feat(#28): SceneKit gamut viewer

- Add native .gam mesh parser and mesh model (GamutMeshParser, GamutMesh).
- Add GamutView / GamutViewModel with SceneKit, bundled sRGB.gam reference,
  and profile-gamut comparison.
- Wire Stage 5 "View Gamut" button and sidebar quick action.
- Extract a best-effort .gam mesh after colprof via Iccgamut in
  ProfileWorkflowViewModel, with artefact gating for the generated .gam.
- Add BinaryResolver.referenceGamut() for bundled reference gamuts.
- Add Milestone6GamutUITests and GamutMeshParserTests.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Packages/ICCeryCore/Sources/ICCeryCore/Argyll/BinaryResolver.swift

@@ -88,9 +88,10 @@ public struct BinaryResolver: Sendable {
 
     /// Bundled reference gamut (`Resources/Argyll/reference_gamuts/`).
     public func referenceGamut(_ name: String) -> URL {
-        bundledRoot
+        let stem = name.hasSuffix(".gam") ? name : "\(name).gam"
+        return bundledRoot
             .appendingPathComponent("reference_gamuts", isDirectory: true)
-            .appendingPathComponent(name, isDirectory: false)
+            .appendingPathComponent(stem, isDirectory: false)
     }
 
     /// Whether the resolved path exists and is executable.

Packages/ICCeryCore/Sources/ICCeryCore/Files/ArtefactProbe.swift

@@ -12,19 +12,23 @@ public struct StageArtefacts: Sendable, Equatable {
     public var stage4Complete = false
     /// Absolute path of the profile file when present.
     public var profilePath: URL?
+    /// Absolute path of the `.gam` gamut mesh when present (issue #28).
+    public var gamPath: URL?
 
     public init(
         stage1Complete: Bool = false,
         stage2Complete: Bool = false,
         stage3Complete: Bool = false,
         stage4Complete: Bool = false,
-        profilePath: URL? = nil
+        profilePath: URL? = nil,
+        gamPath: URL? = nil
     ) {
         self.stage1Complete = stage1Complete
         self.stage2Complete = stage2Complete
         self.stage3Complete = stage3Complete
         self.stage4Complete = stage4Complete
         self.profilePath = profilePath
+        self.gamPath = gamPath
     }
 }
 
@@ -45,6 +49,10 @@ public enum ArtefactProbe {
         if let profile = resolveProfile(basename: basename, cwd: cwd, fileManager: fileManager) {
             out.stage4Complete = true
             out.profilePath = profile
+            let gam = artefact(basename, "gam", cwd)
+            if exists(gam, fm: fileManager) {
+                out.gamPath = gam
+            }
         }
         return out
     }

Packages/ICCeryCore/Sources/ICCeryCore/Gamut/GamutMesh.swift

@@ -0,0 +1,51 @@
+import Foundation
+import simd
+
+/// A single vertex of an Argyll `.gam` surface mesh.
+///
+/// Coordinates follow the v0.8.5 SceneKit convention: `x = a*`, `y = L*`,
+/// `z = b*` so that the a* (green-red) axis is horizontal, L* (lightness)
+/// is vertical, and b* (blue-yellow) is depth.
+public struct GamutVertex: Sendable, Equatable {
+    public let lab: LabColor
+    public let rgb: DisplayRGB
+    public let position: SIMD3<Float>
+
+    public init(lab: LabColor, rgb: DisplayRGB) {
+        self.lab = lab
+        self.rgb = rgb
+        self.position = SIMD3<Float>(Float(lab.a), Float(lab.l), Float(lab.b))
+    }
+}
+
+/// A face from an Argyll `.gam` file.
+///
+/// Indices are 0-based and index into `GamutMesh.vertices` in the order the
+/// vertices were pushed by the parser (the `VERTEX_NO` column is discarded).
+public struct GamutTriangle: Sendable, Equatable {
+    public let a: UInt32
+    public let b: UInt32
+    public let c: UInt32
+
+    public init(a: UInt32, b: UInt32, c: UInt32) {
+        self.a = a
+        self.b = b
+        self.c = c
+    }
+}
+
+/// Parsed gamut surface mesh.
+public struct GamutMesh: Sendable, Equatable {
+    public let vertices: [GamutVertex]
+    public let faces: [GamutTriangle]
+
+    public init(vertices: [GamutVertex], faces: [GamutTriangle]) {
+        self.vertices = vertices
+        self.faces = faces
+    }
+
+    /// A printable summary for diagnostics.
+    public var summary: String {
+        "GamutMesh(vertices: \(vertices.count), faces: \(faces.count))"
+    }
+}

Packages/ICCeryCore/Sources/ICCeryCore/Gamut/GamutMeshParser.swift

@@ -0,0 +1,152 @@
+import Foundation
+
+/// Errors thrown by ``GamutMeshParser``.
+public enum GamutMeshParseError: LocalizedError, Equatable, Sendable {
+    case missingFile
+    case readFailed(underlying: String)
+    case emptyFile
+    case noDataBlock
+    case malformedVertexLine(line: Int, content: String)
+    case malformedFaceLine(line: Int, content: String)
+    case outOfBoundsVertexIndex(UInt32, max: UInt32)
+    case invalidLabPlausibility(line: Int, content: String)
+
+    public var errorDescription: String? {
+        switch self {
+        case .missingFile:
+            return "Gamut file not found."
+        case .readFailed(let reason):
+            return "Could not read gamut file: \(reason)"
+        case .emptyFile:
+            return "Gamut file is empty."
+        case .noDataBlock:
+            return "Gamut file contains no BEGIN_DATA blocks."
+        case .malformedVertexLine(let line, let content):
+            return "Malformed vertex on line \(line): \(content)"
+        case .malformedFaceLine(let line, let content):
+            return "Malformed face on line \(line): \(content)"
+        case .outOfBoundsVertexIndex(let index, let max):
+            return "Face references vertex \(index) but only \(max + 1) vertices exist."
+        case .invalidLabPlausibility(let line, let content):
+            return "Lab value outside plausible range on line \(line): \(content)"
+        }
+    }
+}
+
+/// Parses Argyll `.gam` ASCII files into ``GamutMesh``.
+///
+/// The parser recognises two `BEGIN_DATA` … `END_DATA` blocks:
+///
+/// 1. Vertices: `VERTEX_NO LAB_L LAB_A LAB_B`
+/// 2. Faces:    `VERTEX_0 VERTEX_1 VERTEX_2` (0-based indices)
+///
+/// Lines beginning with `#` and blank lines are ignored.  `BEGIN_DATA` and
+/// `END_DATA` are matched case-insensitively.  The `VERTEX_NO` column is
+/// discarded; vertices are indexed in push order, matching Argyll's output.
+public enum GamutMeshParser {
+
+    /// Parse the file at `url`.
+    public static func parse(url: URL) throws -> GamutMesh {
+        guard FileManager.default.fileExists(atPath: url.path) else {
+            throw GamutMeshParseError.missingFile
+        }
+        guard let data = FileManager.default.contents(atPath: url.path) else {
+            throw GamutMeshParseError.readFailed(underlying: "contents(atPath:) returned nil")
+        }
+        guard let text = String(data: data, encoding: .utf8) ?? String(data: data, encoding: .ascii),
+              !text.isEmpty else {
+            throw GamutMeshParseError.emptyFile
+        }
+        return try parse(text: text)
+    }
+
+    /// Parse raw `.gam` text.
+    public static func parse(text: String) throws -> GamutMesh {
+        var vertices: [GamutVertex] = []
+        var faces: [GamutTriangle] = []
+
+        var dataBlock = 0
+        var inData = false
+        var lineNumber = 0
+        var warnings: [String] = []
+
+        for rawLine in text.components(separatedBy: .newlines) {
+            lineNumber += 1
+
+            // Strip inline `#` comments before any other processing.
+            let uncommented = rawLine.split(separator: "#", maxSplits: 1).first.map(String.init) ?? ""
+            let trimmed = uncommented.trimmingCharacters(in: .whitespacesAndNewlines)
+            guard !trimmed.isEmpty else { continue }
+
+            let upper = trimmed.uppercased()
+
+            if upper == "BEGIN_DATA" {
+                dataBlock += 1
+                inData = true
+                continue
+            }
+            if upper == "END_DATA" {
+                inData = false
+                continue
+            }
+
+            if !inData { continue }
+
+            let parts = trimmed.components(separatedBy: .whitespaces)
+                .filter { !$0.isEmpty }
+                .compactMap(Double.init)
+
+            guard !parts.isEmpty else { continue }
+
+            if dataBlock == 1 {
+                // Vertex format: index L a b
+                guard parts.count >= 4 else {
+                    warnings.append("vertex arity \(parts.count) on line \(lineNumber)")
+                    continue
+                }
+                let l = parts[1]
+                let a = parts[2]
+                let b = parts[3]
+
+                if l < 0 || l > 100 || abs(a) > 128 || abs(b) > 128 {
+                    warnings.append("Lab plausibility warning on line \(lineNumber): L=\(l) a=\(a) b=\(b)")
+                    // We still keep the vertex; Argyll can exceed ±128.
+                }
+
+                let lab = LabColor(l: l, a: a, b: b)
+                let rgb = LabColorMath.labToSRGB(lab)
+                vertices.append(GamutVertex(lab: lab, rgb: rgb))
+            } else {
+                // Face format: v0 v1 v2 (can extend for future n-gons, take first 3)
+                guard parts.count >= 3 else {
+                    warnings.append("face arity \(parts.count) on line \(lineNumber)")
+                    continue
+                }
+                let idx = parts.prefix(3).compactMap { UInt32(exactly: $0) }
+                guard idx.count == 3 else {
+                    warnings.append("non-integer face indices on line \(lineNumber)")
+                    continue
+                }
+                faces.append(GamutTriangle(a: idx[0], b: idx[1], c: idx[2]))
+            }
+        }
+
+        // Trim out-of-bounds face indices instead of throwing, so a slightly
+        // malformed file still renders.  This matches the Web viewer's
+        // forgiving posture while surfacing the obvious cases.
+        let validFaces = faces.filter { face in
+            let max = UInt32(vertices.count)
+            guard face.a < max, face.b < max, face.c < max else {
+                warnings.append("dropping face \(face) referencing missing vertex")
+                return false
+            }
+            return true
+        }
+
+        if dataBlock == 0 {
+            throw GamutMeshParseError.noDataBlock
+        }
+
+        return GamutMesh(vertices: vertices, faces: validFaces)
+    }
+}

Sources/ICCery/GamutView.swift

@@ -0,0 +1,435 @@
+import SwiftUI
+import SceneKit
+import ICCeryCore
+import simd
+
+/// Native SceneKit 3D gamut viewer.
+///
+/// Displays a profile gamut mesh and the bundled `sRGB.gam` reference.  Uses
+/// the CIELAB coordinate convention `x = a*`, `y = L*`, `z = b*` so that the
+/// a* (green-red) axis is horizontal, L* (lightness) is vertical, and b*
+/// (blue-yellow) is depth.
+struct GamutView: View {
+    @State private var viewModel: GamutViewModel
+    @FocusState private var isFocused: Bool
+
+    init(profileGamURL: URL? = nil) {
+        _viewModel = State(wrappedValue: GamutViewModel(profileGamURL: profileGamURL))
+    }
+
+    var body: some View {
+        ZStack {
+            GamutSceneView(
+                profileMesh: viewModel.profileMesh,
+                referenceMesh: viewModel.sRGBMesh,
+                onReset: $viewModel.resetCamera
+            )
+            .focusable()
+            .focused($isFocused)
+            .focusEffectDisabled()
+            .onKeyPress(.init("R"), action: {
+                viewModel.resetCamera()
+                return .handled
+            })
+            .onAppear { isFocused = true }
+
+            VStack {
+                HStack {
+                    Spacer()
+                    Button(action: { viewModel.resetCamera() }) {
+                        Text("Reset view")
+                    }
+                    .accessibilityIdentifier("btnResetGamutCamera")
+                    .padding(8)
+                }
+                Spacer()
+                HStack {
+                    Text(viewModel.status)
+                        .font(.caption)
+                        .padding(8)
+                        .background(.thinMaterial)
+                        .cornerRadius(6)
+                        .accessibilityIdentifier("gamutStatusText")
+                    Spacer()
+                }
+                .padding(8)
+            }
+        }
+        .frame(minWidth: 500, minHeight: 400)
+        .accessibilityElement(children: .contain)
+        .accessibilityIdentifier("gamutView")
+    }
+}
+
+/// `NSViewRepresentable` wrapper around an `SCNView` that builds the scene from
+/// one or two ``GamutMesh`` values.
+///
+/// Scene construction and camera reset are coordinated through a typed callback
+/// binding owned by the view model.
+private struct GamutSceneView: NSViewRepresentable {
+    var profileMesh: GamutMesh?
+    var referenceMesh: GamutMesh?
+    var onReset: Binding<() -> Void>
+
+    func makeNSView(context: Context) -> SCNView {
+        let scnView = SCNView()
+        scnView.backgroundColor = NSColor(red: 0.055, green: 0.055, blue: 0.078, alpha: 1)
+        scnView.allowsCameraControl = true
+        scnView.showsStatistics = false
+        scnView.antialiasingMode = .multisampling4X
+
+        let scene = SCNScene()
+        scnView.scene = scene
+        scnView.autoenablesDefaultLighting = false
+
+        context.coordinator.scnView = scnView
+        context.coordinator.scene = scene
+        context.coordinator.buildScene(profile: profileMesh, reference: referenceMesh)
+
+        return scnView
+    }
+
+    func updateNSView(_ nsView: SCNView, context: Context) {
+        context.coordinator.buildScene(profile: profileMesh, reference: referenceMesh)
+    }
+
+    func makeCoordinator() -> Coordinator {
+        let coordinator = Coordinator()
+        onReset.wrappedValue = { [weak coordinator] in
+            coordinator?.resetCamera()
+        }
+        return coordinator
+    }
+
+    @MainActor
+    final class Coordinator: NSObject {
+        weak var scnView: SCNView?
+        weak var scene: SCNScene?
+
+        private let profileNode = SCNNode()
+        private let referenceGroup = SCNNode()
+        private let axisNode = SCNNode()
+        private let cameraNode: SCNNode = {
+            let node = SCNNode()
+            node.camera = SCNCamera()
+            node.camera?.zFar = 2000
+            return node
+        }()
+
+        func buildScene(profile: GamutMesh?, reference: GamutMesh?) {
+            guard let scene else { return }
+
+            // Rebuild from scratch on every mesh change to avoid stale geometry.
+            scene.rootNode.childNodes.forEach { $0.removeFromParentNode() }
+            scene.rootNode.addChildNode(axisNode)
+            scene.rootNode.addChildNode(profileNode)
+            scene.rootNode.addChildNode(referenceGroup)
+            scene.rootNode.addChildNode(cameraNode)
+
+            buildAxisScaffold()
+
+            if let profile {
+                profileNode.addChildNode(profileMeshNode(profile, name: "profile"))
+            } else {
+                profileNode.childNodes.forEach { $0.removeFromParentNode() }
+            }
+
+            if let reference {
+                referenceGroup.childNodes.forEach { $0.removeFromParentNode() }
+                referenceGroup.addChildNode(referenceMeshNode(reference))
+            }
+
+            addLights(to: scene)
+            resetCamera()
+        }
+
+        private func addLights(to scene: SCNScene) {
+            let ambient = SCNNode()
+            ambient.light = SCNLight()
+            ambient.light?.type = .ambient
+            ambient.light?.color = NSColor.white
+            ambient.light?.intensity = 750
+            scene.rootNode.addChildNode(ambient)
+
+            let key = SCNNode()
+            key.light = SCNLight()
+            key.light?.type = .directional
+            key.light?.color = NSColor.white
+            key.light?.intensity = 800
+            key.position = SCNVector3(150, 250, 150)
+            key.look(at: SCNVector3(0, 50, 0))
+            scene.rootNode.addChildNode(key)
+
+            let fill = SCNNode()
+            fill.light = SCNLight()
+            fill.light?.type = .directional
+            fill.light?.color = NSColor.white
+            fill.light?.intensity = 350
+            fill.position = SCNVector3(-120, -80, -120)
+            fill.look(at: SCNVector3(0, 50, 0))
+            scene.rootNode.addChildNode(fill)
+        }
+
+        private func buildAxisScaffold() {
+            axisNode.childNodes.forEach { $0.removeFromParentNode() }
+
+            // Bounding box: a*,b* ±128, L* 0–100.
+            let box = buildWireBox(size: SIMD3<Float>(256, 100, 256), color: NSColor(red: 0.137, green: 0.137, blue: 0.212, alpha: 0.9))
+            box.position = SCNVector3(0, 50, 0)
+            axisNode.addChildNode(box)
+
+            // Ground grid at y=0.
+            axisNode.addChildNode(buildGridNode())
+
+            // Axis lines.
+            axisNode.addChildNode(buildLineNode(
+                from: SIMD3<Float>(0, 0, 0),
+                to: SIMD3<Float>(0, 100, 0),
+                color: NSColor(red: 0.8, green: 0.8, blue: 0.8, alpha: 1.0)
+            ))
+            let abAxisColor = NSColor(red: 0.6, green: 0.733, blue: 0.8, alpha: 1.0)
+            axisNode.addChildNode(buildLineNode(
+                from: SIMD3<Float>(-128, 0, 0),
+                to: SIMD3<Float>(128, 0, 0),
+                color: abAxisColor
+            ))
+            axisNode.addChildNode(buildLineNode(
+                from: SIMD3<Float>(0, 0, -128),
+                to: SIMD3<Float>(0, 0, 128),
+                color: abAxisColor
+            ))
+        }
+
+        private func buildWireBox(size: SIMD3<Float>, color: NSColor) -> SCNNode {
+            let hx = size.x / 2
+            let hy = size.y / 2
+            let hz = size.z / 2
+
+            let corners: [SIMD3<Float>] = [
+                SIMD3(-hx, -hy, -hz), SIMD3(hx, -hy, -hz),
+                SIMD3(hx, -hy, hz), SIMD3(-hx, -hy, hz),
+                SIMD3(-hx, hy, -hz), SIMD3(hx, hy, -hz),
+                SIMD3(hx, hy, hz), SIMD3(-hx, hy, hz),
+            ]
+
+            // 12 edges, two vertices each.
+            let edges: [(Int, Int)] = [
+                (0,1), (1,2), (2,3), (3,0),
+                (4,5), (5,6), (6,7), (7,4),
+                (0,4), (1,5), (2,6), (3,7),
+            ]
+
+            var points: [SIMD3<Float>] = []
+            for (a, b) in edges {
+                points.append(corners[a])
+                points.append(corners[b])
+            }
+
+            return lineNode(points: points, color: color)
+        }
+
+        private func buildGridNode() -> SCNNode {
+            let divisions = 16
+            let half = Float(128)
+            let step = (half * 2) / Float(divisions)
+
+            var points: [SIMD3<Float>] = []
+            for i in 0...divisions {
+                let v = -half + step * Float(i)
+                // X-aligned
+                points.append(SIMD3(-half, 0, v))
+                points.append(SIMD3(half, 0, v))
+                // Z-aligned
+                points.append(SIMD3(v, 0, -half))
+                points.append(SIMD3(v, 0, half))
+            }
+
+            let gridColor = NSColor(red: 0.118, green: 0.118, blue: 0.157, alpha: 1.0)
+            return lineNode(points: points, color: gridColor)
+        }
+
+        private func buildLineNode(from: SIMD3<Float>, to: SIMD3<Float>, color: NSColor) -> SCNNode {
+            return lineNode(points: [from, to], color: color)
+        }
+
+        /// Builds a line-set from a flat list of point pairs.
+        ///
+        /// Uses data-backed `SCNGeometrySource` so it works with `simd` vectors
+        /// and avoids the SceneKit convenience-initializer label mismatch.
+        private func lineNode(points: [SIMD3<Float>], color: NSColor) -> SCNNode {
+            let source = source(for: points)
+
+            let count = points.count
+            var indices: [UInt32] = []
+            indices.reserveCapacity(count)
+            for i in 0..<UInt32(count) {
+                indices.append(i)
+            }
+            let data = indices.withUnsafeBytes { Data($0) }
+            let element = SCNGeometryElement(
+                data: data,
+                primitiveType: .line,
+                primitiveCount: count / 2,
+                bytesPerIndex: 4
+            )
+
+            let geometry = SCNGeometry(sources: [source], elements: [element])
+            let material = SCNMaterial()
+            material.lightingModel = .constant
+            material.diffuse.contents = color
+            material.isDoubleSided = false
+            geometry.materials = [material]
+
+            return SCNNode(geometry: geometry)
+        }
+
+        private func profileMeshNode(_ mesh: GamutMesh, name: String) -> SCNNode {
+            let (geometry, _) = scnGeometry(for: mesh)
+
+            let material = SCNMaterial()
+            material.lightingModel = .lambert
+            material.diffuse.contents = NSColor.white
+            material.transparency = 0.88
+            material.isDoubleSided = true
+            geometry.materials = [material]
+
+            let node = SCNNode(geometry: geometry)
+            node.name = name
+            return node
+        }
+
+        private func referenceMeshNode(_ mesh: GamutMesh) -> SCNNode {
+            let (geometry, _) = scnGeometry(for: mesh)
+
+            // Faint fill.
+            let fillMaterial = SCNMaterial()
+            fillMaterial.lightingModel = .lambert
+            fillMaterial.diffuse.contents = NSColor(red: 0.533, green: 0.6, blue: 0.733, alpha: 1.0)
+            fillMaterial.transparency = 0.93
+            fillMaterial.isDoubleSided = true
+            fillMaterial.writesToDepthBuffer = false
+            geometry.materials = [fillMaterial]
+
+            let fillNode = SCNNode(geometry: geometry)
+
+            // Structural outline: one line per triangle edge.
+            var linePoints: [SIMD3<Float>] = []
+            for face in mesh.faces {
+                let va = mesh.vertices[Int(face.a)].position
+                let vb = mesh.vertices[Int(face.b)].position
+                let vc = mesh.vertices[Int(face.c)].position
+                linePoints.append(va); linePoints.append(vb)
+                linePoints.append(vb); linePoints.append(vc)
+                linePoints.append(vc); linePoints.append(va)
+            }
+
+            let edgeColor = NSColor(red: 0.4, green: 0.533, blue: 0.667, alpha: 0.55)
+            let edgeNode = lineNode(points: linePoints, color: edgeColor)
+
+            let group = SCNNode()
+            group.addChildNode(fillNode)
+            group.addChildNode(edgeNode)
+            return group
+        }
+
+        /// Returns an `SCNGeometry` with per-vertex positions and sRGB colours.
+        ///
+        /// Uses data-backed `SCNGeometrySource` initializers; this is the only
+        /// path that supports vertex colours through the `.color` semantic.
+        private func scnGeometry(for mesh: GamutMesh) -> (SCNGeometry, SCNGeometryElement) {
+            let positions = mesh.vertices.map { $0.position }
+            let positionData = positions.withUnsafeBytes { Data($0) }
+            let positionSource = SCNGeometrySource(
+                data: positionData,
+                semantic: .vertex,
+                vectorCount: positions.count,
+                usesFloatComponents: true,
+                componentsPerVector: 3,
+                bytesPerComponent: MemoryLayout<Float>.size,
+                dataOffset: 0,
+                dataStride: MemoryLayout<SIMD3<Float>>.stride
+            )
+
+            let colors: [SIMD4<Float>] = mesh.vertices.map { v in
+                SIMD4<Float>(Float(v.rgb.r), Float(v.rgb.g), Float(v.rgb.b), 1.0)
+            }
+            let colorData = colors.withUnsafeBytes { Data($0) }
+            let colorSource = SCNGeometrySource(
+                data: colorData,
+                semantic: .color,
+                vectorCount: colors.count,
+                usesFloatComponents: true,
+                componentsPerVector: 4,
+                bytesPerComponent: MemoryLayout<Float>.size,
+                dataOffset: 0,
+                dataStride: MemoryLayout<SIMD4<Float>>.stride
+            )
+
+            var indices: [UInt32] = []
+            indices.reserveCapacity(mesh.faces.count * 3)
+            for face in mesh.faces {
+                indices.append(face.a)
+                indices.append(face.b)
+                indices.append(face.c)
+            }
+            let data = indices.withUnsafeBytes { Data($0) }
+            let element = SCNGeometryElement(
+                data: data,
+                primitiveType: .triangles,
+                primitiveCount: mesh.faces.count,
+                bytesPerIndex: 4
+            )
+
+            let geometry = SCNGeometry(sources: [positionSource, colorSource], elements: [element])
+            return (geometry, element)
+        }
+
+        /// Shared helper for data-backed position sources.
+        private func source(for points: [SIMD3<Float>]) -> SCNGeometrySource {
+            let data = points.withUnsafeBytes { Data($0) }
+            return SCNGeometrySource(
+                data: data,
+                semantic: .vertex,
+                vectorCount: points.count,
+                usesFloatComponents: true,
+                componentsPerVector: 3,
+                bytesPerComponent: MemoryLayout<Float>.size,
+                dataOffset: 0,
+                dataStride: MemoryLayout<SIMD3<Float>>.stride
+            )
+        }
+
+        func resetCamera() {
+            guard let scnView else { return }
+
+            // Re-create the camera node so `allowsCameraControl` starts from the
+            // canonical home position every time.
+            let newCameraNode = SCNNode()
+            newCameraNode.camera = SCNCamera()
+            newCameraNode.camera?.zFar = 2000
+
+            let eye = SIMD3<Float>(180, 120, 180)
+            let target = SIMD3<Float>(0, 50, 0)
+            newCameraNode.simdTransform = lookAt(eye: eye, target: target, up: SIMD3<Float>(0, 1, 0))
+
+            if let scene = scnView.scene, scene.rootNode.childNodes.contains(cameraNode) {
+                cameraNode.removeFromParentNode()
+            }
+            scnView.scene?.rootNode.addChildNode(newCameraNode)
+            scnView.pointOfView = newCameraNode
+        }
+
+        private func lookAt(eye: SIMD3<Float>, target: SIMD3<Float>, up: SIMD3<Float>) -> simd_float4x4 {
+            let forward = normalize(target - eye)
+            let right = normalize(cross(up, forward))
+            let newUp = cross(forward, right)
+
+            var matrix = simd_float4x4()
+            matrix.columns.0 = SIMD4<Float>(right, 0)
+            matrix.columns.1 = SIMD4<Float>(newUp, 0)
+            matrix.columns.2 = SIMD4<Float>(-forward, 0)
+            matrix.columns.3 = SIMD4<Float>(eye, 1)
+            return matrix
+        }
+    }
+}

Sources/ICCery/GamutViewModel.swift

@@ -0,0 +1,57 @@
+import Foundation
+import ICCeryCore
+import Observation
+
+/// View model for the native SceneKit gamut viewer.
+///
+/// Loads the bundled `sRGB.gam` reference immediately and, optionally, a
+/// printer/profile `.gam` from the current working directory.
+@MainActor
+@Observable
+final class GamutViewModel {
+
+    /// Parsed reference sRGB gamut mesh.
+    var sRGBMesh: GamutMesh?
+
+    /// Parsed printer/profile gamut mesh.
+    var profileMesh: GamutMesh?
+
+    /// User-facing status line.
+    var status = "Loading gamut…"
+
+    /// Closure injected into the SceneKit view to request a camera reset.
+    var resetCamera: () -> Void = {}
+
+    private let profileGamURL: URL?
+
+    init(profileGamURL: URL? = nil) {
+        self.profileGamURL = profileGamURL
+        Task { await load() }
+    }
+
+    private func load() async {
+        do {
+            let referenceURL = BinaryResolver().referenceGamut("sRGB")
+            let reference = try await parse(url: referenceURL)
+            sRGBMesh = reference
+
+            if let profileGamURL {
+                let profile = try await parse(url: profileGamURL)
+                profileMesh = profile
+                status = "Profile gamut (\(profile.faces.count) faces) vs sRGB reference"
+            } else {
+                status = "sRGB reference gamut (\(reference.faces.count) faces)"
+            }
+        } catch {
+            status = "Could not load gamut: \(error.localizedDescription)"
+        }
+    }
+
+    /// Parses a `.gam` file off the main actor so large meshes do not stall
+    /// the UI.
+    private func parse(url: URL) async throws -> GamutMesh {
+        try await Task.detached {
+            try GamutMeshParser.parse(url: url)
+        }.value
+    }
+}

Sources/ICCery/ProfileWorkflowViewModel.swift

@@ -52,6 +52,8 @@ final class ProfileWorkflowViewModel {
     var colprofProgress: String?
     var lastError: String?
     var createdProfileURL: URL?
+    /// Path to the `.gam` gamut mesh extracted post-`colprof` (issue #28).
+    var createdGamutURL: URL?
 
     // MARK: - Stage 4/5 calibration (issue #24)
 
@@ -84,12 +86,17 @@ final class ProfileWorkflowViewModel {
         restoreCreatedProfileURL()
     }
 
-    /// Restores `createdProfileURL` from the wizard artefacts or by probing
+    /// Restores `createdProfileURL` and `createdGamutURL` from the wizard
-    /// the working directory for an existing `.icc`/`.icm` (#52).
+    /// artefacts or by probing the working directory (#52, #28).
     func restoreCreatedProfileURL() {
         let cwd = wizard.effectiveWorkingDirectory ?? PathSecurity.resolveSafeCwd(nil)
         createdProfileURL = wizard.artefacts.profilePath
             ?? ArtefactProbe.resolveProfile(basename: wizard.basename, cwd: cwd)
+        createdGamutURL = wizard.artefacts.gamPath
+            ?? ArtefactProbe.artefact(wizard.basename, "gam", cwd)
+        if let gam = createdGamutURL, !FileManager.default.fileExists(atPath: gam.path) {
+            createdGamutURL = nil
+        }
     }
 
     // MARK: - Derived
@@ -190,6 +197,7 @@ final class ProfileWorkflowViewModel {
         colprofProgress = nil
         lastError = nil
         createdProfileURL = nil
+        createdGamutURL = nil
 
         let runner = environment.runner
         Task { @MainActor [weak self] in
@@ -223,12 +231,13 @@ final class ProfileWorkflowViewModel {
                 // Gamut extraction is best-effort for Stage 5 / M6 viewer.
                 do {
                     let gamConfig = IccgamutConfig(profileURL: finalProfileURL)
-                    _ = try await runner.runIccgamut(config: gamConfig) { [weak self] batch in
+                    let gamURL = try await runner.runIccgamut(config: gamConfig) { [weak self] batch in
                         Task { @MainActor [weak self] in
                             self?.colprofLog.append(contentsOf: batch)
                         }
                     }
-                    self.colprofLog.append("Gamut mesh extracted.")
+                    self.createdGamutURL = gamURL
+                    self.colprofLog.append("Gamut mesh extracted: \(gamURL.lastPathComponent)")
                 } catch {
                     self.wizard.showNotice(
                         "Gamut extraction skipped: \(error.localizedDescription)",

Sources/ICCery/RootView.swift

@@ -53,6 +53,9 @@ struct RootView: View {
         .sheet(isPresented: $showingAbout) {
             AboutView { showingAbout = false }
         }
+        .sheet(isPresented: $workflow.wizard.showingGamutViewer) {
+            GamutView(profileGamURL: workflow.wizard.gamutProfileURL)
+        }
     }
 
     @ViewBuilder

Sources/ICCery/SidebarView.swift

@@ -84,6 +84,14 @@ struct SidebarView: View {
             .disabled(true)
             .padding(.horizontal, 12)
 
+            Button(action: { model.openGamut(profileGamURL: workflow.profile.createdGamutURL) }) {
+                Label("View Gamut", systemImage: "view.3d")
+                    .frame(maxWidth: .infinity)
+            }
+            .controlSize(.large)
+            .accessibilityIdentifier("btnViewGamut")
+            .padding(.horizontal, 12)
+
             Divider().overlay(Theme.border)
                 .padding(.vertical, 8)
 

Sources/ICCery/Stage5View.swift

@@ -146,6 +146,12 @@ struct Stage5View: View {
 
                 Spacer()
 
+                Button("View Gamut") {
+                    model.wizard.openGamut(profileGamURL: model.createdGamutURL)
+                }
+                .disabled(model.createdGamutURL == nil)
+                .accessibilityIdentifier("btnViewGamut")
+
                 Button("Install Profile") { model.beginInstallProfile() }
                     .disabled(model.createdProfileURL == nil)
                     .accessibilityIdentifier("btnInstallProfile")

Sources/ICCery/WizardViewModel.swift

@@ -42,6 +42,10 @@ final class WizardViewModel {
     var notice: Notice?
     /// Current artefact probe result; recomputed on `refreshGating()`.
     private(set) var artefacts = StageArtefacts()
+    /// Whether the 3D gamut viewer sheet is open (issue #28).
+    var showingGamutViewer = false
+    /// Optional `.gam` URL to show alongside the sRGB reference.
+    var gamutProfileURL: URL?
 
     private let stateStore: WizardStateStore
     private var noticeDismissTask: Task<Void, Never>?
@@ -126,6 +130,12 @@ final class WizardViewModel {
         stage = .generate
     }
 
+    /// Open the 3D gamut viewer (issue #28).
+    func openGamut(profileGamURL: URL? = nil) {
+        self.gamutProfileURL = profileGamURL
+        showingGamutViewer = true
+    }
+
     /// Window-focus hook (#151): files deleted in Finder re-lock stages.
     /// If the current stage re-locked, fall back to the deepest unlocked.
     func windowDidBecomeKey() {

Tests/ICCeryCoreTests/GamutMeshParserTests.swift

@@ -0,0 +1,166 @@
+import Foundation
+import Testing
+@testable import ICCeryCore
+
+/// ``GamutMeshParser`` acceptance + edge-case tests.
+@Suite("Gamut mesh parser")
+struct GamutMeshParserTests {
+
+    /// Returns the bundled real `sRGB.gam` in `Resources/Argyll/reference_gamuts`.
+    private var bundledSRGBGamURL: URL {
+        let bundle = Bundle.main
+        let resource = bundle.resourceURL ?? bundle.bundleURL
+        return resource.appendingPathComponent("Argyll/reference_gamuts/sRGB.gam")
+    }
+
+    @Test("Parses bundled sRGB.gam")
+    func parsesBundledSRGB() throws {
+        let mesh = try GamutMeshParser.parse(url: bundledSRGBGamURL)
+
+        #expect(mesh.vertices.count == 448, "sRGB.gam has 448 vertices")
+        #expect(mesh.faces.count == 892, "sRGB.gam has 892 faces")
+    }
+
+    @Test("Discards VERTEX_NO and uses push-order indices")
+    func discardsVertexNo() throws {
+        let text = """
+        GAMUT
+        NUMBER_OF_FIELDS 4
+        BEGIN_DATA_FORMAT
+        VERTEX_NO LAB_L LAB_A LAB_B
+        END_DATA_FORMAT
+        NUMBER_OF_SETS 4
+        BEGIN_DATA
+        100 10.0 20.0 30.0
+        50  20.0 30.0 40.0
+        2   30.0 40.0 50.0
+        7   40.0 50.0 60.0
+        END_DATA
+        NUMBER_OF_FIELDS 3
+        BEGIN_DATA_FORMAT
+        VERTEX_0 VERTEX_1 VERTEX_2
+        END_DATA_FORMAT
+        NUMBER_OF_SETS 2
+        BEGIN_DATA
+        0 1 2
+        1 2 3
+        END_DATA
+        """
+
+        let mesh = try GamutMeshParser.parse(text: text)
+
+        #expect(mesh.vertices.count == 4)
+        #expect(mesh.faces.count == 2)
+        #expect(mesh.vertices[0].lab == LabColor(l: 10, a: 20, b: 30))
+        #expect(mesh.vertices[3].lab == LabColor(l: 40, a: 50, b: 60))
+    }
+
+    @Test("Ignores comments and blank lines")
+    func ignoresComments() throws {
+        let text = """
+        # Header comment
+        NUMBER_OF_FIELDS 4
+        BEGIN_DATA_FORMAT
+        VERTEX_NO LAB_L LAB_A LAB_B
+        END_DATA_FORMAT
+        NUMBER_OF_SETS 2
+        BEGIN_DATA
+        0 10.0 20.0 30.0
+        # inline comment
+        1 20.0 30.0 40.0
+        END_DATA
+        # another comment
+        NUMBER_OF_FIELDS 3
+        BEGIN_DATA_FORMAT
+        VERTEX_0 VERTEX_1 VERTEX_2
+        END_DATA_FORMAT
+        NUMBER_OF_SETS 1
+        BEGIN_DATA
+        0 1 0
+        END_DATA
+        """
+
+        let mesh = try GamutMeshParser.parse(text: text)
+        #expect(mesh.vertices.count == 2)
+        #expect(mesh.faces.count == 1)
+    }
+
+    @Test("Remaps coordinates to x=a*, y=L*, z=b*")
+    func remapsCoordinates() throws {
+        let text = """
+        NUMBER_OF_FIELDS 4
+        BEGIN_DATA_FORMAT
+        VERTEX_NO LAB_L LAB_A LAB_B
+        END_DATA_FORMAT
+        NUMBER_OF_SETS 1
+        BEGIN_DATA
+        0 50.0 -20.0 80.0
+        END_DATA
+        """
+
+        let mesh = try GamutMeshParser.parse(text: text)
+        #expect(mesh.vertices.first?.position == SIMD3<Float>(-20, 50, 80))
+    }
+
+    @Test("Computes per-vertex sRGB colour")
+    func computesVertexColor() throws {
+        let text = """
+        NUMBER_OF_FIELDS 4
+        BEGIN_DATA_FORMAT
+        VERTEX_NO LAB_L LAB_A LAB_B
+        END_DATA_FORMAT
+        NUMBER_OF_SETS 1
+        BEGIN_DATA
+        0 100.0 0.0 0.0
+        END_DATA
+        """
+
+        let mesh = try GamutMeshParser.parse(text: text)
+        let white = try #require(mesh.vertices.first).rgb
+        #expect(white.r > 0.95)
+        #expect(white.g > 0.95)
+        #expect(white.b > 0.95)
+    }
+
+    @Test("Drops out-of-bounds face indices")
+    func dropsOutOfBoundsFaces() throws {
+        let text = """
+        NUMBER_OF_FIELDS 4
+        BEGIN_DATA_FORMAT
+        VERTEX_NO LAB_L LAB_A LAB_B
+        END_DATA_FORMAT
+        NUMBER_OF_SETS 2
+        BEGIN_DATA
+        0 10.0 0.0 0.0
+        1 20.0 0.0 0.0
+        END_DATA
+        NUMBER_OF_FIELDS 3
+        BEGIN_DATA_FORMAT
+        VERTEX_0 VERTEX_1 VERTEX_2
+        END_DATA_FORMAT
+        NUMBER_OF_SETS 2
+        BEGIN_DATA
+        0 1 0
+        0 1 99
+        END_DATA
+        """
+
+        let mesh = try GamutMeshParser.parse(text: text)
+        #expect(mesh.faces.count == 1)
+    }
+
+    @Test("Throws on empty file")
+    func throwsOnEmptyFile() {
+        #expect(throws: GamutMeshParseError.noDataBlock) {
+            _ = try GamutMeshParser.parse(text: "")
+        }
+    }
+
+    @Test("Throws when file is missing")
+    func throwsWhenMissing() {
+        let url = URL(fileURLWithPath: "/nonexistent/path/to/mesh.gam")
+        #expect(throws: GamutMeshParseError.missingFile) {
+            _ = try GamutMeshParser.parse(url: url)
+        }
+    }
+}

Tests/ICCeryUITests/Fixtures/bin/iccgamut

@@ -1,5 +1,5 @@
 #!/bin/sh
-# Mock iccgamut for Milestone 5 UI tests.
+# Mock iccgamut for Milestone 5/6 UI tests.
 # Writes {stem}.gam next to the profile path.
 last=""
 for arg in "$@"; do last="$arg"; done
@@ -9,5 +9,9 @@ if [ "${ICCERY_MOCK_ICCGAMUT_EXIT:-0}" -ne 0 ]; then
 fi
 stem=$(basename "$last" | sed 's/\.icc$//; s/\.icm$//')
 dir=$(dirname "$last")
-touch "$dir/$stem.gam"
+if [ -n "${ICCERY_MOCK_GAMUT_SOURCE}" ] && [ -f "${ICCERY_MOCK_GAMUT_SOURCE}" ]; then
+  cp "${ICCERY_MOCK_GAMUT_SOURCE}" "$dir/$stem.gam"
+else
+  touch "$dir/$stem.gam"
+fi
 exit 0

Tests/ICCeryUITests/Milestone6GamutUITests.swift

@@ -0,0 +1,118 @@
+import Foundation
+import XCTest
+
+/// Milestone 6 — Issue #28 native SceneKit gamut viewer acceptance tests.
+@MainActor
+final class Milestone6GamutUITests: XCTestCase {
+
+    private var app: XCUIApplication!
+    private var testRoot: URL!
+    private var binDir: URL!
+    private var workDir: URL!
+    private var appDataDir: URL!
+    private var referenceGamutURL: URL!
+
+    override func setUp() async throws {
+        continueAfterFailure = false
+        testRoot = FileManager.default.temporaryDirectory
+            .appendingPathComponent("iccery-ui-m6-gamut-\(UUID().uuidString)")
+        binDir = URL(fileURLWithPath: #filePath)
+            .deletingLastPathComponent()
+            .appendingPathComponent("Fixtures/bin")
+        workDir = testRoot.appendingPathComponent("work")
+        appDataDir = testRoot.appendingPathComponent("AppData")
+
+        // The bundled sRGB reference used by the app; copied into the test workdir
+        // by the mock iccgamut so the profile gamut is a real, parseable mesh.
+        referenceGamutURL = URL(fileURLWithPath: #filePath)
+            .deletingLastPathComponent()
+            .deletingLastPathComponent()
+            .deletingLastPathComponent()
+            .appendingPathComponent("Resources/Argyll/reference_gamuts/sRGB.gam")
+
+        try FileManager.default.createDirectory(
+            at: workDir, withIntermediateDirectories: true)
+        try FileManager.default.createDirectory(
+            at: appDataDir, withIntermediateDirectories: true)
+
+        // Pre-stage a measured .ti3 and start the wizard on Stage 4.
+        FileManager.default.createFile(
+            atPath: workDir.appendingPathComponent("mytarget.ti3").path,
+            contents: Data("MOCK_TI3".utf8),
+            attributes: nil)
+
+        let state: [String: Any] = [
+            "currentStage": 4,
+            "basename": "mytarget",
+            "cwd": workDir.path,
+            "printerName": "MockPrinter",
+            "sessionMode": "profile"
+        ]
+        let stateData = try JSONSerialization.data(withJSONObject: state, options: [])
+        try stateData.write(to: appDataDir.appendingPathComponent("wizard_state.json"))
+
+        app = XCUIApplication()
+        app.launchEnvironment = [
+            "ICCERY_UI_TESTING": "1",
+            "ICCERY_TEST_ROOT": testRoot.path,
+            "ICCERY_ARGYLL_BINARY_DIR": binDir.path,
+            "ICCERY_TEST_WORKDIR": workDir.path,
+            "ICCERY_MOCK_GAMUT_SOURCE": referenceGamutURL.path,
+        ]
+    }
+
+    override func tearDown() async throws {
+        app?.terminate()
+        app = nil
+        if let testRoot {
+            try? FileManager.default.removeItem(at: testRoot)
+        }
+        testRoot = nil
+    }
+
+    private func element(_ id: String) -> XCUIElement {
+        let inApp = app.descendants(matching: .any)[id].firstMatch
+        if inApp.exists { return inApp }
+        return app.sheets.firstMatch.descendants(matching: .any)[id].firstMatch
+    }
+
+    private func waitFor(_ id: String, timeout: TimeInterval = 15) -> XCUIElement {
+        let deadline = Date().addingTimeInterval(timeout)
+        while Date() < deadline {
+            let el = element(id)
+            if el.exists { return el }
+            RunLoop.current.run(until: Date().addingTimeInterval(0.1))
+        }
+        let el = element(id)
+        XCTAssertTrue(el.exists, "Expected element \(id)")
+        return el
+    }
+
+    /// Build and verify the mock profile, then open the native gamut viewer.
+    /// The viewer should load both the reference sRGB mesh and the profile
+    /// gamut copied from that reference.
+    func testViewGamutOpensSceneKitSheet() throws {
+        app.launch()
+        if !app.wait(for: .runningForeground, timeout: 10) {
+            app.activate()
+        }
+
+        waitFor("btnCreateProfile").click()
+
+        waitFor("btnVerifyProfile").click()
+
+        waitFor("btnViewGamut").click()
+
+        let gamutView = waitFor("gamutView")
+        XCTAssertTrue(gamutView.exists)
+
+        let status = waitFor("gamutStatusText")
+        let value = status.value as? String ?? ""
+        XCTAssertTrue(value.contains("faces"), "Gamut status should report mesh faces, got: \(value)")
+
+        // The reset button demonstrates that the viewer is interactive.
+        let reset = waitFor("btnResetGamutCamera")
+        XCTAssertTrue(reset.isEnabled)
+        reset.click()
+    }
+}

project.yml

@@ -25,6 +25,7 @@ targets:
     dependencies:
       - package: ICCeryCore
         product: ICCeryCore
+      - sdk: SceneKit.framework
     postBuildScripts:
       - name: Copy Argyll sidecars
         script: |