Fix device picker not updating chart data (#109) (#110)

* Fix device picker not updating chart data on multi-computer dives

Three issues fixed:
1. Picker showed devices with only fingerprint links (no samples) —
   selecting them silently fell back to all samples. Now only devices
   with actual sample data appear in the picker.
2. PPO2Chart used onChange(of: samples.count) which missed device
   switches with equal sample counts. Changed to samples.cacheKey.
3. Added "All Computers" option to show combined data from all devices.

Closes #109

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Fix "All Computers" selection lost on data reload

The device picker reset selectedDeviceId on every loadDiveData call
when it was nil, but nil now means the user intentionally chose
"All Computers". Add a hasPickedDevice flag so the default device
is only set on first load, preserving the user's selection across
edit sheet dismissals and other refreshes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: shaheinm

Profundum/Profundum/Views/DiveDetailView.swift

@@ -12,9 +12,9 @@ struct DiveDetailView: View {
     @State private var showEditSheet = false
     @State private var loadedTeammateIds: [String] = []
     @State private var loadedEquipmentIds: [String] = []
-    @State private var sourceCount: Int = 0
     @State private var sourceDeviceMap: [String: String] = [:]
     @State private var selectedDeviceId: String?
+    @State private var hasPickedDevice = false
     @State private var surfaceIntervalSec: Int64?
     @State private var formulaResults: [(name: String, value: Double)] = []
     @State private var errorMessage: String?
@@ -65,6 +65,13 @@ struct DiveDetailView: View {
         samples.contains { $0.tankPressure1Bar != nil || $0.tankPressure2Bar != nil }
     }
 
+    /// Devices that actually have sample data for this dive.
+    /// Filters out devices linked only via fingerprint (skipped dives).
+    private var devicesWithSamples: [String: String] {
+        let sampleDeviceIds = Set(samples.compactMap(\.deviceId))
+        return sourceDeviceMap.filter { sampleDeviceIds.contains($0.key) }
+    }
+
     /// Samples filtered to the selected device for chart display.
     private var chartSamples: [DiveSample] {
         guard let deviceId = selectedDeviceId else { return samples }
@@ -238,10 +245,20 @@ struct DiveDetailView: View {
             // Tags row
             ScrollView(.horizontal, showsIndicators: false) {
                 HStack(spacing: 8) {
-                    if sourceCount > 1 {
+                    if devicesWithSamples.count > 1 {
                         Menu {
+                            Button {
+                                selectedDeviceId = nil
+                            } label: {
+                                if selectedDeviceId == nil {
+                                    Label("All Computers", systemImage: "checkmark")
+                                } else {
+                                    Text("All Computers")
+                                }
+                            }
+                            Divider()
                             ForEach(
-                                sourceDeviceMap.sorted(by: { $0.value < $1.value }),
+                                devicesWithSamples.sorted(by: { $0.value < $1.value }),
                                 id: \.key
                             ) { deviceId, name in
                                 Button {
@@ -255,7 +272,10 @@ struct DiveDetailView: View {
                                 }
                             }
                         } label: {
-                            Badge(text: "\(sourceCount) computers", color: .purple)
+                            Badge(
+                                text: "\(devicesWithSamples.count) computers",
+                                color: .purple
+                            )
                         }
                         .accessibilityLabel("Select source computer for chart")
                     }
@@ -729,9 +749,9 @@ struct DiveDetailView: View {
             loadedTeammateIds = detail.teammateIds
             loadedEquipmentIds = detail.equipmentIds
             sourceDeviceMap = detail.sourceDeviceMap
-            sourceCount = detail.sourceDeviceMap.count
-            if selectedDeviceId == nil {
+            if !hasPickedDevice {
                 selectedDeviceId = dive.deviceId
+                hasPickedDevice = true
             }
 
             let diveInput = DiveInput(
@@ -945,7 +965,7 @@ struct PPO2Chart: View {
         .onAppear {
             chartData = PPO2ChartData(samples: samples)
         }
-        .onChange(of: samples.count) { _, _ in
+        .onChange(of: samples.cacheKey) { _, _ in
             chartData = PPO2ChartData(samples: samples)
         }
     }