forms(qml): DynamicForm.gridColumns -- a host lays the fields out on a grid of its own

[Yaraslaut]

What / why

All of DynamicForm's field grids had fixed column counts:

• sections and tab sets used 2 columns
• the implicit flat bucket used 1
• the grid created inside a host's section/tab-set chrome was passed a literal 2

A host whose UI kit lays forms out on a 12-column grid could declare x-colspan, but the renderer never built a grid with that many columns to count the span against.

Contract

Property	Default	Applies to
gridColumns	2	Every section grid, every tab-set grid, and the grid createFieldGrid() creates inside a section/accordion/tab-set chrome.
flatGridColumns	gridColumns === 2 ? 1 : gridColumns	The implicit flat bucket: the whole form when there is no x-layout, plus the trailing group of fields no group names. It is 1 at the default, which is the pre-grouping renderer's single column. When a host sets gridColumns, this follows it, so gridColumns: 12 alone is enough. A host can also set it directly.
x-colspan	1	Clamped to the column count of the grid it sits in. A span wider than the grid takes one full row instead of widening the grid.

Both properties are bindings, so changing one re-lays the form. createFieldGrid(chromeItem, fieldsOf) no longer takes a columns argument; the grid binds gridColumns itself.

Default = unchanged layout. With both properties left alone, every grid keeps its old column count and every pre-existing forms test passes as before. One behavior is new at the default: x-colspan is now clamped to the grid's column count. Previously, an x-colspan of 2 on a field in the 1-column flat bucket was passed through unclamped.

Tests

The new src/qt/forms/tests/tst_DynamicFormGridColumns.qml has 9 cases. It covers:

• the defaults
• gridColumns: 12 on flat, section, tab-set and chrome-hosted grids, including where the fields actually land (two 6-span fields share a row)
• the clamp
• setting flatGridColumns on its own
• re-layout when the property changes

Mutation checks (actually run):

Break	Red
Every grid set back to a fixed 2/1 columns	5 of 9
Span clamp removed	5 of 9

Local run on MSVC / Qt 6.11.1 with QT_QPA_PLATFORM=offscreen: forms_qml_logic 405 passed, 0 failed.

Independent of #822; the two touch different parts of DynamicForm.qml.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!