refactor(Android, Stack v5): separate React and native domains in header implementation

[kligarski]

Description

Closes https://github.com/software-mansion/react-native-screens-labs/issues/1519.

Changes

WIP

Before & after - visual documentation

WIP

Test plan

WIP

Checklist

• Included code example that can be used to test this change.
• For visual changes, included screenshots / GIFs / recordings documenting the change.
• For API changes, updated relevant public types.
• Ensured that CI passes

[Copilot]

Pull request overview

Refactors the Android (Stack v5 / “gamma”) header implementation to better separate the “React config” domain (state/props/events) from the “native header view” domain (toolbar/appbar construction and updates), while also improving teardown to avoid leaking Fabric UIManager listeners.

Changes:

• Replaces the monolithic StackHeaderCoordinator with a slimmer StackHeaderCoordinatorLayout + new StackHeaderApplicator, and introduces an observer/flags-based update pipeline (StackHeaderConfigurationObserver, StackHeaderUpdateFlags).
• Reworks header config attachment to pass both a configuration provider and a native delegate (OnHeaderConfigurationAttachListener, StackHeaderDelegate) and moves layout-to-shadow-state syncing through the delegate.
• Adds explicit teardown paths for Fabric UIManager listeners in StackHost and StackHeaderConfig via onDropViewInstance.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
android/src/main/java/com/swmansion/rnscreens/gamma/stack/screen/StackScreen.kt	Renames/reshapes header-config attach listener API; refactors shadow-state syncing entrypoints.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/host/StackHostViewManager.kt	Calls tearDown() on host drop to unregister UIManager listeners.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/host/StackHost.kt	Uses getFabricUIManagerNotNull and adds tearDown() to remove UIManager listener.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/toolbar/StackHeaderToolbarMenuCoordinator.kt	Deleted; toolbar menu logic moved into applicator.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/subview/StackHeaderSubviewProviding.kt	Removes origin-offset update API from the provider interface.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/subview/StackHeaderSubview.kt	Adjusts subview change listener naming and keeps origin shadow-state updates local to the subview.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/subview/OnStackHeaderSubviewChangeListener.kt	Renames callback method to onStackHeaderSubviewChanged().
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/StackHeaderCoordinatorLayout.kt	Implements new attach/observe/update flow; delegates shadow-state updates; rebuilds header via applicator.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/StackHeaderCoordinator.kt	Deleted; responsibilities split into coordinator layout + applicator.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/StackHeaderApplicator.kt	New; owns header view construction and incremental application of config changes.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/StackHeaderAppBarLayout.kt	Adds managed title support storage to support applicator-managed title view.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/config/StackHeaderUpdateFlags.kt	New; introduces bitflags describing which parts of header need updating/rebuild.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/config/StackHeaderDelegate.kt	New; defines the native delegate contract for frame/subview/menu click callbacks.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/config/StackHeaderConfigViewManager.kt	Stops calling legacy change notifier; adds tearDown() on drop.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/config/StackHeaderConfigurationProviding.kt	Renames config provider interface and replaces delegates with a single observer setter.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/config/StackHeaderConfigurationObserver.kt	Renames/reshapes observer interface to include update flags.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/config/StackHeaderConfig.kt	Implements provider + delegate; adds flags-based invalidation and flush on Fabric mount completion; adds UIManager listener teardown.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/config/OnHeaderConfigurationAttachListener.kt	New; attach callback that passes provider + delegate separately.
android/src/main/java/com/swmansion/rnscreens/gamma/stack/header/config/OnHeaderConfigAttachListener.kt	Deleted; replaced by the new attach listener contract.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.