Generate typed Go union interfaces (#1252)

* Generate typed Go union interfaces

* Update Go image input docs for attachment variants

* Preserve unknown permission decision kind

* Simplify Go union codegen cleanup

* Fix Go scenario typed union examples

* Fix Go matcher codegen lint

* Generate Go interfaces for shape-distinct unions

* Refactor Go union codegen planning

* Fix raw session event JSON fallback

* Generate Go unions from required fields

* regenerate

Author: qmuntal

docs/features/image-input.md

@@ -120,9 +120,9 @@ func main() {
 	session.Send(ctx, copilot.MessageOptions{
 		Prompt: "Describe what you see in this image",
 		Attachments: []copilot.Attachment{
-			{
-				Type: copilot.AttachmentTypeFile,
-				Path: &path,
+            &copilot.UserMessageAttachmentFile{
+                DisplayName: "screenshot.png",
+                Path:        path,
 			},
 		},
 	})
@@ -146,9 +146,9 @@ path := "/absolute/path/to/screenshot.png"
 session.Send(ctx, copilot.MessageOptions{
     Prompt: "Describe what you see in this image",
     Attachments: []copilot.Attachment{
-        {
-            Type: copilot.AttachmentTypeFile,
-            Path: &path,
+        &copilot.UserMessageAttachmentFile{
+            DisplayName: "screenshot.png",
+            Path:        path,
         },
     },
 })
@@ -343,10 +343,9 @@ func main() {
 	session.Send(ctx, copilot.MessageOptions{
 		Prompt: "Describe what you see in this image",
 		Attachments: []copilot.Attachment{
-			{
-				Type:        copilot.AttachmentTypeBlob,
-				Data:        &base64ImageData,
-				MIMEType:    &mimeType,
+            &copilot.UserMessageAttachmentBlob{
+                Data:        base64ImageData,
+                MIMEType:    mimeType,
 				DisplayName: &displayName,
 			},
 		},
@@ -361,10 +360,9 @@ displayName := "screenshot.png"
 session.Send(ctx, copilot.MessageOptions{
     Prompt: "Describe what you see in this image",
     Attachments: []copilot.Attachment{
-        {
-            Type:        copilot.AttachmentTypeBlob,
-            Data:        &base64ImageData, // base64-encoded string
-            MIMEType:    &mimeType,
+        &copilot.UserMessageAttachmentBlob{
+            Data:        base64ImageData, // base64-encoded string
+            MIMEType:    mimeType,
             DisplayName: &displayName,
         },
     },

go/README.md

@@ -246,9 +246,9 @@ The SDK supports image attachments via the `Attachments` field in `MessageOption
 _, err = session.Send(context.Background(), copilot.MessageOptions{
     Prompt: "What's in this image?",
     Attachments: []copilot.Attachment{
-        {
-            Type: "file",
-            Path: "/path/to/image.jpg",
+        &copilot.UserMessageAttachmentFile{
+            DisplayName: "image.jpg",
+            Path:        "/path/to/image.jpg",
         },
     },
 })
@@ -258,10 +258,9 @@ mimeType := "image/png"
 _, err = session.Send(context.Background(), copilot.MessageOptions{
     Prompt: "What's in this image?",
     Attachments: []copilot.Attachment{
-        {
-            Type:     copilot.AttachmentTypeBlob,
-            Data:     &base64ImageData,
-            MIMEType: &mimeType,
+        &copilot.UserMessageAttachmentBlob{
+            Data:     base64ImageData,
+            MIMEType: mimeType,
         },
     },
 })