## Context

Split off from #OP-19618 (Part B), which originally bundled this with CSP nonce enforcement (now its own consolidation, OP-19618, stacked on PR #23980 / #24033). Splitting because this half has an open design question the other did not, and is independent scope.

## Three mechanisms protect custom elements from morph; make it one policy

Three places independently decide what happens to a custom element when idiomorph runs, each with a different rule:

Begin of the insertion* End of the insertion Begin of the deletion -End of the deletion `frontend/src/turbo/turbo-global-listeners.ts` — `turbo:before-morph-element` blanket `preventDefault()` on any `OPCE-*` element. Begin of the insertion

* End of the insertion Begin of the deletion
-End of the deletion `frontend/src/turbo/action-menu-morph-remount.ts` — `turbo:morph-element` clones the `<action-menu>` host to force `connectedCallback` to re-fire. Begin of the insertion

* End of the insertion Begin of the deletion
-End of the deletion `frontend/src/stimulus/controllers/dynamic/work-packages/dialog/preview.controller.ts` — its own `beforeNodeMorphed` that skips `OPCE-*` unless a scheduling flag flips. Begin of the insertion


End of the insertion Begin of the deletion

End of the deletion The root fact Begin of the insertion(&quot;Primer/AngularEnd of the insertion Begin of the deletion ("Primer/AngularEnd of the deletion custom elements do not survive morph Begin of the insertioncleanly&quot;)End of the insertion Begin of the deletion cleanly")End of the deletion is re-discovered and re-encoded three ways; a fourth bug will likely become a fourth special case.

Begin of the insertion* End of the insertion Begin of the deletion -End of the deletion Extract a single custom-element morph policy with a small interface (e.g. `shouldMorph(node)` / `onMorphSkipped(node)`) consumed by all three call sites. Begin of the insertion

* End of the insertion Begin of the deletion
-End of the deletion Confirm during design whether one policy covers all three cases (whole-page vs frame vs single host) or only two — they are subtly different. Begin of the insertion


End of the insertion Begin of the deletion

End of the deletion ## Notes

Relates to #DREAM-514 and #OP-19618 (the CSP nonce consolidation, sibling work). The `turbo_power` allowlist in `setup.ts` is being addressed upstream via Begin of the insertionhttps://github.com/marcoroth/turbo\_power/pull/333End of the insertion Begin of the deletion https://github.com/marcoroth/turbo_power/pull/333End of the deletion and is intentionally out of scope here. Begin of the insertion

### Hints for QA

Changes are DX-focused. Does not need manual QA.End of the insertion