### Testing Steps

Run each case with fresh app data so daily pixel deduplication does not hide results. In Xcode’s console, filter by `PixelKit` Category.

#### Healthy navigation

1. Open a web page.
2. Wait at least 5 seconds → no `debug_web_extension_cpm_*` pixel is sent.
3. Open **Debug → Web Extensions → Simulate CPM Messaging Breakage (On)**.
4. Open New Tab, Settings, Bookmarks (internal pages), validate no `debug_web_extension_cpm_*` pixel is sent

#### Failure, stuck, and recovery

1. Open **Debug → Web Extensions → Simulate CPM Messaging Breakage (On)**.
2. Load a web page and wait 5 seconds → `debug_web_extension_cpm_initialization_failed_after_other` is sent; no `stuck` pixel is sent.
3. Navigate to another HTTP(S) page and wait 5 seconds → `debug_web_extension_cpm_messaging_stuck_other` is sent.
4. Select **Simulate CPM Messaging Breakage (Off)**.
5. Reload the page → `debug_web_extension_cpm_messaging_recovered_without_extension_reload` is sent.
6. Navigate again → no additional CPM failure or recovery pixel is sent.

#### Session restoration
1. Open a web page 
2. Dupli

#### Concurrent navigations

1. Select **Simulate CPM Messaging Breakage (On)**.
2. Load HTTP(S) pages in two tabs before either 4-second timeout expires.
3. Wait 5 seconds → initialization failures are observed, but no `debug_web_extension_cpm_messaging_stuck_*` pixel is sent.
4. Start another navigation after those failures and wait 5 seconds → `debug_web_extension_cpm_messaging_stuck_other` is sent.

#### Extension reload

1. Start with **Simulate CPM Messaging Breakage (Off)** and use the Fire button to trigger extension reloading.
2. After data clearing completes, select **Simulate CPM Messaging Breakage (On)**.
3. Load a web page and wait 5 seconds → these pixels are sent:
    - `debug_web_extension_cpm_initialization_failed_after_extension_reload`
    - `debug_web_extension_cpm_messaging_extension_reload_failed`
4. Navigate again and wait 5 seconds → `debug_web_extension_cpm_messaging_stuck_extension_reload` is sent.
5. Select **Simulate CPM Messaging Breakage (Off)** and reload → `debug_web_extension_cpm_messaging_recovered_after_extension_reload` is sent.