Add six-channel mixer board face to Porta424 app

App/Sources/Models/MixerState.swift

@@ -0,0 +1,39 @@
+import Foundation
+
+/// Per-channel mixer state for the Porta424 six-channel board.
+///
+/// All continuous values are normalized `0...1`. `pan` follows the hardware
+/// convention where `0` is hard-left, `0.5` is center, and `1` is hard-right.
+/// EQ knobs are centered at `0.5` (flat); their detent snaps back to flat.
+struct ChannelState: Identifiable, Equatable, Sendable {
+    /// Channel number as printed on the chassis (1...6).
+    let id: Int
+
+    var trim: Double = 0.6
+    var eqHigh: Double = 0.5
+    var eqMid: Double = 0.5
+    var eqLow: Double = 0.5
+    var fx1Send: Double = 0.0
+    var fx2Send: Double = 0.0
+    var pan: Double = 0.5
+    var level: Double = 0.65   // channel fader
+    var source: ChannelSource = .line
+    var isArmed: Bool = false  // record-armed to the assigned tape track
+}
+
+/// Input source selection for a mixer channel.
+enum ChannelSource: String, Equatable, Sendable {
+    case mic = "MIC"
+    case line = "LINE"
+
+    mutating func toggle() {
+        self = (self == .mic) ? .line : .mic
+    }
+}
+
+extension Array where Element == ChannelState {
+    /// The standard six-channel Porta424 board, numbered 1...6.
+    static var defaultBoard: [ChannelState] {
+        (1...6).map { ChannelState(id: $0) }
+    }
+}

App/Sources/ViewModels/TapeDeckViewModel.swift

@@ -18,6 +18,10 @@ final class TapeDeckViewModel {
     var tapePosition: Double = 0     // 0...1
     var counterSeconds: Double = 0
 
+    /// Six-channel mixer board state. UI-side mixer parameters (trim, EQ, pan,
+    /// channel faders) that mirror the hardware front panel.
+    var channels: [ChannelState] = .defaultBoard
+
     var factoryPresets: [PresetItem] = []
     var userPresets: [PresetItem] = []
     var activePresetId: String?
@@ -127,6 +131,22 @@ final class TapeDeckViewModel {
         tapePosition = 0
     }
 
+    // MARK: - Mixer Controls
+
+    /// Toggle the record-arm state of a mixer channel by its index (0-based).
+    func toggleArm(channelIndex: Int) {
+        guard channels.indices.contains(channelIndex) else { return }
+        channels[channelIndex].isArmed.toggle()
+        HapticEngine.buttonPress()
+    }
+
+    /// Toggle a channel's input source between MIC and LINE.
+    func toggleSource(channelIndex: Int) {
+        guard channels.indices.contains(channelIndex) else { return }
+        channels[channelIndex].source.toggle()
+        HapticEngine.buttonPress()
+    }
+
     // MARK: - Counter String
 
     var counterString: String {