EPBDS-17018: a useForm table row starts with its values, and a submit sends every row with its edits

CLAUDE.md

@@ -136,6 +136,24 @@ whose `showIf` reads the form hears the other forms of its document tree too, wh
 what the form held before, and the tree keeps its latest tells, so a node catches up as it commits with those made
 after it rendered.
 
+Every such decision reads the merge of its tree's forms, which the tree's nodes share while what the page's forms hold
+stays the same (`keptRawFormsData`, since 2026-10-26): `formsStorage` counts each form that registers, goes or
+registers again, and a form a document renders counts its new values before the first of its subscribers hears of them
+(`createBatchedForm`). A tree's tells come too late for that: the form layer subscribes as the form commits, after the
+nodes under it. A change written into a form's values in place, which final-form tells nobody of, must be counted
+where it is made (`countFormsChange`), as the `submit` action's is. A `useForm` row's form holds its row at the row's
+place, as its fields read it (`engine/Data.tsx`), and every merge of the forms takes from it the values of the fields
+it changed and nothing else, each read and written at the field's name (`rowPlaceOf`, `changedInside`, `writeField`,
+`engine/formData.ts`). It changed a field whose value is not its start: its `initialValues`, moved, field by field, to
+what the forms holding the document from its root hold of its values after a submit (`restartWrittenRows`, which the
+`submit` action calls as it writes; a submit a row's own document makes writes into the row's form, and moves no
+start). The rest of the row, a field its cells only show included, is what the document's form holds: what another
+form, such as the row's expanded content's, has edited there, and what a submit has written of the row's form. A
+new write of a row's values into the document's form must move the start the same way. Its fields are every one it
+has registered, the ones a `showIf` hid included (`fieldNamesOf` in `createBatchedForm`). A name that comes is no
+change of what the forms hold: the kept merge is checked against the values of the names that came
+(`fieldNamesCount`, `holdsFields`), so a burst of registrations, a mount's among them, merges nothing more.
+
 A mount has a cost besides renders: every field registers with final-form. Until 2026-10-13, each registration
 published the state of every field before it and, once validation ran, validated them all, and each unregistration
 did the same. A burst of n fields cost about n²/2 of each, on the first render, a tab switch, a `showIf` that flips

src/core/engine/Data.tsx

@@ -1,6 +1,9 @@
-import React from 'react'
+import React, { useMemo } from 'react'
+import { setIn } from 'final-form'
 import { Active } from '../utils'
+import { isObject } from '../utils/object'
 import DocumentWithOwnForm from './rules'
+import { rowPlaceOf } from './formData'
 import LocalDraftTableRow from './components/LocalDraftTableRow'
 import type { LocalDraftTableRowProps } from './components/LocalDraftTableRow'
 
@@ -24,8 +27,11 @@ export type DataMeta = { view?: string, meta?: DataMeta, [key: string]: unknown
 export type DataProps = {
   /** Data of the same `kind` are grouped into an array, and validated together as a group. */
   kind: string
-  /** The UI Render instance containing this Data component; a draft row reads its data kinds */
-  instance: NonNullable<LocalDraftTableRowProps['parentInstance']>
+  /**
+   * The UI Render instance containing this Data component; a draft row reads its data kinds. None for a node rendered
+   * outside a document's render: a table's `extraItems`, a tooltip's `children`, an input's `icon`, a `values` renderer.
+   */
+  instance?: LocalDraftTableRowProps['parentInstance']
   /** The index of this Data component in the array of rendered data, for removing itself */
   index?: number | string
   /** Data.json to use */
@@ -91,6 +97,16 @@ export default function Data ({
     ? {...metaIn, relativePath, relativeIndex}
     : metaIn
 
+  // A table row that `useForm` gives a form of its own names its fields by the row's place, `dataKind.items[1].kind`
+  // (`mapper.tsx`), so its form starts from the row's values there, placed as final-form places a field's value. Until
+  // 2026-10-26 it started from them at the root of its values, where none of its fields reads: every field of the row
+  // started empty. A table's add row (`draftRow`) starts from the `initialValues` its meta declares, as before, and so
+  // does a row that holds no object: for a `null` row, `data` is the document's (`mapper.tsx`), which placed there put a
+  // copy of the document inside the row.
+  const rowPlace = useForm && !draftRow ? rowPlaceOf(meta) : undefined
+  const place = rowPlace && isObject(initialValues) && initialValues !== (instance && instance.data) ? rowPlace : undefined
+  const formValues = useMemo(() => place ? setIn({}, place, initialValues) : initialValues, [place, initialValues])
+
   // TableCells only, or Data wrapping TableCells (e.g. renderExtraItem). Draft values stay in React state
   // until Add — no final-form fields at dataKind.*[nextIndex], so an empty `{}` is not materialized for the draft row.
   if (localDraft) {
@@ -117,7 +133,7 @@ export default function Data ({
     return <UIRenderWithUISetup
       data={data}
       meta={meta}
-      initialValues={initialValues}
+      initialValues={formValues}
       form={{kind}}
       parent={instance}
       index={rowIndex}

src/core/engine/__tests__/formData.select-order.test.js

@@ -4,8 +4,9 @@ import {
   getRawFormsData,
 } from '../formData'
 
-const makeForm = values => ({
+const makeForm = (values, fields = []) => ({
   getState: () => ({values}),
+  getRegisteredFields: () => fields,
 })
 
 const indexMeta = (mapOptions = {text: 'code', value: '{index}'}) => ({
@@ -190,7 +191,7 @@ describe('raw and structured forms data boundaries', () => {
       }],
       ['nested-row', {
         // Its fields are named by its row's place, `root.rows[1].value`.
-        form: makeForm({root: {rows: [undefined, {value: 'nested'}]}}),
+        form: makeForm({root: {rows: [undefined, {value: 'nested'}]}}, ['root.rows[1].value']),
         meta: {relativePath: 'root.rows', relativeIndex: 1},
       }],
     ])