[6.x] Reduce publish container value cloning and emission overhead

[jasonvarga]

Extracted from #15158

The publish container's visibleValues computed cloned the entire values tree — JSON.parse(JSON.stringify(...)) via Values — on every keystroke, and a separate deep watcher then re-traversed that derived tree in order to emit it. Neither is necessary in the common case.

Two independent changes, in separate commits:

Skip the clone when nothing is omitted. Field conditions only omit values when a field is hidden with omitValue. When nothing is omittable — the common case — visibleValues now returns the live tree instead of a copy. The cloning path is unchanged when there is actually something to strip out.

Emit without deep watching the derived tree.visibleValues is derived from values and hiddenFields, so it's now emitted alongside update:modelValue from the existing values watcher, and the separate deep watcher watches the much smaller hiddenFields object rather than re-traversing the whole values tree.

Emission behaviour is unchanged. I traced the emission sequence on 6.x and on this branch with the same instrumented test, and the count, order and payloads are identical for value edits, nested edits, wholesale replacement via setValues, and conditions toggling a field on or off.

Nothing here touches which fields get omitted.

One note for addon authors: on the non-omitting path visibleValues is now the live values tree rather than a copy, so it must be treated as read-only. Nothing in core mutates it, and nothing in core listens to update:visibleValues.

Adds resources/js/tests/components/ui/Publish/VisibleValues.test.js, covering the uncloned tree's equivalence to a clone (including identical serialization) and the emissions for each of the cases above.

[jasonvarga]

Closing this one — it's a breaking change.

visibleValues is documented addon API. Returning the live values tree instead of a copy changes more than just "treat it as read-only":

• mutations now leak into form state
• visibleValues === values becomes true, so the two trees can't be told apart
• structuredClone on it throws, which breaks worker/IndexedDB paths
• a non-deep watch(visibleValues, cb) silently stops firing
• retained references alias, so held snapshots rewrite themselves

The old clone was also normalizing via a JSON round trip, so Dates and undefined values now survive where they previously didn't.

Too much to put on a released line.