The index.html boot guard now fires a fire-and-forget beacon (POST /telemetry/unsupported)
when it turns a client away on the unsupported-engine screen, so the owner can see — on the
Users dashboard beside "app opens" — how many real clients hit it and on which engines.
- Client: navigator.sendBeacon (fetch fallback) with a localStorage dedup keyed by app version
+ reason + Chromium, so a user reopening the app is one report, not ten.
- Gateway: a new unauthenticated POST /telemetry/unsupported handler (the client never booted,
so it carries no session), per-IP public-limited and body-capped, mirroring the export-download
route. It folds the beacon into the OTel counter unsupported_engine_total {reason =
no_bigint/no_proxy/boot_error/other, chromium}, with reason allow-listed and the Chromium major
reduced to a bounded range (normalizeUnsupported) so a spoofed beacon cannot inflate the metric
cardinality; the full user agent is logged, not labelled.
- Caddy: /telemetry/* added to the @gateway matcher (else it falls to the landing catch-all).
- Grafana: two panels on the Scrabble — Users dashboard (by reason, by Chromium major).
- Docs: ARCHITECTURE.md §11.
Tests: recordUnsupportedEngine (metric split), normalizeUnsupported (cardinality bounding), and
the handler route end to end (204 / 405 / counter). go build+vet+test and gofmt clean; ui
check/build/e2e green; the client beacon + dedup verified against a forced hard-gate (BigInt
removed) — one POST, deduped on reopen, correct reason/chromium/version labels.
Old Android System WebViews (the Telegram/VK in-app browser; a real device with Google
Play auto-updates the WebView, but emulators / no-Play / restricted devices stay frozen)
showed a white screen. Two causes, fixed in order:
- build.target es2022 shipped ?./?? verbatim, which the old engine cannot parse. Lowered
to es2019 so esbuild down-levels the syntax.
- The es2020+ runtime globals the bundle and its deps call (globalThis, structuredClone,
Array.at, ...) are missing on those engines. A conditional core-js loader (emitPolyfills
writes dist/polyfills.js, document.write'd by an index.html gate only when needed) covers
them; modern engines download nothing, so the bundle-size budget is untouched.
BigInt (the 64-bit FlatBuffers timestamp decode) and Proxy (Svelte 5 runes) cannot be
polyfilled, so the effective floor is Chrome 67. Below it, a permanent ES5 boot guard in
index.html shows a friendly "this device's OS or browser can't run the app" screen (with
the web-version link inside a Mini App) and a "Diagnostic information" view with a Copy
button, instead of a white screen. A reactive net raises the same screen on an uncaught
boot error that never signals window.__booted.
Board tile glyphs used container-query units (cqw, Chrome 105+) under .cell font-size:0,
so they collapsed to 0px on Chrome 74 (invisible letters); added vmin fallbacks.
The unsupported-engine telemetry beacon is a separate follow-up PR.
developer
Ilia Denisov