🐛 fix(frames): exclude background time from frozen_frame / long_task, cap the duration, one span per stall

[nitinstp23]

Summary

Fixes B14-2083 (snabbit app-webview-rum: frozen_frame.duration up to 25 s, p90 ≈ 6 s on one screen). Also answers the client's question: the timer did not pause in the background.

• Web (long-task.ts). Long tasks are PerformanceObserver entries. Ordinary hidden-tab throttling does not fabricate them, but an Android WebView renderer suspended by its host mid-task reports one task covering the whole suspension when it resumes. The tracker now records hidden / freeze / resume intervals (the anr.ts pattern) and drops any entry overlapping one, ignores buffered entries that ended before install, and caps frozen_frame.duration at the new frozenFrameMaxMs (default 10 s, min 700 ms) with frozen_frame.capped: true. long_task.duration keeps the measured value.
• One stall, one span. Where PerformanceObserver.supportedEntryTypes includes long-animation-frame (Chrome 123+) the tracker no longer also observes longtask, which described the same stall twice (two long_task, two frozen_frame, two view.frozen_frame.count increments).
• React Native (frame-metrics.ts). The rAF-gap loop had no AppState guard, so the first frame after resume was a "frozen frame" as long as the background stay. It now follows AppState, resets its baseline across a background stay, and applies the same cap. AppState is injectable, so the loop finally has unit tests.

Tests

• long-task.test.ts (new): visible task → long_task + frozen_frame; task spanning a hidden interval dropped; task while hidden dropped; task before hidden kept; freeze/resume; pre-install buffered entry ignored; cap + flag; LoAF-only when supported, longtask fallback otherwise.
• frame-metrics.test.ts (new, first native test): frozen frame while active; background gap not reported and baseline reset; frames while backgrounded ignored; cap + flag; no AppState available.
• make ci green locally.

Docs

CHANGELOG [Unreleased], docs/configuration.md (frozenFrameMaxMs row, enableLongTaskDetection description), README frozen-frame row.

[nitinstp23]

Verification against scout-rum-example-apps/webview-react-web

Integration build = #9 + #10 + #11 merged locally (make ci green, 345 tests), packed and installed into the harness.

Headless Chrome 153 via Playwright, 29/29 (sessionSampleRate: 100, OTLP exports intercepted and parsed):

• Marker: written on load with sampled; visibilitychange:hidden clears it and the heartbeat keeps it cleared for 12.5 s; visible/freeze/resume re-arm; a seeded dead sampled session exports exactly one app_unclean_exit attributed to it (session.id = crash.previous_session_id), never app_crash; marker records reportedSessionId; an already-reported session and an unsampled session export nothing.
• Android WebView UA: no marker written, a pending marker is not filed, other spans still export.
• Array.prototype.at deleted before init: no TypeError, no error span, CLS/INP absent while TTFB/FCP/LCP report; an app error carries error.origin=app; an error whose top frame is the SDK module carries error.origin=sdk + sdk_internal, is exported once for three throws, and error.count stays at the one app error.
• 1 s stall → one long_task (LoAF only) + one frozen_frame (1.0 s); a stall overlapping a hidden interval is dropped; an 11 s stall reports 10 s with frozen_frame.capped=true.

Real Android System WebView (emulator API 34, Chrome 113, webview-bridge-flutter mode=off, DevTools over adb), 7/7: UA has wv; Scout.instance.config.enableUncleanExitDetection === false; no marker key in localStorage; 1 s stall → one long_task + one frozen_frame; HOME → visibilityState=hidden + app_paused; return → app_resumed; no app_unclean_exit/app_crash.

Kill cycle with the marker forced on (VITE_SCOUT_UNCLEAN_EXIT=true), 6/6: first launch reports nothing; HOME → 16 s → am force-stop → relaunch: no app_unclean_exit; foreground force-stop → relaunch: exactly one; a second foreground kill of the same (resumed) session: none; never app_crash.