Fix #498: Implement consistent logout experience across VS Code windows

[OyinloluB]

Problem

Issue #498 reported inconsistent behavior when users are logged out of Coder:

• Window A might show clear "please login" messages
• Window B would show confusing errors like "Invalid argument 'uriOrString'"
• Windows became unusable with no clear indication of what was wrong

Cause

Multiple VS Code windows share the same authentication storage, but when one window logs out, other windows aren't notified of the state change. This leads to:

• Inconsistent UI states across windows
• Confusing error messages instead of clear logout notifications
• Poor user experience

Solution

Implemented event-driven authentication synchronization using VS Code's ctx.secrets.onDidChange API:

1. Authentication Sync Function: syncAuth() updates REST client, VS Code contexts, and workspace providers when auth state changes
2. Event Listener: Detects session token changes across all windows
3. Consistent Notifications: All windows show clear "You've been logged out of Coder!" messages
4. UI State Sync: Sidebars and contexts update consistently across windows

Implementation

• Uses ctx.secrets.onDidChange for immediate, event-driven updates (no polling)
• Reuses existing logout notification patterns from Commands.logout()
• Updates restClient, VS Code contexts, and workspace providers consistently
• Proper cleanup via ctx.subscriptions for extension disposal

Testing

• A/B Validation: Confirmed bug exists without fix, disappears with fix
• Multi-window Testing: Tested logout sync across multiple Extension Development Host windows
• User Experience: Verified clear notifications replace confusing errors
• Debug Logs: Added logging to help reviewers verify fix during testing

Result

Eliminates confusing "Invalid argument" errors
Provides consistent logout experience across all windows
Clear user messaging with actionable "Login" button
Immediate synchronization (no delays)

Fixes #498

[OyinloluB]

Hi @aslilac

Connor asked me to tag you for review of this PR.

This fix addresses Issue #498 by implementing event-driven authentication synchronization across VS Code windows. When a user logs out from one window, all other windows now receive consistent "You've been logged out of Coder!" notifications instead of confusing error messages.

The solution uses ctx.secrets.onDidChange to detect session token changes and synchronizes the authentication state across all windows immediately.

I would be happy to address any feedback you have!

Thanks for taking the time to review!

[EhabY]

Closing this in favor of #590 since it handles both login and logout consistency and we need some urgency to land it.