docs(train): Health Connect, written and read (ADR 0030, D31)

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–D30 below). The shell (D12)
+- **Status:** decided 27–28 Oct 2026, by the developer (D1–D31 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
@@ -484,6 +484,39 @@ Strava. What was found, 27 Oct:
   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).
+- **D31 Health Connect, from turning it on to the workouts** (the developer's; 28 Oct):
+  - *Turning it on*: a *Health Connect* row in the account sheet (Train has no settings
+    yet) opens a screen with two switches, both off: *Write my workouts* and *Read from
+    other apps*. They are this phone's, as Health Connect is, kept per person in their
+    folder (`health_connect.json`, with what was written and the changes token), not
+    synced. Each permission is asked as its switch is turned on. Built into Android from
+    14; below, the row says it needs the Health Connect app. `connect-client` 1.1.0, the
+    stable one. The rationale Health Connect asks for is a short screen of Train's,
+    linked from the system's permission dialog.
+  - *Writing*: every workout of the person this phone holds, synced and earlier ones too;
+    Train's workout ID is the record's client ID and a counter its version, so an edit
+    replaces and a deletion deletes; imported ones are never written back. As a workout
+    is saved, edited or deleted, and as the app opens (what a sync brought). The session
+    (type, name, notes, its pauses as pause segments), its route with altitude and
+    accuracy, heart rate, speed and the rower's watts as samples, distance and elevation
+    gained as totals. No calories (no weight, no energy model yet); stroke rate has no
+    type there.
+  - *Reading*: the screen lists each app that wrote workouts there (Gadgetbridge,
+    Christopeit Connect), each with its own switch, off, new ones appearing as they
+    write; Train's permissions are per type, the filtering by app its own. As the app
+    opens and comes to the front, through the changes token; nothing in the background.
+    Turning it on asks for the history too, so older than 30 days comes in; refused, the
+    last 30 days only. Each session becomes a workout of Train's own store (D7: sealed,
+    synced), named by its app, with the samples Health Connect holds for it (heart rate,
+    distance, power). Another app's route asks consent per session, so none comes by
+    itself: an imported workout's page offers *Bring in the track*. An imported one's
+    name and notes can be edited, and it can be deleted, remembered on this phone so it
+    doesn't come back. Doubles: a session mostly overlapping one of Train's own of the
+    same kind isn't added; where Train's has no heart rate, the other's is added to it,
+    otherwise it is left out. Weight and resting heart rate wait for what uses them
+    (calories, zones), with the synced model they need.
+  - No migration: an imported workout is a workout, its origin one more field of the
+    sealed, versioned payload.
 
 ## Consequences