@@ -0,0 +1,22 @@
+---
+'@objectstack/spec': minor
+'@objectstack/objectql': minor
+'@objectstack/skills': minor
+'@object-ui/app-shell': minor
+'@object-ui/i18n': minor
+---
+
+fix(spec): a count roll-up saves without `summaryOperations.field`
+
+Clause-②: yes (widening)
+Metadata-protocol: added
+Skills-docs: updated here — `skills/objectstack-data/rules/field-types.md` spells `field?` in the `summary` config row, with "(omit for `count`)"; the same file's `sum` example drops its now-duplicate "ignored for count" comment, so the file's size is unchanged.
+
+The description of `summaryOperations.field` always said it is ignored for `count`, yet the schema required it for every function, so a count roll-up with no child field was refused (`422 INVALID_METADATA` at `fields.<name>.summaryOperations.field`, "expected string") and Studio's author had to pick an arbitrary child field to save one. The schema now follows its own description:
+
+- **`count` may omit `field`.** A count counts the matching child rows and reads no field, so `{ object, function: 'count' }` parses and saves as written. A count that carries a `field` is still accepted, and the field is still ignored.
+- **Every other function still needs it.** `sum`, `min`, `max` and `avg` without `field` are refused at `summaryOperations.field`, and the message names the function and the fix: name the child field to aggregate, or use `function: 'count'`.
+- **One rule, read twice.** `summaryFunctionReadsField(fn)` (exported from `@objectstack/spec/data`) is where "does this function read a child field" is written. The schema's refusal reads it, and Studio's roll-up editor reads it: for a count the editor offers no "Child field to aggregate" control, only a note that a count needs none, and saves the roll-up without `field`.
+- **The engine counts it.** The roll-up index carries no source field for such a count (`SummaryDescriptor.sourceField` is now optional), and the recompute and bulk-insert paths count child rows without reading one, as they already did for every count.
+- **Published JSON Schema.** `summaryOperations.field` is no longer in `required`; the "required unless `count`" rule is a refinement the JSON Schema does not state, so `summaryOperations` joins the dropped-refinements ledger at each schema that embeds a field.
+- **Metadata forms.** The `field` sub-row of the roll-up composite (field editor and object quick-add grid) is no longer marked required; its help text, "ignored for count", is unchanged.
@@ -712,7 +712,7 @@ Roll-up summary from child records.
 | Property | Type | Default | Description |
 |:---|:---|:---|:---|
 | `summaryOperations.object` | `string` | **required** | Child object to aggregate |
-| `summaryOperations.field` | `string` | **required** | Child field to aggregate; ignored for `count` |
+| `summaryOperations.field` | `string` | **required** for `sum`, `avg`, `min`, `max` | Child field to aggregate; a `count` counts the child rows and reads no field, so it may omit it |
 | `summaryOperations.function` | `enum` | **required** | `count`, `sum`, `avg`, `min`, or `max` |
 | `summaryOperations.relationshipField` | `string` | auto | Child FK back to the parent when it cannot be inferred |
 | `summaryOperations.filter` | `FilterCondition` | — | Only child rows matching this `where` predicate are aggregated |
@@ -729,7 +729,6 @@ currencies would be added into one number. A `count` is served
   type: 'summary',
   summaryOperations: {
     object: 'task',
-    field: 'id',
     function: 'count',
     relationshipField: 'project',
   },
 
@@ -87,7 +87,7 @@ const result = CurrencyConfigSchema.parse(data);
 | **allowCreate** | `boolean` | optional | Allow inline quick-create from the record picker: when no match exists the user can create a record from the typed text (optimistic dataSource.create with the display field). Best for simple objects whose only required field is the display field. |
 | **expression** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | CEL expression the field's value is computed from, e.g. F`record.amount * 0.1`. On a `formula` field: computed on read, no column. On any other (stored) field: computed by the engine from the row the write stores and stored, so a client-sent value never stands and a `summary` can roll the column up — on every insert and every update by id (the stored row merged with the patch), and on a predicate update only when the patch moves an input (one value for every matched row, else the update is refused). |
 | **returnType** | `Enum<'number' \| 'text' \| 'boolean' \| 'date' \| 'currency'>` | optional | Inferred value type of a formula field (number/text/boolean/date/currency). `currency`: an amount of money, in the currency the formula's own `currencyConfig` declares, as a currency field declares it (no `currencyConfig`: dynamic, the tenant default currency). |
-| **summaryOperations** | `{ object: string; field: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
+| **summaryOperations** | `{ object: string; field?: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
 | **language** | `string` | optional | Programming language for syntax highlighting (e.g., javascript, python, sql) |
 | **step** | `number` | optional | Step increment for slider (default: 1) |
 | **currencyConfig** | `{ currencyMode?: Enum<'dynamic' \| 'fixed' \| 'record'>; defaultCurrency?: string; currencyField?: string }` | optional | Which currency an amount is in: for a currency field, and for a formula field whose returnType is currency. Absent: dynamic mode. |
@@ -228,7 +228,7 @@ const result = CurrencyConfigSchema.parse(data);
 | Property | Type | Required | Description |
 | :--- | :--- | :--- | :--- |
 | **object** | `string` | ✅ | Source child object name for roll-up |
-| **field** | `string` | ✅ | Field on child object to aggregate (ignored for count) |
+| **field** | `string` | optional | Field on the child object to aggregate. Required for sum, min, max and avg; count counts the child rows and reads no field, so a count may omit it (ignored when given). |
 | **function** | `Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>` | ✅ | Aggregation function to apply |
 | **relationshipField** | `string` | optional | FK field on the child pointing back to this parent. Auto-detected from the child's lookup/master_detail field referencing this object when omitted; set explicitly only when the child has more than one such reference. |
 | **filter** | `any` | optional | Predicate restricting which child rows are aggregated (a query `where` FilterCondition, e.g. `{ status: 'received' }` or `{ type: { $in: ['signup','trial'] } }`). Omit to aggregate all children. Lets one child object feed multiple filtered roll-ups. |
 
@@ -265,7 +265,7 @@ const result = ApiMethod.parse(data);
 | **allowCreate** | `boolean` | optional | Allow inline quick-create from the record picker: when no match exists the user can create a record from the typed text (optimistic dataSource.create with the display field). Best for simple objects whose only required field is the display field. |
 | **expression** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | CEL expression the field's value is computed from, e.g. F`record.amount * 0.1`. On a `formula` field: computed on read, no column. On any other (stored) field: computed by the engine from the row the write stores and stored, so a client-sent value never stands and a `summary` can roll the column up — on every insert and every update by id (the stored row merged with the patch), and on a predicate update only when the patch moves an input (one value for every matched row, else the update is refused). |
 | **returnType** | `Enum<'number' \| 'text' \| 'boolean' \| 'date' \| 'currency'>` | optional | Inferred value type of a formula field (number/text/boolean/date/currency). `currency`: an amount of money, in the currency the formula's own `currencyConfig` declares, as a currency field declares it (no `currencyConfig`: dynamic, the tenant default currency). |
-| **summaryOperations** | `{ object: string; field: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
+| **summaryOperations** | `{ object: string; field?: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
 | **language** | `string` | optional | Programming language for syntax highlighting (e.g., javascript, python, sql) |
 | **step** | `number` | optional | Step increment for slider (default: 1) |
 | **currencyConfig** | `{ currencyMode?: Enum<'dynamic' \| 'fixed' \| 'record'>; defaultCurrency?: string; currencyField?: string }` | optional | Which currency an amount is in: for a currency field, and for a formula field whose returnType is currency. Absent: dynamic mode. |
@@ -628,7 +628,7 @@ const result = ApiMethod.parse(data);
 | **allowCreate** | `boolean` | optional | Allow inline quick-create from the record picker: when no match exists the user can create a record from the typed text (optimistic dataSource.create with the display field). Best for simple objects whose only required field is the display field. |
 | **expression** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | CEL expression the field's value is computed from, e.g. F`record.amount * 0.1`. On a `formula` field: computed on read, no column. On any other (stored) field: computed by the engine from the row the write stores and stored, so a client-sent value never stands and a `summary` can roll the column up — on every insert and every update by id (the stored row merged with the patch), and on a predicate update only when the patch moves an input (one value for every matched row, else the update is refused). |
 | **returnType** | `Enum<'number' \| 'text' \| 'boolean' \| 'date' \| 'currency'>` | optional | Inferred value type of a formula field (number/text/boolean/date/currency). `currency`: an amount of money, in the currency the formula's own `currencyConfig` declares, as a currency field declares it (no `currencyConfig`: dynamic, the tenant default currency). |
-| **summaryOperations** | `{ object: string; field: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
+| **summaryOperations** | `{ object: string; field?: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
 | **language** | `string` | optional | Programming language for syntax highlighting (e.g., javascript, python, sql) |
 | **step** | `number` | optional | Step increment for slider (default: 1) |
 | **currencyConfig** | `{ currencyMode?: Enum<'dynamic' \| 'fixed' \| 'record'>; defaultCurrency?: string; currencyField?: string }` | optional | Which currency an amount is in: for a currency field, and for a formula field whose returnType is currency. Absent: dynamic mode. |
 
@@ -99,7 +99,7 @@ Add a new field to an existing object
 | **allowCreate** | `boolean` | optional | Allow inline quick-create from the record picker: when no match exists the user can create a record from the typed text (optimistic dataSource.create with the display field). Best for simple objects whose only required field is the display field. |
 | **expression** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | CEL expression the field's value is computed from, e.g. F`record.amount * 0.1`. On a `formula` field: computed on read, no column. On any other (stored) field: computed by the engine from the row the write stores and stored, so a client-sent value never stands and a `summary` can roll the column up — on every insert and every update by id (the stored row merged with the patch), and on a predicate update only when the patch moves an input (one value for every matched row, else the update is refused). |
 | **returnType** | `Enum<'number' \| 'text' \| 'boolean' \| 'date' \| 'currency'>` | optional | Inferred value type of a formula field (number/text/boolean/date/currency). `currency`: an amount of money, in the currency the formula's own `currencyConfig` declares, as a currency field declares it (no `currencyConfig`: dynamic, the tenant default currency). |
-| **summaryOperations** | `{ object: string; field: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
+| **summaryOperations** | `{ object: string; field?: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
 | **language** | `string` | optional | Programming language for syntax highlighting (e.g., javascript, python, sql) |
 | **step** | `number` | optional | Step increment for slider (default: 1) |
 | **currencyConfig** | `{ currencyMode?: Enum<'dynamic' \| 'fixed' \| 'record'>; defaultCurrency?: string; currencyField?: string }` | optional | Which currency an amount is in: for a currency field, and for a formula field whose returnType is currency. Absent: dynamic mode. |
@@ -530,7 +530,7 @@ Add a new field to an existing object
 | **allowCreate** | `boolean` | optional | Allow inline quick-create from the record picker: when no match exists the user can create a record from the typed text (optimistic dataSource.create with the display field). Best for simple objects whose only required field is the display field. |
 | **expression** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | CEL expression the field's value is computed from, e.g. F`record.amount * 0.1`. On a `formula` field: computed on read, no column. On any other (stored) field: computed by the engine from the row the write stores and stored, so a client-sent value never stands and a `summary` can roll the column up — on every insert and every update by id (the stored row merged with the patch), and on a predicate update only when the patch moves an input (one value for every matched row, else the update is refused). |
 | **returnType** | `Enum<'number' \| 'text' \| 'boolean' \| 'date' \| 'currency'>` | optional | Inferred value type of a formula field (number/text/boolean/date/currency). `currency`: an amount of money, in the currency the formula's own `currencyConfig` declares, as a currency field declares it (no `currencyConfig`: dynamic, the tenant default currency). |
-| **summaryOperations** | `{ object: string; field: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
+| **summaryOperations** | `{ object: string; field?: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | Roll-up summary definition. The engine recomputes the value when child records are inserted/updated/deleted. |
 | **language** | `string` | optional | Programming language for syntax highlighting (e.g., javascript, python, sql) |
 | **step** | `number` | optional | Step increment for slider (default: 1) |
 | **currencyConfig** | `{ currencyMode?: Enum<'dynamic' \| 'fixed' \| 'record'>; defaultCurrency?: string; currencyField?: string }` | optional | Which currency an amount is in: for a currency field, and for a formula field whose returnType is currency. Absent: dynamic mode. |
 
@@ -618,7 +618,7 @@ Sort field and direction pair
 | **maxLength** | `integer` | optional | Maximum character count — the control's ceiling (a textarea also draws its counter) |
 | **pattern** | `string` | optional | Regular expression the value must match, as a string — the native control's `pattern`, enforced by the browser at submit |
 | **returnType** | `Enum<'number' \| 'text' \| 'boolean' \| 'date' \| 'currency'>` | optional | The value type a formula field displays (number / text / boolean / date / currency) |
-| **summaryOperations** | `{ object: string; field: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | The roll-up a summary field displays — the object field's own `{ object, field, function, … }` |
+| **summaryOperations** | `{ object: string; field?: string; function: Enum<'count' \| 'sum' \| 'min' \| 'max' \| 'avg'>; relationshipField?: string; … }` | optional | The roll-up a summary field displays — the object field's own `{ object, field, function, … }` |
 | **columns** | `{ name: string; label?: string; type?: Enum<'text' \| 'number' \| 'currency' \| 'date' \| 'datetime' \| 'time' \| 'select' \| 'lookup' \| 'file'>; width?: number; … }[]` | optional | The columns of a `grid` field — the strict, name-keyed inline grid column a relationship field's `inlineColumns` takes |
 | **minRows** | `number` | optional | A `grid` field's minimum row count: its Remove action is disabled at this many rows (no minimum when unset). Read only by the `grid` widget |
 | **maxRows** | `number` | optional | A `grid` field's maximum row count: its Add and Duplicate actions are disabled, and no blank entry row is drawn, at this many rows (no maximum when unset). Read only by the `grid` widget |
 
@@ -39,8 +39,12 @@ export interface SummaryDescriptor {
   /** FK field on the child pointing back to the parent. */
   fkField: string;
   fn: 'count' | 'sum' | 'min' | 'max' | 'avg';
-  /** Child field aggregated (unused for count). */
-  sourceField: string;
+  /**
+   * Child field aggregated — `summaryOperations.field`. Absent on a `count`,
+   * which counts the child rows and reads no field (the spec's
+   * `summaryFunctionReadsField`); every other function carries one.
+   */
+  sourceField?: string;
   /**
    * Optional predicate (a query `where` FilterCondition) restricting which child
    * rows are aggregated. ANDed with the parent-FK match when the aggregate runs.
 
@@ -62,6 +62,13 @@ describe('[#25579] createBatchSummaryAccumulator — per roll-up kind', () => {
     expect(acc.overlay(bound({ id: 'o1', lowest: null, highest: null }))!.order!.row).toEqual({ id: 'o1', lowest: 3, highest: 7 });
   });
 
+  it('[#27462] count with no sourceField (a count reads no child field): each admitted row still adds one', () => {
+    const acc = createBatchSummaryAccumulator([desc({ summaryField: 'lines', fn: 'count', sourceField: undefined })], CHILD_FIELDS)!;
+    acc.accept({ order: 'o1', amount: 5 });
+    acc.accept({ order: 'o1' });
+    expect(acc.overlay(bound({ id: 'o1', lines: 1 }))!.order!.row).toEqual({ id: 'o1', lines: 3 });
+  });
+
   it('a row never accepted moves nothing: the caller accepts only the rows its rules admitted', () => {
     const acc = createBatchSummaryAccumulator([desc({ summaryField: 'primaries', fn: 'count' })], CHILD_FIELDS)!;
     const stored = bound({ id: 'o1', primaries: 0 });