Fix GutenbergKit editor issues during dark mode toggle

[oguzkocer]

Summary

Fixes content loss and WebView loading issues when toggling dark mode while using the GutenbergKit editor.

Problem

• Content loss: Editor content disappeared when toggling dark mode
• WebView loading issues: Blank WebView after dark mode toggle on private sites
• Root cause: Double editor initialization due to duplicate auth state handling and isEditorStarted flag preventing proper reinitialization

Solution

• Prevent duplicate fetchWpComCookies() calls by checking existing auth state
• Add ViewPager duplicate setup protection with error logging
• Use distinctUntilChanged() to prevent duplicate LiveData emissions
• Remove isEditorStarted flag that was preventing proper editor reinitialization
• Consolidate auth success handling logic

Demo

dark_mode_toggle_fixed.webm

Testing Instructions

Prerequisites

• Test with both private WordPress.com sites and simple sites
• Ensure GutenbergKit editor is enabled

Test Cases

1. Dark Mode Toggle Test

   • Open a post in GutenbergKit editor
   • Add some content to the editor
   • Toggle device dark mode
   • Verify: Content is preserved and editor loads correctly
   • Toggle device dark mode again
   • Verify: Content is preserved and editor loads correctly

2. Device Rotation Test (Regression Test)

   • Open a post in GutenbergKit editor
   • Add some content to the editor
   • Rotate device (portrait ↔ landscape)
   • Verify: Content is preserved and editor loads correctly (ensure no regressions)

Expected Results

• ✅ Editor content is preserved during dark mode toggle
• ✅ WebView loads correctly (no blank screen)
• ✅ No duplicate editor initialization warnings in logs
• ✅ Smooth transitions without content loss

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 26.1. The due date for this milestone has already passed. Please assign it to a milestone with a later deadline or check whether the release for this milestone has already been finished.

Generated by 🚫 Danger

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[wpmobilebot]

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

	App Name	WordPress
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr22135-c010176
	Commit	c010176
	Direct Download	wordpress-prototype-build-pr22135-c010176.apk

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[wpmobilebot]

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

	App Name	Jetpack
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr22135-c010176
	Commit	c010176
	Direct Download	jetpack-prototype-build-pr22135-c010176.apk

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 39.74%. Comparing base (205b7da) to head (c010176).
⚠️ Report is 1 commits behind head on release/26.1.

Additional details and impacted files

@@               Coverage Diff                @@
##           release/26.1   #22135      +/-   ##
================================================
+ Coverage         39.43%   39.74%   +0.30%     
================================================
  Files              2149     1572     -577     
  Lines            101872    73737   -28135     
  Branches          15604    11925    -3679     
================================================
- Hits              40177    29306   -10871     
+ Misses            58126    41912   -16214     
+ Partials           3569     2519    -1050     

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[dcalhoun]

Thank you for helping to identify and land this fix. 🙇🏻‍♂️

I tested Simple and Atomic sites, private and public sites, appearance changes, orientation changes, and smoke tested editor functionality. The changes function well overall.

I did note an apparent race condition or memory leak may remain. I am able to discard the editor content after several OS appearance toggles.

Discard editor contents w/ multiple appearance toggles

Screen_Recording_20250815_074141_Jetpack.mp4

However, this appears present in 26.0 as well. Given that, I believe we should move forward with this fix; it's a definite improvement for the release branch. We can then spend time later seeking to address the core issue.

In the future, I envision us addressing two separate things:

• Optimize editor create/destroy logic to mitigate race conditions and memory leaks
• Manage uiMode configuration changes similar to how we handle other configuration changes (e.g., device orientation change)

The second will be easier once GBK has its own separate activity, where we can make changes without impacting the other editors.