Prevent signing in with another WP.com account

[crazytonyli]

This is the alternative solution to #23654.

Eventually, we'd want to add multi-account support, we'll disable signing in with another WP.com account for now.

However, it's also important that we don't make the assumption that there is only one WPAccount. Always looking up accounts based on context (username, email, account associated with a given site, etc) will make our life easier when adding multi-account support to the app.

Before	After

Regression Notes

1. Potential unintended areas of impact

2. What I did to test those areas of impact (or what existing automated tests I relied on)

3. What automated tests I added (or what prevented me from doing so)

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Testing checklist:

• WordPress.com sites and self-hosted Jetpack sites.
• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• VoiceOver.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• iPhone and iPad.
• Multi-tasking: Split view and Slide over. (iPad)

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 25.5. 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

[wpmobilebot]

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

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr23682-8ceb405
	Version	25.4.1
	Bundle ID	org.wordpress.alpha
	Commit	8ceb405
	App Center Build	WPiOS - One-Offs #10887

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

[wpmobilebot]

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

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr23682-8ceb405
	Version	25.4.1
	Bundle ID	com.jetpack.alpha
	Commit	8ceb405
	App Center Build	jetpack-installable-builds #9928

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

[kean]

It works as described.

It's not great, but at least it's now (more) clear what's going on.