docs(train): Health Connect through Kotlin of our own (ADR 0030, D30)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0030-halkyon-train.md

@@ -1,6 +1,6 @@
 # ADR 0030: Halkyon Train, what it does and where its data comes from
 
-- **Status:** decided 27–28 Oct 2026, by the developer (D1–D29 below). The shell (D12)
+- **Status:** decided 27–28 Oct 2026, by the developer (D1–D30 below). The shell (D12)
   is built; recording (D13–D28) is built on Android, iOS waiting for a Mac; Health
   Connect (D29) comes next.
 - **Numbering:** 0025 is held by the federation draft (stashed), 0026–0029 by the .NET
@@ -473,6 +473,17 @@ Strava. What was found, 27 Oct:
   firmware, and new kinds of data (daily activity, sleep, 24/7 heart rate, Nightly
   Recharge) with synced models of their own; it is tried only with the band at hand.
   The intervals (D2) need neither.
+- **D30 Health Connect through Kotlin of our own** (recommended, the developer's; revises
+  D6's `health` package, as D26 revised D5): `androidx.health.connect:connect-client`
+  (Apache-2.0, AndroidX, no Play services) behind a channel of Train's, as the strap's.
+  The `health` package (13.3.2) lacks power, cadence, elevation gained, distance and
+  speed as records of their own, ties no heart rate to its session, has no changes API
+  (so each read would be a whole window read again) and sets no client record ID (so a
+  workout written again would be a second copy, not a replacement). Our own gets every
+  record type, the changes API, Train's workout ID as the client record ID (written
+  again replaces, deleted deletes) and each record's origin. Its logic is tested on the
+  JVM, the Dart side on a fake platform; Apple Health needs Swift of its own later,
+  as iOS waits for a Mac anyway (D25).
 
 ## Consequences