diff --git a/apps/ios/Sources/Model/NodeAppModel.swift b/apps/ios/Sources/Model/NodeAppModel.swift
index d15946c1b..5f1cf6d26 100644
--- a/apps/ios/Sources/Model/NodeAppModel.swift
+++ b/apps/ios/Sources/Model/NodeAppModel.swift
@@ -102,14 +102,12 @@ final class NodeAppModel {
         let contextJSON = ClawdisCanvasA2UIAction.compactJSON(userAction["context"])
         let sessionKey = "main"
 
-        let message = ClawdisCanvasA2UIAction.formatAgentMessage(
+        let messageContext = ClawdisCanvasA2UIAction.AgentMessageContext(
             actionName: name,
-            sessionKey: sessionKey,
-            surfaceId: surfaceId,
-            sourceComponentId: sourceComponentId,
-            host: host,
-            instanceId: instanceId,
+            session: .init(key: sessionKey, surfaceId: surfaceId),
+            component: .init(id: sourceComponentId, host: host, instanceId: instanceId),
             contextJSON: contextJSON)
+        let message = ClawdisCanvasA2UIAction.formatAgentMessage(messageContext)
 
         let ok: Bool
         var errorText: String?
diff --git a/apps/macos/Sources/Clawdis/CanvasWindow.swift b/apps/macos/Sources/Clawdis/CanvasWindow.swift
index eaa3b551b..d0fb3d344 100644
--- a/apps/macos/Sources/Clawdis/CanvasWindow.swift
+++ b/apps/macos/Sources/Clawdis/CanvasWindow.swift
@@ -654,14 +654,12 @@ private final class CanvasA2UIActionMessageHandler: NSObject, WKScriptMessageHan
         let contextJSON = ClawdisCanvasA2UIAction.compactJSON(userAction["context"])
 
         // Token-efficient and unambiguous. The agent should treat this as a UI event and (by default) update Canvas.
-        let text = ClawdisCanvasA2UIAction.formatAgentMessage(
+        let messageContext = ClawdisCanvasA2UIAction.AgentMessageContext(
             actionName: name,
-            sessionKey: self.sessionKey,
-            surfaceId: surfaceId,
-            sourceComponentId: sourceComponentId,
-            host: InstanceIdentity.displayName,
-            instanceId: instanceId,
+            session: .init(key: self.sessionKey, surfaceId: surfaceId),
+            component: .init(id: sourceComponentId, host: InstanceIdentity.displayName, instanceId: instanceId),
             contextJSON: contextJSON)
+        let text = ClawdisCanvasA2UIAction.formatAgentMessage(messageContext)
 
         Task { [weak webView] in
             if AppStateStore.shared.connectionMode == .local {
diff --git a/apps/shared/ClawdisKit/Sources/ClawdisKit/CanvasA2UIAction.swift b/apps/shared/ClawdisKit/Sources/ClawdisKit/CanvasA2UIAction.swift
index dc7a8fdaa..0acd06773 100644
--- a/apps/shared/ClawdisKit/Sources/ClawdisKit/CanvasA2UIAction.swift
+++ b/apps/shared/ClawdisKit/Sources/ClawdisKit/CanvasA2UIAction.swift
@@ -1,6 +1,42 @@
 import Foundation
 
 public enum ClawdisCanvasA2UIAction: Sendable {
+    public struct AgentMessageContext: Sendable {
+        public struct Session: Sendable {
+            public var key: String
+            public var surfaceId: String
+
+            public init(key: String, surfaceId: String) {
+                self.key = key
+                self.surfaceId = surfaceId
+            }
+        }
+
+        public struct Component: Sendable {
+            public var id: String
+            public var host: String
+            public var instanceId: String
+
+            public init(id: String, host: String, instanceId: String) {
+                self.id = id
+                self.host = host
+                self.instanceId = instanceId
+            }
+        }
+
+        public var actionName: String
+        public var session: Session
+        public var component: Component
+        public var contextJSON: String?
+
+        public init(actionName: String, session: Session, component: Component, contextJSON: String?) {
+            self.actionName = actionName
+            self.session = session
+            self.component = component
+            self.contextJSON = contextJSON
+        }
+    }
+
     public static func extractActionName(_ userAction: [String: Any]) -> String? {
         let keys = ["name", "action"]
         for key in keys {
@@ -30,25 +66,16 @@ public enum ClawdisCanvasA2UIAction: Sendable {
         return str
     }
 
-    public static func formatAgentMessage(
-        actionName: String,
-        sessionKey: String,
-        surfaceId: String,
-        sourceComponentId: String,
-        host: String,
-        instanceId: String,
-        contextJSON: String?)
-        -> String
-    {
-        let ctxSuffix = contextJSON.flatMap { $0.isEmpty ? nil : " ctx=\($0)" } ?? ""
+    public static func formatAgentMessage(_ context: AgentMessageContext) -> String {
+        let ctxSuffix = context.contextJSON.flatMap { $0.isEmpty ? nil : " ctx=\($0)" } ?? ""
         return [
             "CANVAS_A2UI",
-            "action=\(self.sanitizeTagValue(actionName))",
-            "session=\(self.sanitizeTagValue(sessionKey))",
-            "surface=\(self.sanitizeTagValue(surfaceId))",
-            "component=\(self.sanitizeTagValue(sourceComponentId))",
-            "host=\(self.sanitizeTagValue(host))",
-            "instance=\(self.sanitizeTagValue(instanceId))\(ctxSuffix)",
+            "action=\(self.sanitizeTagValue(context.actionName))",
+            "session=\(self.sanitizeTagValue(context.session.key))",
+            "surface=\(self.sanitizeTagValue(context.session.surfaceId))",
+            "component=\(self.sanitizeTagValue(context.component.id))",
+            "host=\(self.sanitizeTagValue(context.component.host))",
+            "instance=\(self.sanitizeTagValue(context.component.instanceId))\(ctxSuffix)",
             "default=update_canvas",
         ].joined(separator: " ")
     }
diff --git a/apps/shared/ClawdisKit/Sources/ClawdisKit/CanvasA2UIJSONL.swift b/apps/shared/ClawdisKit/Sources/ClawdisKit/CanvasA2UIJSONL.swift
index 53ae33e62..0e8d3b4f5 100644
--- a/apps/shared/ClawdisKit/Sources/ClawdisKit/CanvasA2UIJSONL.swift
+++ b/apps/shared/ClawdisKit/Sources/ClawdisKit/CanvasA2UIJSONL.swift
@@ -27,7 +27,12 @@ public enum ClawdisCanvasA2UIJSONL: Sendable {
     }
 
     public static func validateV0_8(_ items: [ParsedItem]) throws {
-        let allowed = Set(["beginRendering", "surfaceUpdate", "dataModelUpdate", "deleteSurface"])
+        let allowed = Set([
+            "beginRendering",
+            "surfaceUpdate",
+            "dataModelUpdate",
+            "deleteSurface",
+        ])
         for item in items {
             guard let dict = item.message.value as? [String: AnyCodable] else {
                 throw NSError(domain: "A2UI", code: 1, userInfo: [
@@ -39,7 +44,8 @@ public enum ClawdisCanvasA2UIJSONL: Sendable {
                 throw NSError(domain: "A2UI", code: 2, userInfo: [
                     NSLocalizedDescriptionKey: """
                     A2UI JSONL line \(item.lineNumber): looks like A2UI v0.9 (`createSurface`).
-                    Canvas currently supports A2UI v0.8 server→client messages (`beginRendering`, `surfaceUpdate`, `dataModelUpdate`, `deleteSurface`).
+                    Canvas currently supports A2UI v0.8 server→client messages
+                    (`beginRendering`, `surfaceUpdate`, `dataModelUpdate`, `deleteSurface`).
                     """,
                 ])
             }
diff --git a/apps/shared/ClawdisKit/Tests/ClawdisKitTests/CanvasA2UIActionTests.swift b/apps/shared/ClawdisKit/Tests/ClawdisKitTests/CanvasA2UIActionTests.swift
index 480dd4863..f2b2aa676 100644
--- a/apps/shared/ClawdisKit/Tests/ClawdisKitTests/CanvasA2UIActionTests.swift
+++ b/apps/shared/ClawdisKit/Tests/ClawdisKitTests/CanvasA2UIActionTests.swift
@@ -17,14 +17,12 @@ import Testing
     }
 
     @Test func formatAgentMessageIsTokenEfficientAndUnambiguous() {
-        let msg = ClawdisCanvasA2UIAction.formatAgentMessage(
+        let messageContext = ClawdisCanvasA2UIAction.AgentMessageContext(
             actionName: "Get Weather",
-            sessionKey: "main",
-            surfaceId: "main",
-            sourceComponentId: "btnWeather",
-            host: "Peter’s iPad",
-            instanceId: "ipad16,6",
+            session: .init(key: "main", surfaceId: "main"),
+            component: .init(id: "btnWeather", host: "Peter’s iPad", instanceId: "ipad16,6"),
             contextJSON: "{\"city\":\"Vienna\"}")
+        let msg = ClawdisCanvasA2UIAction.formatAgentMessage(messageContext)
 
         #expect(msg.contains("CANVAS_A2UI "))
         #expect(msg.contains("action=Get_Weather"))