names `relationshipField` and at least one column and gives every column a `type`, which the renderer keeps exactly as authored and stamps no line position on. Run `os migrate meta --from 17` to list the mechanical edits for existing sources; apply them by hand. |
 | **totalField** | `string` | optional | Parent field to receive the rolled-up sum |
 | **title** | `string` | optional | Section title |
 | **minRows** | `number` | optional | Minimum number of rows |
diff --git a/packages/lint/src/validate-component-props.test.ts b/packages/lint/src/validate-component-props.test.ts
index a4f7cf10fd0..11e5c85aef6 100644
--- a/packages/lint/src/validate-component-props.test.ts
+++ b/packages/lint/src/validate-component-props.test.ts
@@ -91,6 +91,32 @@ describe('validateComponentProps — undeclared keys', () => {
     }
   });
 
+  // #21589 — an `object-master-detail-form` detail entry's `sortField` is a
+  // retiredKey tombstone, one array level down. The same door, the same
+  // warning: the finding names the entry's key, and the page is never refused.
+  it('reports a retired detail-entry `sortField` as a warning carrying the prescription, at the entry\'s key', () => {
+    const findings = validateComponentProps(
+      stackWith([
+        {
+          type: 'object-master-detail-form',
+          properties: {
+            objectName: 'invoice',
+            details: [
+              { title: 'Payments', childObject: 'invoice_payment' },
+              { title: 'Lines', childObject: 'invoice_line', sortField: 'line_no' },
+            ],
+          },
+        },
+      ]),
+    );
+    expect(findings).toHaveLength(1);
+    const [f] = findings;
+    expect(f.severity).toBe('warning');
+    expect(f.rule).toBe(COMPONENT_PROPS_INVALID);
+    expect(f.path).toBe('pages[0].regions[0].components[0].properties.details.1.sortField');
+    expect(f.message).toContain('`object-master-detail-form` property `details[].sortField` was removed in @objectstack/spec 17');
+  });
+
   it('walks components nested inside `properties` (tabs items → children)', () => {
     const findings = validateComponentProps(
       stackWith([
diff --git a/packages/spec/src/conversions/registry.ts b/packages/spec/src/conversions/registry.ts
index 2d89e2846e3..9de2376ad3b 100644
--- a/packages/spec/src/conversions/registry.ts
+++ b/packages/spec/src/conversions/registry.ts
@@ -12473,6 +12473,208 @@ const dashboardWidgetChartConfigStructureRemoved: MetadataConversion = {
   },
 };
 
+/**
+ * `object-master-detail-form`'s detail entry `sortField` leaves the contract
+ * (protocol 18, #21589 — ADR-0049 enforce-or-remove; the spec half of
+ * objectui#11070 round 9, the direction recorded on #21220's landing and
+ * mirrored on objectui#11396 ③: tombstone plus ADR-0087).
+ *
+ * **A pure lossless delete.** The console stopped reading the authored
+ * override at objectui `0a3e5409f`, and the `.objectui-sha` pin
+ * (`89cad75d5570`) is past it: `MasterDetailDetailConfig` has no `sortField`
+ * member (`plugin-form/src/MasterDetailForm.tsx:83`), and the field the line
+ * grid stamps with each line's position is the one `deriveDetail` derives from
+ * the child object (`deriveMasterDetail.ts:540`), handed to the grid as
+ * `sort_field` (`:874`). An authored value changed nothing on that console, so
+ * deleting it preserves observed behaviour exactly; the line order is kept by
+ * the child object's own field, which the entry's tombstone names. The
+ * tombstone refuses the key for a live author (advisory, via the props lint:
+ * `PageComponentSchema.properties` is an open bag).
+ *
+ * ⚠️ Scoped by component `type` and by POSITION — `properties.details[]` of an
+ * `object-master-detail-form` — never by key name: `sortField` is an ordinary
+ * name for an open-namespace component's own prop, and the fixture's
+ * non-carrier control is such a component authoring the same shape. A
+ * `details` entry that is not an object rides through untouched (the props
+ * gate reports it; it is not this entry's to fix).
+ *
+ * Zero authored occurrences in this repo's corpora at the retirement — no
+ * detail entry under `examples/`, `apps/`, `packages/`, `skills/` or
+ * `content/docs/` writes the key (control: the sibling detail-entry key
+ * `addLabel`, authored on the showcase project workspace's entry, same
+ * instrument, origin/main 9a4182a752) — so this entry exists for stored
+ * `sys_metadata` rows and for authors outside the repo, which the census could
+ * not measure.
+ */
+const objectMasterDetailFormDetailSortFieldRemoved: MetadataConversion = {
+  id: 'object-master-detail-form-detail-sort-field-removed',
+  toMajor: 18,
+  retiredFromLoadPath: true,
+  retiredAfter: '17.6.0',
+  surface: 'page.component.object-master-detail-form.details[].sortField',
+  summary:
+    "object-master-detail-form detail entry prop 'sortField' removed (the console reads no authored "
+    + 'value: the line grid stamps the field it derives from the child object, so the key was '
+    + "accepted and dropped; delete the key — the child object's own position field keeps the line order)",
+  apply(stack, emit) {
+    return mapPageComponents(stack, (component, path) => {
+      if (component.type !== 'object-master-detail-form') return component;
+      const properties = component.properties;
+      if (!isDict(properties) || !Array.isArray(properties.details)) return component;
+      const details = properties.details as unknown[];
+      let changed = false;
+      const nextDetails = details.map((entry, i) => {
+        if (!isDict(entry) || !('sortField' in entry)) return entry;
+        changed = true;
+        return stripKeys(entry, ['sortField'], emit, `${path}.properties.details[${i}]`);
+      });
+      if (!changed) return component;
+      return { ...component, properties: { ...properties, details: nextDetails } };
+    });
+  },
+  fixture: {
+    before: {
+      pages: [
+        {
+          name: 'invoice_entry',
+          regions: [
+            {
+              name: 'main',
+              components: [
+                // The carrier: a detail entry authoring the retired override,
+                // beside an entry WITHOUT it, which rides through untouched.
+                {
+                  type: 'object-master-detail-form',
+                  id: 'm1',
+                  properties: {
+                    objectName: 'crm_invoice',
+                    details: [
+                      { childObject: 'crm_invoice_line', title: 'Lines', sortField: 'line_no' },
+                      { childObject: 'crm_invoice_payment', title: 'Payments' },
+                    ],
+                  },
+                },
+                // ⚠️ The same shape on a component that is NOT an
+                // `object-master-detail-form` — its own prop, not this entry's
+                // key. Untouched: the strip is scoped by component type.
+                {
+                  type: 'acme:line_editor',
+                  id: 'x1',
+                  properties: { details: [{ childObject: 'crm_invoice_line', sortField: 'position' }] },
+                },
+                // A block whose entries carry no `sortField`, and one with a
+                // non-object entry: both ride through untouched, by reference.
+                {
+                  type: 'object-master-detail-form',
+                  id: 'm2',
+                  properties: { objectName: 'crm_order', details: [{ childObject: 'crm_order_line' }, 'crm_order_note'] },
+                },
+                // The nested position (#6775's lesson): a block inside a
+                // card's `children` is still a component.
+                {
+                  type: 'page:card',
+                  id: 'c1',
+                  properties: {
+                    children: [
+                      {
+                        type: 'object-master-detail-form',
+                        id: 'm3',
+                        properties: {
+                          objectName: 'crm_quote',
+                          details: [{ childObject: 'crm_quote_line', sortField: 'position' }],
+                        },
+                      },
+                    ],
+                  },
+                },
+              ],
+            },
+          ],
+        },
+        // The named-slot shape (#6776): the block authored into a slotted page.
+        {
+          name: 'invoice_entry_detail',
+          kind: 'slotted',
+          regions: [],
+          slots: {
+            details: {
+              type: 'object-master-detail-form',
+              id: 'm4',
+              properties: {
+                objectName: 'crm_invoice',
+                details: [{ childObject: 'crm_invoice_line', sortField: 'sequence' }],
+              },
+            },
+          },
+        },
+      ],
+    },
+    after: {
+      pages: [
+        {
+          name: 'invoice_entry',
+          regions: [
+            {
+              name: 'main',
+              components: [
+                {
+                  type: 'object-master-detail-form',
+                  id: 'm1',
+                  properties: {
+                    objectName: 'crm_invoice',
+                    details: [
+                      { childObject: 'crm_invoice_line', title: 'Lines' },
+                      { childObject: 'crm_invoice_payment', title: 'Payments' },
+                    ],
+                  },
+                },
+                {
+                  type: 'acme:line_editor',
+                  id: 'x1',
+                  properties: { details: [{ childObject: 'crm_invoice_line', sortField: 'position' }] },
+                },
+                {
+                  type: 'object-master-detail-form',
+                  id: 'm2',
+                  properties: { objectName: 'crm_order', details: [{ childObject: 'crm_order_line' }, 'crm_order_note'] },
+                },
+                {
+                  type: 'page:card',
+                  id: 'c1',
+                  properties: {
+                    children: [
+                      {
+                        type: 'object-master-detail-form',
+                        id: 'm3',
+                        properties: { objectName: 'crm_quote', details: [{ childObject: 'crm_quote_line' }] },
+                      },
+                    ],
+                  },
+                },
+              ],
+            },
+          ],
+        },
+        {
+          name: 'invoice_entry_detail',
+          kind: 'slotted',
+          regions: [],
+          slots: {
+            details: {
+              type: 'object-master-detail-form',
+              id: 'm4',
+              properties: { objectName: 'crm_invoice', details: [{ childObject: 'crm_invoice_line' }] },
+            },
+          },
+        },
+      ],
+    },
+    // Three notices: the region-level entry, the nested one and the slotted
+    // one. The open-namespace sibling and the entries without the key emit none.
+    expectedNotices: 3,
+  },
+};
+
 /**
  * `object.tenancy.organizationField` leaves the authorable surface (protocol
  * 18, #19054 — ADR-0049 enforce-or-remove; maintainer ruling 2026-09-18,
@@ -14598,6 +14800,7 @@ const MAJOR_18_CONVERSIONS: readonly OrderedConversion[] = [
   { conversion: objectGridDefaultSortRemoved, order: 14 },
   { conversion: objectGridResizableColumnsRemoved, order: 57 },
   { conversion: objectKanbanQuickAddRemoved, order: 15 },
+  { conversion: objectMasterDetailFormDetailSortFieldRemoved, order: 60 },
   { conversion: objectTenancyOrganizationFieldRemoved, order: 35 },
   { conversion: pageAssignedProfilesRemoved, order: 31 },
   { conversion: pageComponentFilterRecordToRuleArray, order: 36 },
diff --git a/packages/spec/src/data/inline-grid-columns.ts b/packages/spec/src/data/inline-grid-columns.ts
index 4c0884e40d5..3eedbed06ce 100644
--- a/packages/spec/src/data/inline-grid-columns.ts
+++ b/packages/spec/src/data/inline-grid-columns.ts
@@ -86,6 +86,11 @@
  * no expand control.
  */
 
+// The sort-position names live in their own module, reached by relative
+// import only: the retired `object-master-detail-form` detail entry
+// `sortField`'s prescription prints the same list (`ui/component.zod.ts`).
+import { INLINE_GRID_SORT_FIELDS } from './inline-grid-sort-fields';
+
 /** Default-visible column budget of a derived inline grid; the rest are `defaultHidden`. */
 export const DEFAULT_MAX_INLINE_GRID_COLUMNS = 6;
 
@@ -107,11 +112,6 @@ const INLINE_GRID_SYSTEM_FIELDS: ReadonlySet<string> = new Set([
   'organization_id', 'tenant_id', 'space', 'owner',
 ]);
 
-/** Field names that hold a line's sort position: the grid stamps them on drag-reorder. */
-const INLINE_GRID_SORT_FIELDS: ReadonlySet<string> = new Set([
-  'position', 'sort_order', 'sequence', 'line_no', 'line_number', 'sort',
-]);
-
 /** Field types a line-item cell cannot edit. File-family types are absent: they render an upload cell. */
 const INLINE_GRID_NON_EDITABLE_TYPES: ReadonlySet<unknown> = new Set([
   'formula', 'summary', 'rollup', 'autonumber', 'auto_number',
diff --git a/packages/spec/src/data/inline-grid-sort-fields.ts b/packages/spec/src/data/inline-grid-sort-fields.ts
new file mode 100644
index 00000000000..730899d294c
--- /dev/null
+++ b/packages/spec/src/data/inline-grid-sort-fields.ts
@@ -0,0 +1,40 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * The child field names that hold a line's sort position — ONE declaration,
+ * read by every place the spec states which field an inline grid stamps.
+ *
+ * The renderer derives the field it stamps with each line's position on
+ * drag-reorder from the child object: the first of these names the child
+ * declares (objectui `packages/plugin-form/src/deriveMasterDetail.ts`,
+ * `SORT_FIELD_NAMES`, the same six names in the same order at the
+ * `.objectui-sha` pin `89cad75d5570`). Two readers here:
+ *
+ * - `inline-grid-columns.ts`, whose derived grid columns and per-row form
+ *   fields skip these names, as the renderer's do;
+ * - `ui/component.zod.ts`, whose prescriptions for the retired
+ *   `object-master-detail-form` detail entry `sortField` name them: the
+ *   authored override is gone, so naming the child's field IS the remedy.
+ *
+ * Why a module of its own: both files must print the SAME list, never two
+ * copies of it, and exported from `inline-grid-columns.ts` it would ride the
+ * `data` barrel into the published API — a contract for what is the
+ * renderer's derivation rule, mirrored here so the spec's text agrees with it.
+ * This module is reached by relative import only, like
+ * `ui/action-target-aliases.ts`.
+ */
+
+/** Field names that hold a line's sort position: the grid stamps them on drag-reorder. */
+export const INLINE_GRID_SORT_FIELDS: ReadonlySet<string> = new Set([
+  'position', 'sort_order', 'sequence', 'line_no', 'line_number', 'sort',
+]);
+
+/**
+ * {@link INLINE_GRID_SORT_FIELDS} as a prescription prints it, in order:
+ * `` `position` / `sort_order` / … / `sort` ``. A module-level constant of a
+ * module that imports nothing, so it is initialised before any importer's body
+ * runs — `OS_EAGER_SCHEMAS=1` included.
+ */
+export const INLINE_GRID_SORT_FIELD_LIST: string = [...INLINE_GRID_SORT_FIELDS]
+  .map((name) => `\`${name}\``)
+  .join(' / ');
diff --git a/packages/spec/src/inline-grid-column-carriers.test.ts b/packages/spec/src/inline-grid-column-carriers.test.ts
index 4dcfe89ddb9..4c506cad903 100644
--- a/packages/spec/src/inline-grid-column-carriers.test.ts
+++ b/packages/spec/src/inline-grid-column-carriers.test.ts
@@ -425,7 +425,13 @@ describe('#20901 — the `field` → `name` respelling is a chain step on the fo
  */
 const MASTER_DETAIL_PROPS = ComponentPropsMap['object-master-detail-form'];
 
-/** Every key objectui's `MasterDetailForm` reads off a detail entry (the `.objectui-sha` pin `31971ff1e28f`). */
+/**
+ * Every key objectui's `MasterDetailForm` reads off a detail entry (the
+ * `.objectui-sha` pin `31971ff1e28f`, re-read at `89cad75d5570`). `sortField`
+ * is not one of them: the renderer derives the line-position field from the
+ * child object, and the key is a tombstone (#21589,
+ * `ui/master-detail-detail-sort-field-retirement.test.ts`).
+ */
 const FULL_DETAIL_ENTRY = {
   childObject: 'crm_invoice_line',
   relationshipField: 'invoice',
@@ -433,7 +439,6 @@ const FULL_DETAIL_ENTRY = {
   formFields: ['quantity', 'amount'],
   inlineMode: 'grid',
   amountField: 'amount',
-  sortField: 'position',
   totalField: 'total',
   title: 'Lines',
   minRows: 1,
@@ -543,7 +548,7 @@ describe('#20928 — the master-detail block\'s detail entry is strict, and its
       expect(result.success, JSON.stringify(result.error?.issues)).toBe(true);
       expect((result.data as { details: unknown[] }).details).toEqual([entry]);
     }
-    expect(Object.keys(FULL_DETAIL_ENTRY)).toHaveLength(12);
+    expect(Object.keys(FULL_DETAIL_ENTRY)).toHaveLength(11);
   });
 });
 
diff --git a/packages/spec/src/migrations/entries/retired-keys/18.ui__ObjectMasterDetailFormProps__details.sortField.ts b/packages/spec/src/migrations/entries/retired-keys/18.ui__ObjectMasterDetailFormProps__details.sortField.ts
new file mode 100644
index 00000000000..e90a3e693c3
--- /dev/null
+++ b/packages/spec/src/migrations/entries/retired-keys/18.ui__ObjectMasterDetailFormProps__details.sortField.ts
@@ -0,0 +1,23 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+// #21589 — ADR-0049 enforce-or-remove through the ADR-0087 D2 route, the spec
+// half of objectui#11070 round 9 (the direction recorded on #21220's landing
+// and mirrored on objectui#11396 ③: tombstone plus ADR-0087). The console
+// retired the authored override at objectui `0a3e5409f`, and the
+// `.objectui-sha` pin `89cad75d5570` is past it: `MasterDetailDetailConfig`
+// has no `sortField` member (`plugin-form/src/MasterDetailForm.tsx:83`), and
+// the field the line grid stamps with each line's position is the one
+// `deriveDetail` derives from the child object (`deriveMasterDetail.ts:540`),
+// handed to the grid as `sort_field` (`:874`). Tombstoned with `retiredKey()`
+// in the strict detail entry; a NESTED row (an array member, spelled without
+// its `[]`), so it has no `authorable-surface/` line and checks (b2)/(b3)
+// resolve it against the emitted schema. Stored and built pages are stripped
+// by the D2 conversion `object-master-detail-form-detail-sort-field-removed`,
+// a pure lossless delete scoped by component `type` and position; its D3
+// record is `object-master-detail-form-detail-sort-field-retired`.
+//
+// Registered under 18, not 17: the removal ships on the 17.x line
+// (launch-window convention: accept-set narrowings ride minor releases) and
+// the prescription lives at the major boundary where `migrate meta` users
+// look — the `ui/PageHeaderProps:breadcrumb` precedent.
+export const entry = 'ui/ObjectMasterDetailFormProps:details.sortField';
diff --git a/packages/spec/src/migrations/entries/semantic/18.object-master-detail-form-detail-sort-field-retired.ts b/packages/spec/src/migrations/entries/semantic/18.object-master-detail-form-detail-sort-field-retired.ts
new file mode 100644
index 00000000000..18c04d94f37
--- /dev/null
+++ b/packages/spec/src/migrations/entries/semantic/18.object-master-detail-form-detail-sort-field-retired.ts
@@ -0,0 +1,37 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+import type { SemanticMigration } from '../../types.js';
+
+// #21589 (ADR-0049 enforce-or-remove) — the D3 entry of the
+// `object-master-detail-form-detail-sort-field-removed` family (one D3 entry
+// per retirement family, even when D2 is lossless). Registered key:
+// `ui/ObjectMasterDetailFormProps:details.sortField`. The strip changes
+// nothing a user sees, because the console already ignored the authored
+// value; what it leaves is the one judgment a delete cannot make — whether the
+// child object carries the field the line order is kept in.
+export const entry: SemanticMigration = {
+  id: 'object-master-detail-form-detail-sort-field-retired',
+  // No backticks in `surface` — build-upgrade-guide.ts renders it inside a code
+  // span AND a table cell.
+  surface: 'page.component.object-master-detail-form.details[].sortField — a detail entry\'s '
+    + 'authored line-position field',
+  replacement: 'Nothing on the entry: delete the key. The line grid stamps each line\'s position into '
+    + 'the child object\'s own field, derived from the child object: its first field named '
+    + '`position`, `sort_order`, `sequence`, `line_no`, `line_number` or `sort`. To keep the line '
+    + 'order a drag-reorder sets, give the child object one of those fields (under the name the '
+    + 'deleted key named, when it is one of them).',
+  reason: 'The D2 conversion `object-master-detail-form-detail-sort-field-removed` deletes '
+    + '`sortField` from every `object-master-detail-form` detail entry, and the delete is lossless: '
+    + 'the console stopped reading the authored override, and the line grid stamps the field it '
+    + 'derives from the child object whatever the entry says. What the conversion cannot decide is '
+    + 'where the line order lives. An entry whose key named a field the derivation does not pick — '
+    + 'a name outside that list, or a second sort-named field after the first — saves its line '
+    + 'order into the derived field instead, or nowhere when the child object has none. An entry '
+    + 'that names `relationshipField` and at least one column and gives every column a `type` is '
+    + 'kept exactly as authored: no child schema is loaded for it, so no line position is stamped '
+    + 'and a drag-reorder is not saved, before and after the upgrade alike.',
+  acceptanceCriteria: 'No `object-master-detail-form` detail entry carries `sortField`; the props '
+    + 'lint reports one with the prescription. For each entry that had set it, the child object '
+    + 'declares the field the line order is kept in under one of the derived names, and after a '
+    + 'drag-reorder and save the lines reload in the order they were dragged into.',
+};
diff --git a/packages/spec/src/migrations/entries/semantic/18.ui-object-master-detail-form-details-closed.ts b/packages/spec/src/migrations/entries/semantic/18.ui-object-master-detail-form-details-closed.ts
index 66626b9d9fe..4a600a8a441 100644
--- a/packages/spec/src/migrations/entries/semantic/18.ui-object-master-detail-form-details-closed.ts
+++ b/packages/spec/src/migrations/entries/semantic/18.ui-object-master-detail-form-details-closed.ts
@@ -21,7 +21,7 @@ export const entry: SemanticMigration = {
     + 'grid columns), including `scale` on a column that declares no `type` and whose `name` is a '
     + '`currency` field of the entry\'s `childObject`',
   replacement: 'each entry is `{ childObject, relationshipField?, columns?, formFields?, '
-    + 'inlineMode?, amountField?, sortField?, totalField?, title?, minRows?, maxRows?, addLabel? }` '
+    + 'inlineMode?, amountField?, totalField?, title?, minRows?, maxRows?, addLabel? }` '
     + '— the keys the renderer reads — with `inlineMode` one of `grid` / `form`. Each column is the '
     + 'strict, name-keyed inline grid column a relationship field\'s `inlineColumns` takes — '
     + '`{ name, label?, type?, … }`, where `{ name }` alone hydrates the rest from the child '
diff --git a/packages/spec/src/migrations/entries/semantic/18.ui-record-line-items-props-closed.ts b/packages/spec/src/migrations/entries/semantic/18.ui-record-line-items-props-closed.ts
index ffa6a4c36de..bd14429b760 100644
--- a/packages/spec/src/migrations/entries/semantic/18.ui-record-line-items-props-closed.ts
+++ b/packages/spec/src/migrations/entries/semantic/18.ui-record-line-items-props-closed.ts
@@ -26,9 +26,10 @@ export const entry: SemanticMigration = {
     + '`{ name, label?, type?, options?, … }`. Write `name` where a column said `field` (or '
     + '`fieldName`, `key`); declare `label`, `type` and `options` on the column, because this block '
     + 'draws a column exactly as declared and hydrates nothing from the child object\'s field; '
-    + 'delete `scale` from a column declaring `type: \'currency\'`; delete `addLabel`, `sortField`, '
-    + '`formFields` and `inlineMode`, which belong to an `object-master-detail-form` detail entry and '
-    + 'are not read here, and any other key the shape does not declare.',
+    + 'delete `scale` from a column declaring `type: \'currency\'`; delete `addLabel`, `formFields` '
+    + 'and `inlineMode`, which belong to an `object-master-detail-form` detail entry and are not read '
+    + 'here, `sortField`, which no block takes (the detail entry derives the line-position field from '
+    + 'the child object), and any other key the shape does not declare.',
   reason: 'The block draws one inline grid of the record\'s child rows, through the same objectui '
     + 'grid as the other three carriers of the inline grid column, but it had no `ComponentPropsMap` '
     + 'row: it was the one entry on the string-arm registration ledger, so the component-props gate '
diff --git a/packages/spec/src/migrations/registry.ts b/packages/spec/src/migrations/registry.ts
index 69dffdc5eb9..59a00370297 100644
--- a/packages/spec/src/migrations/registry.ts
+++ b/packages/spec/src/migrations/registry.ts
@@ -5852,6 +5852,22 @@ const STEP18_RATIONALE: readonly RationaleFragment[] = [
       + 'is a pure lossless DELETE (the key never had an effect to preserve) scoped by component '
       + '`type`. Delete the key; `object-kanban` offers no quick-add control.',
   },
+  {
+    id: 'object-master-detail-form-detail-sort-field-retired',
+    order: 70,
+    text:
+      'It also retires an `object-master-detail-form` detail entry\'s `sortField` (#21589, ADR-0049 '
+      + 'enforce-or-remove; the spec half of objectui#11070 round 9). The console stopped reading the '
+      + 'authored override: the field its line grid stamps with each line\'s position on '
+      + 'drag-reorder is derived from the child object — its first field named `position`, '
+      + '`sort_order`, `sequence`, `line_no`, `line_number` or `sort` — and the pinned console had '
+      + 'crossed that change while the spec still declared the key, so an authored value published '
+      + 'green and was dropped. A retiredKey tombstone on the strict detail entry with one D2 '
+      + 'conversion that is a pure lossless DELETE scoped by component `type` and by position '
+      + '(`properties.details[]`); its D3 entry `object-master-detail-form-detail-sort-field-retired` '
+      + 'carries the one judgment left, whether the child object declares the field the line order '
+      + 'is kept in.',
+  },
   {
     id: 'object-tenancy-organization-field-retired',
     order: 34,
@@ -15251,6 +15267,39 @@ const step18: MigrationStep = {
         + 'the flag, the author has accepted creating records through the object\'s create action: '
         + '`object-kanban` offers no quick-add control.',
     },
+    // #21589 (ADR-0049 enforce-or-remove) — the D3 entry of the
+    // `object-master-detail-form-detail-sort-field-removed` family (one D3 entry
+    // per retirement family, even when D2 is lossless). Registered key:
+    // `ui/ObjectMasterDetailFormProps:details.sortField`. The strip changes
+    // nothing a user sees, because the console already ignored the authored
+    // value; what it leaves is the one judgment a delete cannot make — whether the
+    // child object carries the field the line order is kept in.
+    {
+      id: 'object-master-detail-form-detail-sort-field-retired',
+      // No backticks in `surface` — build-upgrade-guide.ts renders it inside a code
+      // span AND a table cell.
+      surface: 'page.component.object-master-detail-form.details[].sortField — a detail entry\'s '
+        + 'authored line-position field',
+      replacement: 'Nothing on the entry: delete the key. The line grid stamps each line\'s position into '
+        + 'the child object\'s own field, derived from the child object: its first field named '
+        + '`position`, `sort_order`, `sequence`, `line_no`, `line_number` or `sort`. To keep the line '
+        + 'order a drag-reorder sets, give the child object one of those fields (under the name the '
+        + 'deleted key named, when it is one of them).',
+      reason: 'The D2 conversion `object-master-detail-form-detail-sort-field-removed` deletes '
+        + '`sortField` from every `object-master-detail-form` detail entry, and the delete is lossless: '
+        + 'the console stopped reading the authored override, and the line grid stamps the field it '
+        + 'derives from the child object whatever the entry says. What the conversion cannot decide is '
+        + 'where the line order lives. An entry whose key named a field the derivation does not pick — '
+        + 'a name outside that list, or a second sort-named field after the first — saves its line '
+        + 'order into the derived field instead, or nowhere when the child object has none. An entry '
+        + 'that names `relationshipField` and at least one column and gives every column a `type` is '
+        + 'kept exactly as authored: no child schema is loaded for it, so no line position is stamped '
+        + 'and a drag-reorder is not saved, before and after the upgrade alike.',
+      acceptanceCriteria: 'No `object-master-detail-form` detail entry carries `sortField`; the props '
+        + 'lint reports one with the prescription. For each entry that had set it, the child object '
+        + 'declares the field the line order is kept in under one of the derived names, and after a '
+        + 'drag-reorder and save the lines reload in the order they were dragged into.',
+    },
     // #19054 (ADR-0049 enforce-or-remove; maintainer ruling 2026-09-18) — the D3
     // entry of the `object-tenancy-organization-field-removed` family (ruling B on
     // #17152: one D3 entry per retirement family, even when D2 is lossless). This
@@ -19925,7 +19974,7 @@ const step18: MigrationStep = {
         + 'grid columns), including `scale` on a column that declares no `type` and whose `name` is a '
         + '`currency` field of the entry\'s `childObject`',
       replacement: 'each entry is `{ childObject, relationshipField?, columns?, formFields?, '
-        + 'inlineMode?, amountField?, sortField?, totalField?, title?, minRows?, maxRows?, addLabel? }` '
+        + 'inlineMode?, amountField?, totalField?, title?, minRows?, maxRows?, addLabel? }` '
         + '— the keys the renderer reads — with `inlineMode` one of `grid` / `form`. Each column is the '
         + 'strict, name-keyed inline grid column a relationship field\'s `inlineColumns` takes — '
         + '`{ name, label?, type?, … }`, where `{ name }` alone hydrates the rest from the child '
@@ -20116,9 +20165,10 @@ const step18: MigrationStep = {
         + '`{ name, label?, type?, options?, … }`. Write `name` where a column said `field` (or '
         + '`fieldName`, `key`); declare `label`, `type` and `options` on the column, because this block '
         + 'draws a column exactly as declared and hydrates nothing from the child object\'s field; '
-        + 'delete `scale` from a column declaring `type: \'currency\'`; delete `addLabel`, `sortField`, '
-        + '`formFields` and `inlineMode`, which belong to an `object-master-detail-form` detail entry and '
-        + 'are not read here, and any other key the shape does not declare.',
+        + 'delete `scale` from a column declaring `type: \'currency\'`; delete `addLabel`, `formFields` '
+        + 'and `inlineMode`, which belong to an `object-master-detail-form` detail entry and are not read '
+        + 'here, `sortField`, which no block takes (the detail entry derives the line-position field from '
+        + 'the child object), and any other key the shape does not declare.',
       reason: 'The block draws one inline grid of the record\'s child rows, through the same objectui '
         + 'grid as the other three carriers of the inline grid column, but it had no `ComponentPropsMap` '
         + 'row: it was the one entry on the string-arm registration ledger, so the component-props gate '
@@ -24901,6 +24951,27 @@ export const RETIRED_KEYS_BY_MAJOR: Readonly<Record<number, readonly string[]>>
     // this shape; `ViewTabSchema` stays, reused by the page-only `userFilters.tabs`
     // preset bar. D2: `view-list-tabs-removed`.
     'ui/ObjectListView:tabs',
+    // #21589 — ADR-0049 enforce-or-remove through the ADR-0087 D2 route, the spec
+    // half of objectui#11070 round 9 (the direction recorded on #21220's landing
+    // and mirrored on objectui#11396 ③: tombstone plus ADR-0087). The console
+    // retired the authored override at objectui `0a3e5409f`, and the
+    // `.objectui-sha` pin `89cad75d5570` is past it: `MasterDetailDetailConfig`
+    // has no `sortField` member (`plugin-form/src/MasterDetailForm.tsx:83`), and
+    // the field the line grid stamps with each line's position is the one
+    // `deriveDetail` derives from the child object (`deriveMasterDetail.ts:540`),
+    // handed to the grid as `sort_field` (`:874`). Tombstoned with `retiredKey()`
+    // in the strict detail entry; a NESTED row (an array member, spelled without
+    // its `[]`), so it has no `authorable-surface/` line and checks (b2)/(b3)
+    // resolve it against the emitted schema. Stored and built pages are stripped
+    // by the D2 conversion `object-master-detail-form-detail-sort-field-removed`,
+    // a pure lossless delete scoped by component `type` and position; its D3
+    // record is `object-master-detail-form-detail-sort-field-retired`.
+    //
+    // Registered under 18, not 17: the removal ships on the 17.x line
+    // (launch-window convention: accept-set narrowings ride minor releases) and
+    // the prescription lives at the major boundary where `migrate meta` users
+    // look — the `ui/PageHeaderProps:breadcrumb` precedent.
+    'ui/ObjectMasterDetailFormProps:details.sortField',
     // ADR-0090 D2 (no Profile concept) + ADR-0049 enforce-or-remove; maintainer
     // ruling 2026-09-12, decision batch #121 item 2, verbatim 「同意」.
     // `Page.assignedProfiles` was an authorable key named for the concept ADR-0090 D2
diff --git a/packages/spec/src/ui/component.zod.ts b/packages/spec/src/ui/component.zod.ts
index cca8b735a74..5881437da05 100644
--- a/packages/spec/src/ui/component.zod.ts
+++ b/packages/spec/src/ui/component.zod.ts
@@ -81,6 +81,10 @@ import { SectionGroupKeySchema, sectionGroupReferenceRefinement } from '../share
 // `subforms[].columns` take, referenced rather than copied: all three carriers
 // feed one objectui grid.
 import { InlineGridColumnSchema } from '../data/field.zod';
+// [#21589] The child field names the renderer derives a detail's line-position
+// field from — the one list the retired detail-entry `sortField`'s
+// prescriptions print (reached by relative import only, never the barrel).
+import { INLINE_GRID_SORT_FIELD_LIST } from '../data/inline-grid-sort-fields';
 
 // ---------------------------------------------------------------------------
 // CLOSED AGAINST UNKNOWN KEYS as of #4001 batch A -- all 31 object sites.
@@ -2209,10 +2213,15 @@ export const RecordLineItemsProps = lazySchema(() => strictObject({
     // author moving a child collection over from `object-master-detail-form`
     // carries along. Measured at the pin: the panel hands the grid no
     // `add_label` / `sort_field` and no `onRowExpand` (`:694-710`, `:806-817`).
+    // `sortField` has since left the detail entry too (#21589, a tombstone
+    // there): the line-position field is derived from the child object and
+    // never authored, so its answer names no block that takes it.
     addLabel: '`record:line_items` does not read `addLabel`: its grid draws the built-in, localized '
       + 'Add button. `addLabel` belongs to an `object-master-detail-form` detail entry.',
     sortField: '`record:line_items` does not read `sortField`: its grid stamps no line position, so a '
-      + 'drag-reorder is not saved. `sortField` belongs to an `object-master-detail-form` detail entry.',
+      + 'drag-reorder is not saved. No block takes an authored `sortField`: an '
+      + '`object-master-detail-form` detail entry derives the line-position field from the child '
+      + `object's ${INLINE_GRID_SORT_FIELD_LIST} field.`,
     formFields: '`record:line_items` draws an editable grid only, with no per-row expand form, so it '
       + 'does not read `formFields`. It belongs to an `object-master-detail-form` detail entry.',
     inlineMode: '`record:line_items` draws an editable grid only, so it does not read `inlineMode`. It '
@@ -5815,10 +5824,12 @@ const MASTER_DETAIL_DETAIL_HISTORY =
 
 /**
  * One `object-master-detail-form` detail collection (#20928) — STRICT, and
- * exactly the twelve keys objectui's `MasterDetailForm` reads off an entry
+ * exactly the eleven keys objectui's `MasterDetailForm` reads off an entry
  * (`packages/plugin-form/src/MasterDetailForm.tsx`, its
- * `MasterDetailDetailConfig` and every `d.<key>` read in the file, read at the
- * `.objectui-sha` pin `31971ff1e28f`). A key nobody reads is not declared.
+ * `MasterDetailDetailConfig` and every `d.<key>` read in the file; read at the
+ * `.objectui-sha` pin `31971ff1e28f`, re-read at `89cad75d5570` for #21589),
+ * plus the `sortField` tombstone ({@link MASTER_DETAIL_DETAIL_SORT_FIELD_RETIRED}).
+ * A key nobody reads is not declared.
  *
  * `columns` IS {@link InlineGridColumnSchema}, the same object a relationship
  * field's `inlineColumns` and a form view's `subforms[].columns` take: the
@@ -5831,14 +5842,16 @@ const MASTER_DETAIL_DETAIL_HISTORY =
  *
  * The keys the entry shares with a form view's `subforms[]` entry take that
  * entry's types and alias table, so one concept is spelled one way on both
- * 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 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.
+ * child-collection surfaces. The two it adds are the renderer's own:
+ * `formFields` (the per-row expand form) and `inlineMode` (the two form
+ * factors a relationship field's `inlineEdit` names; absence takes the
+ * relationship's own resolution only on an entry the renderer derives, and its
+ * describe states both paths). The line-position field the grid stamps on
+ * drag-reorder is NOT a key: the renderer derives it from the child object
+ * ({@link INLINE_GRID_SORT_FIELD_LIST}), and `sortField`, the authored override
+ * it used to take, is a tombstone. `title` and `addLabel` are plain strings
+ * because the renderer draws them as a React child and a button label without
+ * resolving a locale map.
  *
  * A factory called inside {@link ObjectMasterDetailFormPropsSchema}'s own lazy
  * body, the way a form view's `subforms[]` entry is built inline in its
@@ -5846,6 +5859,41 @@ const MASTER_DETAIL_DETAIL_HISTORY =
  * nothing exports, which the schema-graph walks (`alias-integrity.test.ts`)
  * never descend into, so its alias table would go unjudged.
  */
+/**
+ * REMOVED (#21589 — ADR-0049 enforce-or-remove through the ADR-0087 D2 route;
+ * the spec half of objectui#11070 round 9, the direction recorded on #21220's
+ * landing and mirrored on objectui#11396 ③).
+ *
+ * An authored override the console no longer reads. At the `.objectui-sha` pin
+ * `89cad75d5570`, `MasterDetailDetailConfig` has no `sortField` member
+ * (`plugin-form/src/MasterDetailForm.tsx:83`): the field the line grid stamps
+ * with each line's position is DERIVED from the child object (`deriveDetail`,
+ * `deriveMasterDetail.ts:540`), carried on the resolved entry and handed to
+ * the grid as `sort_field` (`:874`). The pin crossed that change without the
+ * spec half, so an authored `sortField` published green, and a drag-reorder
+ * stamped the derived field, or none.
+ *
+ * The live mechanism is the child object's own field: its first field named
+ * one of {@link INLINE_GRID_SORT_FIELD_LIST}, on an entry the renderer
+ * resolves. An entry that names `relationshipField` and at least one column
+ * and gives every column a `type` is kept exactly as authored: the renderer
+ * loads no child schema for it, so it stamps no line position (`:977-979`).
+ *
+ * Stored and built pages that carry the key are stripped by the D2 conversion
+ * `object-master-detail-form-detail-sort-field-removed`, with a notice; its D3
+ * record is `object-master-detail-form-detail-sort-field-retired`.
+ */
+const MASTER_DETAIL_DETAIL_SORT_FIELD_RETIRED =
+  '`object-master-detail-form` property `details[].sortField` was removed in @objectstack/spec 17 '
+  + '(ADR-0087 D2) — the console reads no authored value: the field the line grid stamps with each '
+  + 'line\'s position on drag-reorder is derived from the child object, so an authored `sortField` was '
+  + 'accepted and dropped. Delete the key. For a drag-reorder to be saved, give the child object a '
+  + `field named ${INLINE_GRID_SORT_FIELD_LIST}: the renderer stamps the child's first field with one `
+  + 'of those names — except on an entry that names `relationshipField` and at least one column and '
+  + 'gives every column a `type`, which the renderer keeps exactly as authored and stamps no line '
+  + 'position on. '
+  + 'Run `os migrate meta --from 17` to list the mechanical edits for existing sources; apply them by hand.';
+
 function masterDetailDetailEntry() {
   return strictObject({
     surface: 'this `object-master-detail-form` detail entry',
@@ -5862,7 +5910,9 @@ function masterDetailDetailEntry() {
     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 and the `totalField` rollup. When omitted it is picked from the grid's number and currency columns: a computed one, else one named `amount`, `total`, `subtotal`, `line_total`, `line_amount` or `net_amount`, else the last currency column, else the last numeric one — except on an entry that names `relationshipField` and at least one column and gives every column a `type`. The renderer keeps that entry exactly as authored, so nothing is picked. With no `amountField` authored or picked, the sums read a child column named `amount`, and the grid shows a running total only when `totalField` is set"),
-    sortField: z.string().optional().describe("Child field holding the line sort position, stamped on drag-reorder. When omitted it is the child object's first field named `position`, `sort_order`, `sequence`, `line_no`, `line_number` or `sort`, if it has one — except on an entry that names `relationshipField` and at least one column and gives every column a `type`. The renderer keeps that entry exactly as authored: nothing is derived, the grid stamps no line position, and a drag-reorder is not saved"),
+    // A tombstone: the line-position field is derived from the child object,
+    // never authored — see MASTER_DETAIL_DETAIL_SORT_FIELD_RETIRED above.
+    sortField: retiredKey(MASTER_DETAIL_DETAIL_SORT_FIELD_RETIRED),
     totalField: z.string().optional().describe('Parent field to receive the rolled-up sum'),
     title: z.string().optional().describe('Section title'),
     minRows: z.number().optional().describe('Minimum number of rows'),
diff --git a/packages/spec/src/ui/master-detail-detail-sort-field-retirement.test.ts b/packages/spec/src/ui/master-detail-detail-sort-field-retirement.test.ts
new file mode 100644
index 00000000000..2d8e0b881b0
--- /dev/null
+++ b/packages/spec/src/ui/master-detail-detail-sort-field-retirement.test.ts
@@ -0,0 +1,474 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * An `object-master-detail-form` detail entry's `sortField` RETIRED (#21589) —
+ * ADR-0049 enforce-or-remove through the ADR-0087 D2 route, the spec half of
+ * objectui#11070 round 9 (the direction recorded on #21220's landing, mirrored
+ * on objectui#11396 ③).
+ *
+ * Measured before removal, at the `.objectui-sha` pin `89cad75d5570`:
+ * `MasterDetailDetailConfig` has no `sortField` member
+ * (`plugin-form/src/MasterDetailForm.tsx:83`); the field the line grid stamps
+ * with each line's position is DERIVED from the child object
+ * (`deriveMasterDetail.ts:540`) and handed to the grid as `sort_field`
+ * (`:874`). The spec still declared the key, so an authored value published
+ * green and was dropped. The writer census at the retirement is zero.
+ *
+ * Bookkeeping shapes, pinned below:
+ *   1. A `retiredKey()` tombstone on the strict detail entry — the refusal
+ *      carries the prescription, which names the derived field set from its
+ *      one declaration (`data/inline-grid-sort-fields.ts`), and the key's
+ *      input type is `never`. `PageComponentSchema.properties` is an open bag,
+ *      so the props schema is reached by the advisory props lint and never by
+ *      the page parse: an existing page is never hard-refused.
+ *   2. D2 conversion `object-master-detail-form-detail-sort-field-removed`
+ *      (step 18), a strip scoped by component type and by position, retired
+ *      from the load path: a stored or built page replays clean, with a notice.
+ *   3. `RETIRED_KEYS_BY_MAJOR[18]` carries the NESTED key
+ *      `ui/ObjectMasterDetailFormProps:details.sortField`, and the family's D3
+ *      entry is `object-master-detail-form-detail-sort-field-retired`.
+ *   4. `record:line_items`' answer to the same spelling names no block that
+ *      takes it any more.
+ *
+ * On the assertion set: a schema refusal raises a `ZodError` whose issues carry
+ * `code` and `path` but no ADR-0112 `status` — no HTTP door parses this row
+ * (the page write door parses `properties` as an open bag). So each refusal is
+ * pinned by the issue `code`, the `path` naming the key, and the prescription.
+ */
+
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+import { describe, expect, it } from 'vitest';
+import { z } from 'zod';
+
+import { collectConversionNotices } from '../conversions/apply';
+import { ALL_CONVERSIONS } from '../conversions/registry';
+import { applyConversionsToStoredItem } from '../conversions/stored';
+import type { ConversionNotice } from '../conversions/types';
+import { INLINE_GRID_SORT_FIELDS } from '../data/inline-grid-sort-fields';
+import { MIGRATIONS_BY_MAJOR, RETIRED_KEYS_BY_MAJOR } from '../migrations/registry';
+import { ComponentPropsMap, ObjectMasterDetailFormPropsSchema, RecordLineItemsProps } from './component.zod';
+import { PageSchema } from './page.zod';
+
+const CONVERSION_ID = 'object-master-detail-form-detail-sort-field-removed';
+const D3_ID = 'object-master-detail-form-detail-sort-field-retired';
+const REGISTERED_KEY = 'ui/ObjectMasterDetailFormProps:details.sortField';
+
+// Unanchored, because a thrown `ZodError`'s message is the JSON of its issues;
+// the key-first house convention is asserted on the issue message itself.
+const PRESCRIPTION =
+  /`object-master-detail-form` property `details\[\]\.sortField` was removed in @objectstack\/spec 17 \(ADR-0087 D2\) — the console reads no authored value.*Delete the key\..*Run `os migrate meta --from 17` to list the mechanical edits for existing sources; apply them by hand\./s;
+
+/** A detail entry's live keys — the showcase project workspace's entry shape. */
+const ENTRY = { title: 'Lines', childObject: 'crm_invoice_line', addLabel: 'Add line' } as const;
+
+const props = (details: unknown[]) => ({ objectName: 'crm_invoice', details });
+
+/** A stored `page` row whose block's detail entry carries `sortField`. */
+const storedPage = (sortField: string) => ({
+  name: 'invoice_entry',
+  label: 'Invoice Entry',
+  type: 'app',
+  regions: [
+    {
+      name: 'main',
+      components: [{ type: 'object-master-detail-form', properties: props([{ ...ENTRY, sortField }]) }],
+    },
+  ],
+});
+
+type Notice = Pick<ConversionNotice, 'conversionId' | 'path' | 'from' | 'to'>;
+const brief = (n: ConversionNotice): Notice => ({
+  conversionId: n.conversionId,
+  path: n.path,
+  from: n.from,
+  to: n.to,
+});
+
+describe('object-master-detail-form detail-entry sortField retirement — the tombstone', () => {
+  it('refuses the key on a detail entry, at the key, with the prescription', () => {
+    for (const value of ['line_no', 'position']) {
+      const r = ObjectMasterDetailFormPropsSchema.safeParse(props([{ ...ENTRY, sortField: value }]));
+      expect(r.success, `sortField: ${value}`).toBe(false);
+      if (r.success) continue;
+      expect(r.error.issues).toHaveLength(1);
+      const issue = r.error.issues[0]!;
+      expect(issue.code).toBe('invalid_type');
+      expect(issue.path).toEqual(['details', 0, 'sortField']);
+      expect(issue.message).toMatch(PRESCRIPTION);
+      // House convention 1: the fully-qualified key, in backticks, opens it.
+      expect(issue.message.startsWith('`object-master-detail-form` property `details[].sortField` was removed')).toBe(true);
+    }
+  });
+
+  it('the prescription names every derived sort-field name, from the one declaration', () => {
+    const r = ObjectMasterDetailFormPropsSchema.safeParse(props([{ ...ENTRY, sortField: 'line_no' }]));
+    const message = r.success ? '' : r.error.issues[0]!.message;
+    expect(INLINE_GRID_SORT_FIELDS.size).toBe(6);
+    for (const name of INLINE_GRID_SORT_FIELDS) expect(message, name).toContain(`\`${name}\``);
+  });
+
+  it('the row the props lint dispatches on is the same schema, so it refuses it too', () => {
+    // `validateComponentProps` (packages/lint) reads `ComponentPropsMap[type]`;
+    // a rebinding to some other shape would pass the pins above and still
+    // accept the key where an author meets it.
+    expect(ComponentPropsMap['object-master-detail-form']).toBe(ObjectMasterDetailFormPropsSchema);
+    expect(() => ComponentPropsMap['object-master-detail-form'].parse(props([{ ...ENTRY, sortField: 'sort' }])))
+      .toThrow(PRESCRIPTION);
+  });
+
+  it('refuses the key by the TOMBSTONE, not by the strict unknown-key arm — the two are different answers', () => {
+    const retired = ObjectMasterDetailFormPropsSchema.safeParse(props([{ ...ENTRY, sortField: 'line_no' }]));
+    expect(retired.success).toBe(false);
+    expect((retired.error?.issues ?? []).map((i) => i.code)).not.toContain('unrecognized_keys');
+    // CONTROL: an undeclared sibling on the same entry comes back as
+    // `unrecognized_keys`. Without this pair, a shape that had simply DROPPED
+    // the key would pass the pin above on the strict arm's generic message.
+    const undeclared = ObjectMasterDetailFormPropsSchema.safeParse(props([{ ...ENTRY, zzzNotAKey: 'line_no' }]));
+    expect(undeclared.success).toBe(false);
+    const issue = undeclared.error?.issues.find((i) => i.code === 'unrecognized_keys') as
+      | { keys?: string[]; path?: unknown[] }
+      | undefined;
+    expect(issue?.keys).toEqual(['zzzNotAKey']);
+    expect(issue?.path).toEqual(['details', 0]);
+  });
+
+  it('CONTROL: an entry without the key parses, keeps its live keys, and grows no `sortField`', () => {
+    const r = ObjectMasterDetailFormPropsSchema.safeParse(props([ENTRY]));
+    expect(r.success, JSON.stringify(r.error?.issues ?? [])).toBe(true);
+    if (!r.success) return;
+    const [entry] = (r.data as { details: Record<string, unknown>[] }).details;
+    expect(entry).toEqual(ENTRY);
+    expect(entry).not.toHaveProperty('sortField');
+  });
+
+  it('the walked shape keeps `sortField` as a key of the detail entry', () => {
+    type Unwrapped = { unwrap(): { element: { shape: Record<string, unknown> } } };
+    const details = (ObjectMasterDetailFormPropsSchema.shape as unknown as Record<string, Unwrapped>).details;
+    const entryKeys = Object.keys(details.unwrap().element.shape);
+    expect(entryKeys).toContain('sortField');
+    expect(entryKeys, 'CONTROL: its live neighbour').toContain('amountField');
+    // Eleven keys the renderer reads, plus the tombstone.
+    expect(entryKeys).toHaveLength(12);
+  });
+
+  it('fails tsc at the authoring site: the input type of `sortField` is `never`', () => {
+    const authored: z.input<typeof ObjectMasterDetailFormPropsSchema> = {
+      objectName: 'crm_invoice',
+      details: [
+        {
+          ...ENTRY,
+          // @ts-expect-error — `sortField` is a retiredKey() tombstone: its input type is `never`.
+          sortField: 'line_no',
+        },
+      ],
+    };
+    // The parse channel agrees with the type channel on the same literal.
+    expect(() => ObjectMasterDetailFormPropsSchema.parse(authored)).toThrow(PRESCRIPTION);
+  });
+
+  it('never hard-refuses an existing page: the page parse still accepts a block carrying the key', () => {
+    // `PageComponentSchema.properties` is an open bag — the page door does not
+    // dispatch on the component type; the tombstone speaks through the props lint.
+    const r = PageSchema.safeParse(storedPage('line_no'));
+    expect(r.success, JSON.stringify(r.error?.issues ?? [])).toBe(true);
+  });
+
+  it('`record:line_items` answers the same spelling naming no block that takes it', () => {
+    const r = RecordLineItemsProps.safeParse({
+      childObject: 'crm_invoice_line',
+      relationshipField: 'invoice',
+      columns: [{ name: 'quantity' }],
+      sortField: 'line_no',
+    });
+    expect(r.success).toBe(false);
+    const issue = r.error?.issues.find((i) => i.code === 'unrecognized_keys');
+    expect(issue?.path).toEqual([]);
+    expect(issue?.message).toContain('No block takes an authored `sortField`');
+    // CONTROL: the sibling entry key still names the block that takes it.
+    const addLabel = RecordLineItemsProps.safeParse({
+      childObject: 'crm_invoice_line',
+      relationshipField: 'invoice',
+      columns: [{ name: 'quantity' }],
+      addLabel: 'Add line',
+    });
+    expect(addLabel.error?.issues.find((i) => i.code === 'unrecognized_keys')?.message)
+      .toContain('`addLabel` belongs to an `object-master-detail-form` detail entry');
+  });
+});
+
+describe('object-master-detail-form detail-entry sortField retirement — the D2 conversion', () => {
+  it('a STORED page whose detail entry carries the key loads with it stripped and the notice recorded', () => {
+    const notices: ConversionNotice[] = [];
+    const row = storedPage('line_no');
+    const rehydrated = applyConversionsToStoredItem('page', row, {
+      onNotice: (n) => notices.push(n),
+    }) as ReturnType<typeof storedPage>;
+
+    expect(notices.map(brief)).toEqual([
+      {
+        conversionId: CONVERSION_ID,
+        path: 'pages[0].regions[0].components[0].properties.details[0].sortField',
+        from: 'sortField',
+        to: '(removed)',
+      },
+    ]);
+    const properties = rehydrated.regions[0]!.components[0]!.properties;
+    // Every live key on the same entry and block survives byte-for-byte.
+    expect(properties).toEqual(props([ENTRY]));
+    // The rehydrated block is exactly what the props row accepts now, and the
+    // page still parses.
+    expect(ObjectMasterDetailFormPropsSchema.safeParse(properties).success).toBe(true);
+    expect(PageSchema.safeParse(rehydrated).success).toBe(true);
+  });
+
+  it('a BUILT artifact replays the same strip — every position the block can sit in, every entry', () => {
+    const artifact = {
+      pages: [
+        {
+          name: 'invoice_entry',
+          regions: [
+            {
+              name: 'main',
+              components: [
+                {
+                  type: 'object-master-detail-form',
+                  properties: props([{ ...ENTRY, sortField: 'line_no' }, { childObject: 'crm_payment' }, { childObject: 'crm_step', sortField: 'position' }]),
+                },
+                {
+                  type: 'page:card',
+                  properties: {
+                    children: [{ type: 'object-master-detail-form', properties: props([{ ...ENTRY, sortField: 'sequence' }]) }],
+                  },
+                },
+              ],
+            },
+          ],
+        },
+        {
+          name: 'invoice_entry_detail',
+          kind: 'slotted',
+          regions: [],
+          slots: { details: { type: 'object-master-detail-form', properties: props([{ ...ENTRY, sortField: 'sort' }]) } },
+        },
+      ],
+    };
+    const { stack, notices } = collectConversionNotices(artifact, { includeRetired: true });
+    expect(notices.filter((n) => n.conversionId === CONVERSION_ID).map((n) => n.path)).toEqual([
+      'pages[0].regions[0].components[0].properties.details[0].sortField',
+      'pages[0].regions[0].components[0].properties.details[2].sortField',
+      'pages[0].regions[0].components[1].properties.children[0].properties.details[0].sortField',
+      'pages[1].slots.details.properties.details[0].sortField',
+    ]);
+    expect(JSON.stringify(stack)).not.toContain('"sortField"');
+  });
+
+  it('CONTROL: a block whose entries carry no key is unchanged — no notice, and the row comes back by reference', () => {
+    const row = {
+      name: 'invoice_entry',
+      regions: [{ name: 'main', components: [{ type: 'object-master-detail-form', properties: props([ENTRY]) }] }],
+    };
+    const notices: ConversionNotice[] = [];
+    const rehydrated = applyConversionsToStoredItem('page', row, { onNotice: (n) => notices.push(n) });
+    expect(notices.filter((n) => n.conversionId === CONVERSION_ID)).toHaveLength(0);
+    expect(rehydrated).toBe(row);
+  });
+
+  it('is scoped by component TYPE and POSITION: the same key elsewhere is not this entry\'s', () => {
+    const artifact = {
+      pages: [
+        {
+          name: 'p',
+          regions: [
+            {
+              name: 'main',
+              components: [
+                // Another component's own `details[].sortField`.
+                { type: 'acme:line_editor', properties: { details: [{ sortField: 'position' }] } },
+                // The block's TOP-level props: not a detail entry, so not this
+                // key (the props gate reports it as an unknown key).
+                { type: 'object-master-detail-form', properties: { objectName: 'crm_invoice', sortField: 'position' } },
+              ],
+            },
+          ],
+        },
+      ],
+    };
+    const { stack, notices } = collectConversionNotices(artifact, { includeRetired: true });
+    expect(notices.filter((n) => n.conversionId === CONVERSION_ID)).toHaveLength(0);
+    expect(stack).toBe(artifact);
+  });
+
+  it('is idempotent by construction: a second replay converts nothing', () => {
+    const { stack } = collectConversionNotices({ pages: [storedPage('line_no')] }, { includeRetired: true });
+    const replay = collectConversionNotices(stack, { includeRetired: true });
+    expect(replay.notices).toHaveLength(0);
+    expect(replay.stack).toBe(stack);
+  });
+
+  it('is retired from the load path — the authoring funnel does not rewrite a live source', () => {
+    const input = { pages: [storedPage('line_no')] };
+    const { stack, notices } = collectConversionNotices(input);
+    expect(notices.filter((n) => n.conversionId === CONVERSION_ID)).toHaveLength(0);
+    expect(stack).toEqual(input);
+  });
+});
+
+describe('object-master-detail-form detail-entry sortField retirement — the ADR-0087 ledger row', () => {
+  it('declares ONE nested key under major 18', () => {
+    expect(RETIRED_KEYS_BY_MAJOR[18]).toContain(REGISTERED_KEY);
+    const all = Object.values(RETIRED_KEYS_BY_MAJOR).flat();
+    expect(all.filter((k) => k.startsWith('ui/ObjectMasterDetailFormProps:'))).toEqual([REGISTERED_KEY]);
+  });
+
+  it('wires the D2 conversion into the step-18 chain as a retired, stamped, lossless strip', () => {
+    expect(MIGRATIONS_BY_MAJOR[18]!.conversionIds).toContain(CONVERSION_ID);
+    const conversion = ALL_CONVERSIONS.find((c) => c.id === CONVERSION_ID);
+    expect(conversion, 'the D2 conversion must be registered').toBeDefined();
+    expect(conversion!.toMajor).toBe(18);
+    expect(conversion!.retiredFromLoadPath).toBe(true);
+    expect(conversion!.retiredAfter).toMatch(/^\d+\.\d+\.\d+$/);
+    expect(conversion!.surface).toBe('page.component.object-master-detail-form.details[].sortField');
+  });
+
+  it('carries ONE D3 entry for the family, naming its D2 conversion', () => {
+    const entries = MIGRATIONS_BY_MAJOR[18]!.semantic.filter((s) => s.id === D3_ID);
+    expect(entries, 'the family needs its own D3 entry').toHaveLength(1);
+    const [entry] = entries;
+    expect(entry!.reason).toContain(`\`${CONVERSION_ID}\``);
+    expect(entry!.replacement).toContain('delete the key');
+    // The D3 text is concatenated into the generated registry as a literal, so
+    // it cannot import the one declaration; this keeps the two lists equal.
+    for (const name of INLINE_GRID_SORT_FIELDS) expect(entry!.replacement, name).toContain(`\`${name}\``);
+    expect(entry!.acceptanceCriteria.length).toBeGreaterThan(0);
+  });
+});
+
+// ─── Tree-scoped absence, inside the radius the package already declares ───
+//
+// `tsc` sweeps only TYPED authoring sites, and a page component's `properties`
+// is an open bag, so `tsc` does not reach a block authored through
+// `definePage`/`defineStack` at all. This walk covers every text file under the
+// five repo roots `scripts/cross-package-test-inputs.mjs` declares for
+// `@objectstack/spec#test` (mirrored in `turbo.json`), plus the example apps'
+// own `src/` trees.
+//
+// The matcher judges the AUTHORING SHAPE, never a mention: `sortField` in key
+// position with a snake_case field-name value, quoted or bare (TS / JS / JSON,
+// and YAML). A guidance or prescription string, a schema declaration and the
+// grid's own `sort_field` never take that shape. Prose mentions are spelled in
+// inline code in this repo, and inline code is stripped before judging. The
+// bound, stated: a value that is not a field-name literal, a shorthand
+// property, and `docs/**`, `.claude/**`, `.github/**` and the repo-root files
+// are outside what this walk sees. A future schema that declares a `sortField`
+// of its own would trip this walk: narrow the matcher to detail entries then,
+// never exclude the new file.
+describe('tree-scoped absence: nothing inside the declared radius still authors a detail-entry sortField', () => {
+  const SPEC_ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '../..');
+  const REPO_ROOT = path.resolve(SPEC_ROOT, '../..');
+  const THIS_FILE = path.relative(REPO_ROOT, fileURLToPath(import.meta.url)).split(path.sep).join('/');
+
+  /** The walked roots — declared in `scripts/cross-package-test-inputs.mjs` under `@objectstack/spec`. */
+  const WALK_ROOTS = ['packages', 'examples', 'skills', 'content', 'scripts'];
+  const SCANNED_EXT = new Set(['.ts', '.mts', '.cts', '.js', '.mjs', '.cjs', '.json', '.md', '.mdx', '.yaml', '.yml']);
+  /** Under `examples/` the non-code extensions, plus `.ts` inside an app's own `src/` tree. */
+  const EXAMPLES_EXT = new Set(['.json', '.md', '.mdx', '.yaml', '.yml']);
+  const EXAMPLE_APP_SRC_TS = /^examples\/[^/]+\/src\/.+\.ts$/;
+  const SKIPPED_DIRS = new Set(['node_modules', 'dist', '.git', '.turbo', '.cache', '.objectstack', 'coverage', '.next', '.source']);
+
+  const AUTHORING = /(^|[^\w.$])["']?sortField["']?[ \t]*:[ \t]*(["']?)[a-z_][a-z0-9_]*\2(?=[ \t]*([,}\]#]|$))/m;
+
+  /** Inline code spans are prose; newline-bounded, so a fenced example is still judged. */
+  const stripInlineCode = (text: string): string => text.replace(/`[^`\n]*`/g, '');
+  const judge = (text: string): RegExpExecArray | null => AUTHORING.exec(stripInlineCode(text));
+
+  /**
+   * Structural exclusions — the retirement kit, each with its reason. ⛔ NOT an
+   * allowlist file (`spec-property-retirement` §4): every entry's JOB is to
+   * spell the retired key.
+   */
+  const EXCLUDED = new Set([
+    // This pin authors the key to assert its refusal and its conversion.
+    THIS_FILE,
+    // The props-lint pin authors the key to assert the advisory warning an
+    // author meets at `os validate` / `os build` / `os lint`.
+    'packages/lint/src/validate-component-props.test.ts',
+  ]);
+  const EXCLUDED_PREFIXES = [
+    // The D2 conversion's fixture authors the pre-retirement entry on purpose.
+    'packages/spec/src/conversions/',
+    // Release-owned prose records the removal; never edited by a code PR.
+    'content/docs/releases/',
+    // GITIGNORED build output (`packages/spec/json-schema/`), reached only
+    // because this is a FILESYSTEM walk. Its source is `component.zod.ts`.
+    'packages/spec/json-schema/',
+  ];
+  /** tsup's own bundle of `tsup.config.ts`, written and deleted mid-build. */
+  const TSUP_BUNDLED_CONFIG = /\.bundled_[^./]+\.mjs$/;
+
+  /** Tolerates ONLY a path that vanished mid-walk; every other read fault is re-raised. */
+  const readIfPresent = (full: string): string | undefined => {
+    try {
+      return fs.readFileSync(full, 'utf-8');
+    } catch (err) {
+      if ((err as NodeJS.ErrnoException)?.code !== 'ENOENT') throw err;
+      return undefined;
+    }
+  };
+
+  it('the matcher recognises an authoring and ignores a prose mention, a guidance string and a declaration (anti-vacuity)', () => {
+    // Offenders — the retired shape, in each syntax the walk reads.
+    expect(judge("details: [{ childObject: 'crm_invoice_line', sortField: 'line_no' }],")).not.toBeNull();
+    expect(judge("      {\n        sortField: 'position',\n      },")).not.toBeNull();
+    expect(judge('{ "details": [{ "childObject": "crm_invoice_line", "sortField": "sequence" }] }')).not.toBeNull();
+    expect(judge('      details:\n        - childObject: crm_invoice_line\n          sortField: sort\n')).not.toBeNull();
+    expect(judge("Prose.\n\n```ts\ndefinePage({ regions: [{ components: [{ properties: { details: [{ sortField: 'line_no' }] } }] }] });\n```\n")).not.toBeNull();
+    // Neighbours that must NOT match.
+    expect(judge("an authored `sortField: 'line_no'` was accepted and dropped")).toBeNull();
+    expect(judge("sortField: '`record:line_items` does not read `sortField`: its grid stamps no line position'")).toBeNull();
+    expect(judge('sortField: retiredKey(MASTER_DETAIL_DETAIL_SORT_FIELD_RETIRED),')).toBeNull();
+    expect(judge("sortField: z.string().optional().describe('Child field'),")).toBeNull();
+    expect(judge('sortField: derived.sortField,')).toBeNull();
+    expect(judge("sort_field: entry.sortField,\n  sortFields: ['name'],")).toBeNull();
+    expect(judge('"ui/ObjectMasterDetailFormProps:details.sortField",')).toBeNull();
+  });
+
+  it('no detail-entry sortField authoring survives inside the declared radius outside the retirement kit', () => {
+    const offenders: string[] = [];
+    let visited = 0;
+    let exampleSources = 0;
+    const walk = (dir: string) => {
+      for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+        const full = path.join(dir, entry.name);
+        const rel = path.relative(REPO_ROOT, full).split(path.sep).join('/');
+        if (entry.isDirectory()) {
+          if (SKIPPED_DIRS.has(entry.name) || entry.name.startsWith('.')) continue;
+          walk(full);
+          continue;
+        }
+        if (!entry.isFile()) continue;
+        const ext = path.extname(entry.name);
+        const scanned = rel.startsWith('examples/')
+          ? EXAMPLES_EXT.has(ext) || EXAMPLE_APP_SRC_TS.test(rel)
+          : SCANNED_EXT.has(ext);
+        if (!scanned) continue;
+        if (entry.name === 'CHANGELOG.md') continue; // release prose records the removal
+        if (EXCLUDED.has(rel) || EXCLUDED_PREFIXES.some((p) => rel.startsWith(p))) continue;
+        if (TSUP_BUNDLED_CONFIG.test(entry.name)) continue;
+        visited += 1;
+        if (EXAMPLE_APP_SRC_TS.test(rel)) exampleSources += 1;
+        const text = readIfPresent(full);
+        if (text === undefined) continue;
+        const m = judge(text);
+        if (m) offenders.push(`${rel} authors \`${m[0].trim().replace(/\s+/g, ' ')}\``);
+      }
+    };
+    for (const root of WALK_ROOTS) walk(path.join(REPO_ROOT, root));
+    // Anti-vacuity: the walk really covered the tree and the example apps' sources.
+    expect(visited).toBeGreaterThan(1000);
+    expect(exampleSources).toBeGreaterThan(50);
+    expect(offenders, 'a detail-entry sortField authoring means the retirement is being undone').toEqual([]);
+  });
+});
diff --git a/packages/spec/vitest.repo-tests.json b/packages/spec/vitest.repo-tests.json
index 7392a247e8c..757a6c1e324 100644
--- a/packages/spec/vitest.repo-tests.json
+++ b/packages/spec/vitest.repo-tests.json
@@ -47,6 +47,7 @@
   "src/ui/action-requires-confirmation-docblock.pin.test.ts",
   "src/ui/element-text-variant-heading-retirement.test.ts",
   "src/ui/form-field-public-picker-retirement.test.ts",
+  "src/ui/master-detail-detail-sort-field-retirement.test.ts",
   "src/ui/object-grid-resizable-columns-retirement.test.ts",
   "src/ui/page-header-breadcrumb-retirement.test.ts",
   "src/ui/view-item-owner-hidden-retirement.test.ts",