Fix: scope Health Connect aggregate null-bucket skip to HEART_RATE only

[dmarttila]

Summary

PR #18 ("Stream Health Connect reads page-by-page + optional native downsampling (fixes HR OOM)") changed getAggregateHCData in HealthPlugin.kt so that a missing/empty aggregate bucket is skipped entirely (?: continue) instead of falling back to 0. The stated rationale was heart-rate specific: a 0 BPM reading is not a real data point, so it shouldn't be fabricated for buckets with no HR samples.

That rationale is correct for HEART_RATE, but the continue was applied unconditionally to every metric type this function handles via MapToHCAggregateMetric — STEPS, WEIGHT, HEIGHT, DISTANCE_DELTA, WATER, the SLEEP_* duration types, ACTIVE_ENERGY_BURNED, and TOTAL_CALORIES_BURNED. For all of those, zero is a legitimate, meaningful value for a bucket (e.g. 0 steps taken, 0 meters traveled, 0 calories burned in an interval with no activity). Skipping the bucket instead of reporting 0 silently drops real data for every non-HR caller.

This PR scopes the skip-on-null behavior to dataType == HEART_RATE only, and restores the old zero-fallback for every other aggregate metric type.

• What Stream Health Connect reads page-by-page + optional native downsampling (fixes HR OOM) #18 changed: empty/missing aggregate buckets are skipped (?: continue) rather than fabricating 0.
• Why that's right for heart rate, wrong for everything else: a missing HR bucket means "no samples," and 0 BPM isn't a real physiological reading — but a missing steps/distance/calories/etc. bucket legitimately means "0 occurred in this interval," which is real, reportable data.
• What this PR does: scopes the skip to HEART_RATE only; every other metric type gets the old zero-fallback back.

No current caller in shiftapp_flutter is affected — it only queries HEART_RATE aggregates — but this is a shared plugin fork, and any other/future caller of a non-HR aggregate type would otherwise get silently-missing buckets instead of zeros.

This was caught in review after #18 merged — it's a latent scope issue present in the original PR, not a regression introduced by this change.

Related: #18

Out of scope (noted, not touched)

Two issues were identified in the surrounding code during this review but are explicitly out of scope for this PR and were not touched:

• A pre-existing bug (predating Stream Health Connect reads page-by-page + optional native downsampling (fixes HR OOM) #18) where the SleepSessionRecord branch in getHCData reads response.records from only the last page of a paginated sleep query instead of accumulating across all pages.
• An unverified assumption that Health Connect records arrive in non-decreasing chronological order across pages, which the samplingIntervalMillis downsampling in getHCData relies on — not confirmed as a bug, needs real-device validation.

Diff

Single-file, Kotlin-only change in packages/health/android/src/main/kotlin/cachet/plugins/health/HealthPlugin.kt, scoped entirely to the null-bucket-handling block inside getAggregateHCData. Does not touch getHCData, the page-by-page/samplingIntervalMillis downsampling logic, the HEART_RATE to HeartRateRecord.BPM_AVG mapping, or the try/catch around getAggregateHCData — all added by #18 and correct/unrelated.

Test plan

• Manual review of the diff and surrounding Kotlin control flow (null-check branching, smart-cast to non-null before is Length / is Energy checks and the mapOf construction).
• Could not run a full Gradle/Kotlin compile in this sandbox — packages/health/example/android fails to build with flutter build apk --debug due to a pre-existing, unrelated Flutter-Gradle-plugin-loading incompatibility (the example project uses the legacy imperative apply style, which the installed Flutter 3.35.4 toolchain rejects). This is a project-config issue independent of this change and was not touched.
• There is no Kotlin unit test suite in this package (android/src/test doesn't exist), consistent with the rest of the codebase.