DataTable nests `<form>` inside `<form>`

[cirdes]

• Where: DataTableForm wraps the table; DataTableSearch and
  DataTablePerPageSelect each render their own <form> inside it.
  Snapshot data_table/full_frame holds three <form elements.
• Effect: nested forms are invalid HTML. The parser ignores the nested
  search form's start tag — with its attributes and its
  data-controller="ruby-ui--data-table-search" — and its end tag closes the
  outer bulk form early, so the search controller never connects and the
  per-page form that follows ends up outside the bulk form. The controller's
  this.element.requestSubmit() therefore never runs at all. (The golden
  snapshot keeps all three forms because the suite parses inside a
  <template>, where the form-pointer rule does not apply.)
• Fix: render the search and per-page forms outside the bulk form, or
  make their controls reference it with the form= attribute; re-record (on the 2.0 line)
  data_table/*.
• 2.0 note: Herb's NestingValidator will likely reject this at compile
  time, so the DataTable migration ports the three forms as they are and then
  restructures them — a template adjustment with a reviewed snapshot change,
  on the 2.0 line, since main stays as is.

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Surfaced by the golden HTML suite (PR #536), which pins what 1.6 renders today — this defect included. Per maintainer decision (2026-09-19) main stays as is: this is addressed on the 2.0 line, and the golden snapshot that pins it is re-recorded there with the diff reviewed.

Source: design/v2/follow-up-issues.md.