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+---
+title: 'CPM — metrics, causes and mitigations'
+date: '2026-10-16'
+tags:
+  - work
+  - cpm
+  - analysis
+---
+# CPM: metrics, causes and mitigations
+
+Updated 16 October 2026. Internal metrics; keep these figures out of public PRs. `cpm-e2e-init` is the local test/fix worktree referenced here.
+
+## What the metrics mean
+
+The monitor reports failure when no matching native dashboard refresh arrives within 4 seconds of navigation completion. A second qualifying timeout marks the episode stuck and triggers M4 extension reload. Neither timeout nor recovery proves delivery of `initResp` to the page: tests can receive it while dashboard delivery fails.
+
+Daily pixels count installation-days per event/reason, not distinct users or episodes. Independently deduplicated failure/recovery totals cannot establish transition or recovery success rates. Keep `.count` separate from `.daily`.
+
+## Distribution
+
+Latest received production cut: **12–14 October**, iOS 7.240+ / macOS 1.210+. Figures below always use **iOS / macOS** order.
+
+- Initial failures: **3,273,025 / 119,950**; stuck: **511,660 / 40,842**.
+- Recovery without reload: **1,135,477 / 30,738** (34.7% / 25.6% of initial-failure daily totals).
+- Recovery after M4: **293,557 / 21,865** (57.4% / 53.5% of stuck daily totals); reload-failed reports: **140,921 / 17,796** (27.5% / 43.6%). These are ratios of event totals, not episode outcomes.
+
+Mutually exclusive snapshot cohorts, in classification priority order. Each pair shows **share of initial failures → share of stuck**:
+
+- Error 6: **6.1% → 21.5% / 1.0% → 1.9%**.
+- No background view: **48.1% → 10.9% / 3.3% → 1.8%**.
+- Tab detached: **0.03% → 0.05% / 6.2% → 8.9%**.
+- Network process replaced: **16.8% → 39.7% / 13.6% → 26.6%**.
+- Recent wake: **7.9% → 9.5% / 32.5% → 32.2%**.
+- Recent context load: **15.7% → 6.0% / 20.0% → 6.4%**.
+- Other: **5.3% → 12.5% / 23.4% → 22.2%**.
+
+These classify observed state, not causes. Network replacement and error 6 are more prominent in stuck; missing-view and recent-load cases are less prominent.
+
+Earlier **5 October post-release** cut: initial failures **6,624 / 1,377**, stuck **1,440 / 487**, first post-reload timeouts **670 / 232**. It established the same wake/load distinction; its different window and filters must not be combined with the newer totals. [[cpm-web-extension-public-attribution-2026-10-05|Original cut]] · [[cpm-web-extension-data-analysis-summary-2026-10-08|Earlier analysis]]
+
+## Causes and suggested mitigations
+
+- **Network crash:** reproduced across tabs/windows; a surviving background view can retain a dead worker after Network-process replacement. Fix B restarts the background. Production attribution remains incomplete: `network_restarted` compares against context load, not the latest view. Add `network_replaced_since_view`; the older analysis supports at most 20–45% of healthy-looking stuck reports, not the whole cohort.
+- **P1, slow idle wake:** an imposed startup delay reproduces timeout followed by a late answer; natural production slowness remains unexplained. Local mitigation prepares background before navigation, with a shared, cancellable **5-second maximum wait**. It passed with an 8-second worker delay; longer delays remain possible.
+- **P2, error 6:** controlled macOS suspension reproduces WebKit's roughly 30-second background-load timeout. The main iOS chains remain unproven. Local mitigation retries `loadBackgroundContent` once on the current context, with cooldown and recovery guards. Same-document dashboard **and page initResp** recovery passed twice. Full-context replacement was rejected after repeat page-response loss. Foreground-resume recovery remains untested.
+- **P3, loaded context without view:** startup dominates on iOS. Base-URL cleanup can delay startup, but the full P3 failure remains unreproduced, including the 20,000-resource cache test. Stable extension base URL is an unfinished candidate.
+- **P4, first mid-session load:** early init loss is reproduced; Fix A waits for first background readiness. Its signature covers only **3.9% of iOS initial failures and 0.9% of stuck** (129k → 4.6k), and can include reloads.
+- **P5, tab registration lost:** closing a window containing a shared pinned tab makes WebKit unregister the surviving tab. Correct window/tab lifecycle reporting is the mitigation to develop. The mechanism covers macOS `tab_in_context=false`; other P5 cases remain unexplained. Separate 14 October selection: **68 of 499** macOS P5 reports have that flag; the earlier 494-report selection used different filters.
+- **P6, controller mismatch:** a main `webExtensions` flag cycle creates a new manager while existing web views retain the old controller. Recreate/rebind affected views when replacing the manager; context reload alone cannot repair this. The conditional mechanism is reproduced, but its occurrence in production is unconfirmed. Selected macOS tails: **627 + 235** reports.
+- **Other:** no established cause. Readiness timing, init progress and healthy-load baselines are needed before selecting a mitigation.
+
+## Open PRs and local validation
+
+**Last verified open: 15 October, 17:26 UTC. Live GitHub access was declined in this pass; current state is unverified.**
+
+- [#7376](https://github.com/duckduckgo/apple-browsers/pull/7376): readiness/recovery telemetry; [#7384](https://github.com/duckduckgo/apple-browsers/pull/7384): healthy readiness baselines; [#7385](https://github.com/duckduckgo/apple-browsers/pull/7385) + [extension #3727](https://github.com/duckduckgo/duckduckgo-privacy-extension/pull/3727): native/JS init progress.
+- [#7378](https://github.com/duckduckgo/apple-browsers/pull/7378): repro harness → [#7379](https://github.com/duckduckgo/apple-browsers/pull/7379): Fix A → [#7381](https://github.com/duckduckgo/apple-browsers/pull/7381): Fix B. Last check: #7384/#7385 failed Danger; #7381 failed Non-Sandbox. B's corrective commit was local only.
+- The newer [PR0 episode-report proposal](cpm-pr0-episode-telemetry-summary-2026-10-16.md) replaces separate failure/recovery events with one terminal episode report; it supersedes the older reporting design, not the historical measurements.
+
+**Local `cpm-e2e-init`, 16 October:** P1/P2 candidates remain uncommitted. **22 unique app methods passed across separate runs**; two deliberate disabled-fix controls failed. Package validation: **806 tests, 14 skipped, zero failures**. Tests use real app/WebKit paths with an instrumented bundle and imposed faults; they do not identify every production cause. P3 remains unreproduced; app P5 establishes one lost navigation. No shipped-effect claim.
+
+Detailed evidence and final validation: [[cpm-status-2026-10-15]] · [[cpm-web-extension-code-guide-2026-10-09]].