Dehydrate an action modal's form data on submit

[ONyklicek]

The write path has had a named seam since ADR 0021 — a field shapes its own value on the way out — but it had exactly two hosts: Form::save() through SaveHandler, and an editable table cell through updateTableCell(). An action modal was not one of them. submitActionModal() / callMountedAction() read mountedActions.{depth}.data and handed it to the callback untouched, so the same schema wrote different values depending on which host persisted it: Select::dehydrateState()'s documented '' -> null rule simply did not apply inside a modal, and a cleared numeric field reached the column as '' — SQLSTATE[22007] "Incorrect decimal value: ''" on any strict MySQL.

The schema walk moves out of SaveHandler into Forms\Runtime\StateDehydrator, the canonical owner both hosts now call, and the action runtime gains the seam next to the validation one it already had: dehydrateMountedActionFormData(), a no-op in core, overridden by the wire-forms bridge, so a form-free host is unaffected. Wizards dehydrate every step, not only the one on screen at submit; repeater children are dehydrated per item. Footer actions are deliberately excluded — they read the form mid-edit and write back into the same bag, so dehydrating there would hand the callback a value the form no longer holds, and would run a FileUpload's store on a form the user never submitted.

TextInput had no dehydration at all, so numeric() was a rendering hint and nothing more — this half reached Form::save() too. A field whose HTML type is number now stores null when it is left empty; every other type is untouched on purpose, because '' is a legitimate string and nulling it would break a non-nullable text column rather than save it.

The tests are mutation-checked: removing either call site fails them.

[chatgpt-codex-connector]

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