fix(apple-watch): Apple Health shows inflated distance for treadmill workouts (km written as miles) - #4798

Root cause

When a workout ends, the Apple Watch writes the total distance to HealthKit via WatchWorkoutTracking.stopWorkOut(). The value it writes comes from WorkoutTracking.distance, which is populated from WatchKitConnection.distance (Watch side) on every heart-rate tick. WatchKitConnection.distance (Watch side) is set from the WatchConnectivity reply that the iPhone sends back whenever the Watch pings it.

The bug is a unit mismatch in that reply value. Depending on which device is the QZ primary:

The Watch always wrote the received value with HKUnit.mile(), so in the iPad-primary scenario it was writing km as if they were miles. A 4.47 km run showed up as 4.47 mi in Apple Health instead of 2.78 mi.

Evidence from the debug log

The log for the reported session (iFIT_Xenon1, 30 min run) shows two interleaved local-network message streams:

SENDER=PHONE  ODO=0.000621371   (first sample: 1 m in miles, correctly converted by lockscreen)
...
SENDER=PAD    ODO=0.000173898   (Watch/iPad km stream starts ~9 s later)
SENDER=PAD    ODO=0.000620490
...
SENDER=PAD    ODO=4.478690      ← 4.47 km = 2.78 mi
SENDER=PHONE  ODO=4.478690      ← PHONE ODO overwritten to km after Connection.swift clobbers WatchKitConnection.distance

At workout end the Watch received 4.47 via WatchConnectivity and wrote HKQuantity(unit: .mile(), doubleValue: 4.47) → Apple Health displayed 4.4 mi instead of 2.78 mi.

Why SENDER=PAD must be kept

Connection.swift reading ODO from SENDER=PAD is intentional and correct: it is how a secondary device (phone/Watch) receives live distance from a primary QZ instance (iPad or another phone). Removing that line would break multi-device setups.

Fix

Standardise the iPhone→Watch WatchConnectivity channel to always carry km. The Watch does the single km→miles conversion at write time.

src/ios/lockscreen.mm — stop pre-converting in the iPhone; pass raw km:

// before
[h setDistanceWithDistance:distance * 0.621371];
// after
[h setDistanceWithDistance:distance];

watchkit Extension/WatchWorkoutTracking.swift — convert at the HealthKit write site:

// before
let miles = WorkoutTracking.distance
// after
let miles = WorkoutTracking.distance * 0.621371

With both changes every distance source (iPhone primary via lockscreen, iPad/multi-device primary via Connection.swift) arrives at the Watch in km, and the conversion to miles happens once, in the right place.

Test plan

• Solo iPhone + treadmill (iPhone primary): verify Apple Health distance matches QZ display
• iPad primary + iPhone companion + Apple Watch: verify Apple Health distance matches QZ display on iPad
• Cycling workout: verify distance is correct (same code path, distanceCycling quantity type)
• Walking/elliptical/rowing: verify distance is correct

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