Add paging to the new pages parent picker

[nbradbury]

Description

The "Set Parent" picker in the new (wp-rs) pages list previously only offered pages that were already loaded into the tabs. On large sites this meant you couldn't choose a parent that hadn't been paged in yet, and its search field only filtered the loaded candidates.

Testing instructions

Requires a site with the experimental pages list enabled and enough published pages to paginate (more than ~20).

Parent picker paging:

1. Open the Pages list and tap a page's overflow menu → Set parent.
2. Scroll to the bottom of the candidate list.

• Verify more pages load automatically as you reach the end.

Server-side search:

1. In the Set parent sheet, type the title of a page that is NOT in the first loaded batch.

• Verify it appears in the results (previously it would not).

2. Clear the search field.

• Verify the "Top level" entry reappears and the full paged list returns.

Selecting a parent:

1. Pick a parent (or "Top level") and confirm.

• Verify the page's parent updates and the list refreshes.

[dangermattic]

	2 Warnings
⚠️	This PR is larger than 300 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.
⚠️	PR is not assigned to a milestone.

Generated by 🚫 Danger

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Android by scanning the QR code below to install the corresponding build.

	App Name	WordPress Android
	Build Type	Debug
	Version	pr23000-779d895
	Build Number	1497
	Application ID	org.wordpress.android.prealpha
	Commit	779d895
	Installation URL	53qfbh0gqdup8

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Android by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Android
	Build Type	Debug
	Version	pr23000-779d895
	Build Number	1497
	Application ID	com.jetpack.android.prealpha
	Commit	779d895
	Installation URL	2pk6se180si28

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[wpmobilebot]

🤖 Build Failure Analysis

This build has failures. Claude has analyzed them - check the build annotations for details.

[codecov]

Codecov Report

❌ Patch coverage is 8.28729% with 166 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.42%. Comparing base (2c13628) to head (779d895).

Files with missing lines	Patch %	Lines
...rdpress/android/ui/pagesrs/PagesRsListViewModel.kt	13.76%	87 Missing and 7 partials ⚠️
...roid/ui/pagesrs/screens/PageRsParentPickerSheet.kt	0.00%	64 Missing ⚠️
.../wordpress/android/ui/pagesrs/PageRsListUiState.kt	0.00%	6 Missing ⚠️
...ss/android/ui/pagesrs/screens/PagesRsListScreen.kt	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk   #23000      +/-   ##
==========================================
- Coverage   37.46%   37.42%   -0.04%     
==========================================
  Files        2325     2325              
  Lines      125245   125399     +154     
  Branches    17171    17205      +34     
==========================================
+ Hits        46918    46929      +11     
- Misses      74520    74656     +136     
- Partials     3807     3814       +7     

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[adalpari]

Claude pointed out a medium-severity issue:

1. Search race: overlapping init jobs are not cancelled (medium)
   onParentPickerQueryDebounced does closeParentPickerCollection() then initParentPickerCollection(), but closeParentPickerCollection() only closes the collection object — it does not cancel in-flight launchCollectionJob work (unlike clearCollections(), which cancels and recreates collectionsScope). On rapid query changes where two createParentPickerCollection IO calls overlap and complete out of order, parentPickerCollection = collection is a last-writer-wins assignment with no guarantee the survivor matches the latest query — the user can end up viewing stale search results. debounce(250ms) + distinctUntilChanged makes this unlikely but not impossible on slow networks.
   Consider giving the picker its own cancellable scope, or validating the assigned collection against the current query before publishing results.

[nbradbury]

Claude pointed out a medium-severity issue:

Thanks! Addressed in 174b931.

[adalpari]

Not a blocker, but the search results blink. I found a situation where it started to blink for like a second.

Screen_recording_20260618_142543.mp4

[adalpari]

Is this expected to happen?

2026-06-18 14:26:03.073  9555-9555  WordPress-PAGES         com.jetpack.android.prealpha         E  Failed to load more parents
                                                                                                    uniffi.wp_mobile.FetchException$StaleLoadMore: 
                                                                                                    	at uniffi.wp_mobile.FfiConverterTypeFetchError.read(wp_mobile.kt:11311)
                                                                                                    	at uniffi.wp_mobile.FfiConverterTypeFetchError.read(wp_mobile.kt:11300)
                                                                                                    	at uniffi.wp_mobile.FfiConverter$DefaultImpls.liftFromRustBuffer(wp_mobile.kt:270)
                                                                                                    	at uniffi.wp_mobile.FfiConverterRustBuffer$DefaultImpls.liftFromRustBuffer(wp_mobile.kt:286)
                                                                                                    	at uniffi.wp_mobile.FfiConverterTypeFetchError.liftFromRustBuffer(wp_mobile.kt:11300)
                                                                                                    	at uniffi.wp_mobile.FfiConverterTypeFetchError.liftFromRustBuffer(wp_mobile.kt:11300)
                                                                                                    	at uniffi.wp_mobile.FfiConverterRustBuffer$DefaultImpls.lift(wp_mobile.kt:287)
                                                                                                    	at uniffi.wp_mobile.FfiConverterTypeFetchError.lift(wp_mobile.kt:11300)
                                                                                                    	at uniffi.wp_mobile.FfiConverterTypeFetchError.lift(wp_mobile.kt:11300)
                                                                                                    	at uniffi.wp_mobile.FetchException$ErrorHandler.lift(wp_mobile.kt:11291)
                                                                                                    	at uniffi.wp_mobile.FetchException$ErrorHandler.lift(wp_mobile.kt:11290)
                                                                                                    	at uniffi.wp_mobile.Wp_mobileKt.uniffiCheckCallStatus(wp_mobile.kt:354)
                                                                                                    	at uniffi.wp_mobile.Wp_mobileKt.access$uniffiCheckCallStatus(wp_mobile.kt:1)
                                                                                                    	at uniffi.wp_mobile.Wp_mobileKt.uniffiRustCallAsync(wp_mobile.kt:13233)
                                                                                                    	at uniffi.wp_mobile.Wp_mobileKt$uniffiRustCallAsync$1.invokeSuspend(Unknown Source:19)
                                                                                                    	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
                                                                                                    	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
                                                                                                    	at kotlinx.coroutines.internal.LimitedDispatcher$Worker.run(LimitedDispatcher.kt:124)
                                                                                                    	at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:89)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:586)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:798)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:717)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:704)

[nbradbury]

Is this expected to happen?

Per Claude:

FetchException.StaleLoadMore is a benign race. So: yes, it’s expected to occur occasionally, 
but it shouldn’t have been treated as a user-facing error.

Fixed in 5a164bd

Not a blocker, but the search results blink.

I see what you mean. The bottom sheet resizes during search, first to show an empty list while the search results are being fetched, then again when search results are returned. I addressed this in 8ad34cc by making the sheet a fixed size.

[adalpari]

Thank you for the changes, LGTM!