fix(plugin-form): the line-items panel neither draws nor saves the lines it holds for another parent record (objectui#10740)

.changeset/10740-line-items-held-for-another-parent.md

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+---
+'@object-ui/plugin-form': patch
+---
+
+fix(plugin-form): the line-items panel neither draws nor saves the lines it holds for another parent record (objectui#10740)
+
+The `record:line_items` panel (`LineItemsPanel`) holds one set of rows, replaced
+when a load commits. When the host moved the panel to another parent record
+without a remount and that parent's load failed, the previous parent's lines
+stayed on screen, edits included, drawn editable with Save enabled; Save then
+wrote them under the new parent's id, moving another record's lines to it. A load
+that declined for the new parent (a refused filter) drew the decline's own notice
+but left the same Save enabled over the same held rows.
+
+Now the panel records which parent its held rows belong to, wherever the rows are
+written: a load's commit, or an edit made before any load settled. While that
+parent is not the current one, no held line is drawn (after a failed load a
+placeholder stands where the grid would be, under the failure's banner; after a
+refused-filter decline that filter's own notice stands there, as before; after a
+lost-adapter decline the placeholder stands alone), the Save button is off, and a
+save sends nothing. A load for the current parent that commits
+takes the grid back. Unchanged: a load for the new parent that succeeds replaces
+the rows as before, and a re-load of the same parent that fails keeps the
+author's unsaved edits drawn, editable and saveable under that parent.