---
tags:
  - work
  - cpm
  - tech-design
  - pixel
  - web-extension
updated: '2026-11-11'
status: draft
---
# TD: Pixel Definition: CPM Wake Init Detection (macOS/iOS + embedded web extension)

**Author:** Alex M
**Reviewer:** TBD
**Stakeholders:** Michal, Konrad, Russell
**Project:** [CPM: root-cause the stuck embedded extension messaging (macOS/iOS)](https://app.asana.com/1/137249556945/task/1216761517055116)

## Background & Requirements

The extension's background is unloaded when idle and woken when a page needs it. Failures after such a wake are the largest group of CPM failures with no fix: on macOS 1.214 they are 39% of all failures (0.68% of DAU), on iOS 7.244 22% (0.06% of DAU).

For one page, startup has these steps: the page script sends `init`; the background receives it; it reads the configuration; it reads the user setting from the app; it checks the site; it answers the page and sends the app a dashboard refresh. The app sees only the last step, so every failure looks the same: no answer.

We need to find where startup stops, without changing what the extension does for the page and without collecting URLs or persistent identifiers.

## Problem Statement

For every tab that the permanent breakage metric reports as silent, record the furthest startup step the extension reported.

## Recommended Approach

1. After each step the extension sends the app a short notification ([extension PR #3727](https://github.com/duckduckgo/duckduckgo-privacy-extension/pull/3727)). It does not wait for the app's reply.
2. For each tab the app remembers the furthest step reached.
3. When a tab is reported as silent, `web_extension_cpm_breakage` carries that step as a new parameter, `last_stage`:

| `last_stage` | What the app saw last |
|---|---|
| `none` | no notification (the background may not have run at all) |
| `page_init_sent` | the page script sent `init`, the background never processed it |
| `received` | the background got `init`, the configuration or storage read did not finish |
| `config_read` | the configuration was read, the user setting did not arrive |
| `settings_checked` | the user setting arrived, the site check did not finish |
| `site_checked` | all checks finished, no answer reached the app |
| `response_sent` | the background finished sending the answer to the page, no dashboard refresh followed |
| `response_failed` | sending the answer to the page failed |

4. These notifications and the parameter are temporary and are removed when the wake failures are fixed or the investigation is closed.

## Testing

Unit tests in the app and in the extension.

## Additional Considerations (if applicable)

1. Privacy
    1. New parameter `last_stage` on `web_extension_cpm_breakage`: one of eight fixed values.