Prevent notifications from crashing on malformed preference data

[Copilot]

Summary

Fixes #15281

Notification system crashes with TypeError: Cannot read properties of undefined (reading 'asCookie') when marking notifications as read/unread if the preference property is malformed (e.g., string instead of { key, value } object).

Occurred changes and/or fixed issues

Added defensive validation in shell/store/notifications.ts:

• isValidPreference() type guard validates preference structure before use
• markRead, markUnread, markAllRead actions now validate preferences and log errors instead of crashing
• Malformed preferences are skipped gracefully; valid preferences continue to work

Technical notes summary

The crash occurred because prefs/set expects { key, value } format. When preference is malformed:

1. key becomes undefined
2. definition lookup in prefs store fails (returns undefined)
3. Accessing definition.asCookie throws TypeError

Validation checks:

function isValidPreference(preference: any): preference is NotificationPreference {
  return preference !== null &&
    preference !== undefined &&
    typeof preference === 'object' &&
    !Array.isArray(preference) &&
    typeof preference.key === 'string' &&
    typeof preference.value === 'string' &&
    (preference.unsetValue === undefined || typeof preference.unsetValue === 'string');
}

Protects against: strings, arrays, nulls, objects with missing/wrong-type properties.

Areas or cases that should be tested

• Mark notification as read/unread with valid preference → works normally
• Mark notification as read/unread with malformed preference → no crash, error logged to console
• Mark all as read with mix of valid/invalid preferences → valid ones processed, invalid ones skipped
• Check console for descriptive error messages when invalid preferences encountered

Areas which could experience regressions

• Notification center read/unread toggle functionality
• Mark all notifications as read functionality
• User preference storage/retrieval for notifications
• Dynamic content notifications (announcements, release notes, support notices)

Screenshot/Video

Error before fix:

After fix: Application continues running, error logged to console for debugging.

Checklist

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• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes
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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Prevent Notifications to break if malformed or wrong data on "mark as read"</issue_title>
<issue_description># Description

In an accident related to a first use case of notifications, it appears that malformed or wrong data can break the application.
In this case it seems break if cookies are missing and data is not existing when flagging read the notifications.

Optionally: Create a type for notification data

</issue_description>

<agent_instructions>Ensure the fixes comment in the PR references issue 15281</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@richard-cox Just writing notes

• notification preference property was set to a string instead of { key, value } object
• pref store set action tried to find a preference (definition) with key undefined --> definition undefined --> definition.asCookie throws exception</comment_new>

• Fixes Prevent Notifications to break if malformed or wrong data on "mark as read" #15281

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