initial commit: Proximity iOS app proposal, full Swift code scaffold, reference backend, testing docs, generated Xcode project

Proximity/ViewModels/PresenceViewModel.swift

@@ -0,0 +1,60 @@
+import Foundation
+import Combine
+
+/// View model for the presence experience.
+///
+/// Exposes the state the UI needs to render the "am I present?" moment, the
+/// radius tier picker, and the live feed of encounters (silhouettes).
+@MainActor
+final class PresenceViewModel: ObservableObject {
+
+    @Published var isPresent: Bool = false
+    @Published var radiusTier: DistanceTier = .rightHere
+    @Published private(set) var activeEngines: Set<ProximityEngine> = []
+    @Published private(set) var encounters: [Encounter] = []
+    @Published private(set) var lastScan: Date?
+
+    private let engine: PresenceEngine
+    private var cancellables = Set<AnyCancellable>()
+
+    init(engine: PresenceEngine) {
+        self.engine = engine
+
+        engine.$isPresent
+            .assign(to: &$isPresent)
+        engine.$radiusTier
+            .assign(to: &$radiusTier)
+        engine.$activeEngines
+            .assign(to: &$activeEngines)
+        engine.$recentEncounters
+            .assign(to: &$encounters)
+        engine.$lastScan
+            .assign(to: &$lastScan)
+    }
+
+    // MARK: - User actions
+
+    func togglePresence() {
+        isPresent.toggle()
+        Task { await engine.setPresent(isPresent) }
+    }
+
+    func setRadius(_ tier: DistanceTier) {
+        radiusTier = tier
+        Task { await engine.setRadiusTier(tier) }
+    }
+
+    /// Send a "wave" to a silhouette — the first step toward mutual reveal.
+    func wave(to encounter: Encounter) {
+        // In production: POST /v1/wave with the encounter token.
+        Task {
+            await engine.wave(to: encounter)
+        }
+    }
+
+    func block(_ encounter: Encounter) {
+        Task {
+            await engine.block(encounter)
+        }
+    }
+}