[bhelm]

What this PR does

Changes heart-rate recovery eligibility on Swift and Android to require one continuous qualifying effort of at least two minutes. Previously, separate high-heart-rate fragments could be added together and incorrectly qualify a workout.

The calculation keeps the existing threshold, left-sample interval attribution, 10-second gap cap, duplicate-timestamp handling, recovery windows, and score outputs.

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Documentation
• CI / tooling

How it was tested

• Matching Swift and Kotlin regressions failed before the calculation change for disconnected runs, a gap over the cap, and a below-threshold reset.
• Focused Swift tests pass 12/12 using the actual analytics source, tests, and WhoopProtocol dependency in a minimal Linux package.
• Focused Android HeartRateRecoveryTest passes through testFullDebugUnitTest.
• Boundary coverage includes a gap exactly at the 10-second cap, a gap over the cap, exactly 120 continuous qualifying seconds, left-sample attribution, and duplicate timestamps.
• A focused differential check of 22 shared HRR cases produced byte-identical Swift/Kotlin output, including the corrected null result for disconnected effort. This used an isolated adapted fork harness, not the full fork governance/coverage guard: an unrelated obsolete runner dispatch was excluded with an explicit error, and the pre-fix known-bug oracle was retired without changing the input cases. A missing-result negative control failed as expected.

This is a pure analytics change and does not touch BLE behavior. No physical strap was tested. Local focused verification ran on Linux; the complete Swift package suite subsequently passed on macOS in Swift Packages CI, and the complete Android unit suite passed in Android CI.

Checklist

• Swift package tests pass for any package I touched (swift test in Packages/<name>) — complete StrandAnalytics package tests passed in macOS CI.
• Android unit tests pass if I touched android/ (./gradlew testFullDebugUnitTest) — complete unit suite passed in Android CI.
• No new build warnings introduced
• UI changes use only StrandDesign tokens — no UI changes
• No hardcoded hex frame bytes; protocol facts live in the schema / decoders — no protocol changes
• Follows the conventions in docs/CONTRIBUTING.md
• I did not commit generated output (Strand.xcodeproj/) or any secrets/keystores

Related issues

Fixes bhelm#55.