iOS: support jpeg canvas snapshots

apps/ios/Sources/Model/NodeAppModel.swift

@@ -403,9 +403,24 @@ final class NodeAppModel {
 
             case ClawdisCanvasCommand.snapshot.rawValue:
                 let params = try? Self.decodeParams(ClawdisCanvasSnapshotParams.self, from: req.paramsJSON)
-                let maxWidth = params?.maxWidth.map { CGFloat($0) }
+                let format = params?.format ?? .jpeg
-                let base64 = try await self.screen.snapshotPNGBase64(maxWidth: maxWidth)
+                let maxWidth: CGFloat? = {
-                let payload = try Self.encodePayload(["format": "png", "base64": base64])
+                    if let raw = params?.maxWidth, raw > 0 { return CGFloat(raw) }
+                    // Keep default snapshots comfortably below the gateway client's maxPayload.
+                    // For full-res, clients should explicitly request a larger maxWidth.
+                    return switch format {
+                    case .png: 900
+                    case .jpeg: 1600
+                    }
+                }()
+                let base64 = try await self.screen.snapshotBase64(
+                    maxWidth: maxWidth,
+                    format: format,
+                    quality: params?.quality)
+                let payload = try Self.encodePayload([
+                    "format": format == .jpeg ? "jpeg" : "png",
+                    "base64": base64,
+                ])
                 return BridgeInvokeResponse(id: req.id, ok: true, payloadJSON: payload)
 
             case ClawdisCanvasA2UICommand.reset.rawValue:

apps/ios/Sources/Screen/ScreenController.swift

@@ -147,11 +147,54 @@ final class ScreenController {
         return data.base64EncodedString()
     }
 
+    func snapshotBase64(
+        maxWidth: CGFloat? = nil,
+        format: ClawdisCanvasSnapshotFormat,
+        quality: Double? = nil) async throws -> String
+    {
+        let config = WKSnapshotConfiguration()
+        if let maxWidth {
+            config.snapshotWidth = NSNumber(value: Double(maxWidth))
+        }
+        let image: UIImage = try await withCheckedThrowingContinuation { cont in
+            self.webView.takeSnapshot(with: config) { image, error in
+                if let error {
+                    cont.resume(throwing: error)
+                    return
+                }
+                guard let image else {
+                    cont.resume(throwing: NSError(domain: "Screen", code: 2, userInfo: [
+                        NSLocalizedDescriptionKey: "snapshot failed",
+                    ]))
+                    return
+                }
+                cont.resume(returning: image)
+            }
+        }
+
+        let data: Data?
+        switch format {
+        case .png:
+            data = image.pngData()
+        case .jpeg:
+            let q = (quality ?? 0.82).clamped(to: 0.1...1.0)
+            data = image.jpegData(compressionQuality: q)
+        }
+        guard let data else {
+            throw NSError(domain: "Screen", code: 1, userInfo: [
+                NSLocalizedDescriptionKey: "snapshot encode failed",
+            ])
+        }
+        return data.base64EncodedString()
+    }
+
     // SwiftPM flattens resource directories; ensure resource filenames are unique.
     private static let canvasScaffoldURL: URL? = ClawdisKitResources.bundle.url(
         forResource: "scaffold",
         withExtension: "html")
-    private static let a2uiIndexURL: URL? = ClawdisKitResources.bundle.url(forResource: "index", withExtension: "html")
+    private static let a2uiIndexURL: URL? = ClawdisKitResources.bundle.url(
+        forResource: "index",
+        withExtension: "html")
 
     fileprivate func isTrustedCanvasUIURL(_ url: URL) -> Bool {
         guard url.isFileURL else { return false }
@@ -170,6 +213,14 @@ final class ScreenController {
     }
 }
 
+extension Double {
+    fileprivate func clamped(to range: ClosedRange<Double>) -> Double {
+        if self < range.lowerBound { return range.lowerBound }
+        if self > range.upperBound { return range.upperBound }
+        return self
+    }
+}
+
 // MARK: - Navigation Delegate
 
 /// Handles navigation policy to intercept clawdis:// deep links from canvas