Preserve custom query parameters in index search forms

[BriceFab]

Problem

When a CRUD index page is opened with custom query parameters (e.g. menu-driven list context such as _status, _discipline, or sort state), those parameters are correctly preserved in links generated by AdminUrlGenerator / ea_url(), but they are lost when submitting the index search form in real browsers.

This is because the search form uses method="get". Browsers only submit form fields, not the query string embedded in the form action URL.

Example

1. Open /admin/exercise?_status=to_complete
2. Search for squat
3. Browser navigates to /admin/exercise?query=squat — _status is gone

Functional tests using Symfony's KernelBrowser may pass without a workaround because the test client merges query parameters differently than real browsers.

Current workarounds

• Override search_form_filters in a custom crud/index template and add hidden fields for each custom parameter manually
• Migrate list context to official EasyAdmin Filters (filters[...]), which are already re-applied on search via hidden fields in layout.html.twig

Expected behavior

Custom query parameters that are not reserved EasyAdmin keys should survive search submissions, the same way:

• native filters[...] parameters already do (see [3.5.9] Searching does not respect active filters #4707)
• non-filter parameters are preserved in the filters modal form via form_action_query_string_as_array|ea_flatten_array in filters.html.twig

Related history

• How to pass new url parameter in entity in Easy Admin Bundle? #1573 — custom parameters preserved in links after Preserve the custom query parameters #2066, but search form still required manual hidden fields
• [3.5.9] Searching does not respect active filters #4707 — search did not respect active filters; fixed for native filters only

Proposed solution

Reuse the same hidden-field approach as the filters modal: preserve all remaining query parameters in the search form, excluding reserved keys (query, page, filters, batch params, etc.).

[BriceFab]

Proposed fix: #7639