M0.2 — SW beacon-capture spike

Status: blocked in this environment. Requires launching real cross-browser instances (Chromium/Firefox/WebKit) with a live service worker and asserting whether the SW's fetch handler observes an outgoing fetch(keepalive)/sendBeacon call during page unload. This environment has no Playwright browser binaries installed and no ability to reliably simulate real unload timing across three engines in this pass.

What this blocks: deciding whether the service worker can be promoted from retry-only to a primary capture layer (Pre-mortem #1).

Default assumption taken in its absence (per plan Pre-mortem #1 and Requirements Summary): the SW's role defaults to retry-only — queued from the main thread on fetch/sendBeacon failure or offline detection, never assumed to reliably intercept unload-time beacons. This is the safe default and is what US-016 implements. Promotion to a capture role remains gated behind this spike passing, not assumed.

To unblock: install Playwright browser binaries (pnpm exec playwright install) and run the standing regression test referenced in the plan's Verification Steps once a target environment supports launching real browsers.

Update: Chromium browser binaries are now installed and launchable in this environment (see the Playwright browser e2e spike, updated in the same pass as this note). That spike's own AC14/AC16/AC27 e2e specs are a different question (SW registration/coexistence/kill-switch) and were not extended to cover beacon/fetch(keepalive) capture during unload — this spike's own "To unblock" steps (a dedicated beacon-capture regression test, ideally cross-browser) were not attempted here. Verdict below is unchanged.