Why

This PR modernizes administrator UX in com_content with progressive async behavior while preserving full synchronous fallback and existing server-side ACL/CSRF protections.

Scope delivered

1. Async admin contract foundations

• Feature-flag plumbing for async backend behavior in com_content.
• Reusable normalized async JSON envelope trait.
• Shared client async helper with graceful fallback.

2. Async list interactions in Articles manager

• Async state actions (publish, unpublish, archive, trash, featured, unfeatured).
• Async workflow transitions.
• Async search/filter/order/pagination with list fragment refresh.

3. Autosave in Article edit

• Autosave scheduler + dirty-state tracking.
• Async autosave endpoint contract + status payload.
• Versioning-safe policy:
  • skip unchanged payload
  • throttle by configured autosave interval
• Recover last autosaved snapshot + undo recover (session-local MVP).

4. Custom-field filtering in Articles list

• Custom-field filter controls in search tools.
• Query integration for selected custom field + optional value match.

5. Shared hooks + accessibility

• Reusable async fragment refresh hooks.
• Focus restoration after async refresh.
• aria-live async announcement handling.

Addressed review findings in this update

• Replaced Object.hasOwn(...) with Object.prototype.hasOwnProperty.call(...).
• Added redirect handling control (followRedirect) so list flows can refresh fragments without forced navigation.
• Added isAsyncEnabled() guards in Joomla.submitbutton and Joomla.listItemTask overrides so flags-OFF behavior remains classic/synchronous.
• Fixed async fallback path to preserve task handling via original submit path.
• Autosave guard state is now persisted only on successful autosave.
• Custom-field controls are removed when no custom fields are available.
• Custom-field query uses EXISTS subquery to avoid duplicate article rows.
• Cypress autosave initialization test now calls Joomla.contentAutosave.setup() after runtime options are loaded.
• Fixed PHPDoc alignment in async response trait.

AI disclosure (Joomla policy)

This PR is AI-assisted and explicitly labeled per policy.

I confirm:

• I manually reviewed and understood all changed code.
• I validated behavior and adjusted generated code where needed.
• I checked fallback/safety behavior (flags OFF and ON paths).
• I removed/rewrote issues identified in prior review.
• I am fully responsible for correctness, security, maintainability, and licensing compatibility.

Validation performed

• Unit tests:
  • tests/Unit/Libraries/Cms/MVC/Controller/AsyncAdminResponseTraitTest.php (2 passed)
• Manual verification checklist:
  • Flags OFF: classic full submit behavior in list/edit
  • Flags ON: async list actions/transitions/filters/pagination
  • Autosave statuses: pending/saving/saved
  • Autosave skip policy: unchanged/throttled
  • Recover + undo recover
  • Custom field filter visibility and filtering
  • Accessibility: focus restoration + aria-live messages

Risk / rollout

• Scope is intentionally limited to com_content as pilot.
• Async behavior remains feature-flag gated.
• Non-async paths remain available and functional.
• Server-side ACL/CSRF checks are unchanged.