fix: enable image attachments in chat messages for Claude API

Images were previously converted to markdown data URLs which Claude API
treats as plain text, not as actual images.

Changes:
- Add parseMessageWithAttachments() that returns {message, images[]}
- Pass images through the stack to session.prompt() as content blocks
- Filter null/empty attachments before parsing
- Strip data URL prefix if client sends it

This enables iOS and other clients to send images that Claude can actually see.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/gateway/server-methods/chat.ts

@@ -13,7 +13,10 @@ import {
   isChatStopCommandText,
   resolveChatRunExpiresAtMs,
 } from "../chat-abort.js";
-import { buildMessageWithAttachments } from "../chat-attachments.js";
+import {
+  type ChatImageContent,
+  parseMessageWithAttachments,
+} from "../chat-attachments.js";
 import {
   ErrorCodes,
   errorShape,
@@ -181,29 +184,34 @@ export const chatHandlers: GatewayRequestHandlers = {
     };
     const stopCommand = isChatStopCommandText(p.message);
     const normalizedAttachments =
-      p.attachments?.map((a) => ({
-        type: typeof a?.type === "string" ? a.type : undefined,
-        mimeType: typeof a?.mimeType === "string" ? a.mimeType : undefined,
-        fileName: typeof a?.fileName === "string" ? a.fileName : undefined,
-        content:
-          typeof a?.content === "string"
-            ? a.content
-            : ArrayBuffer.isView(a?.content)
-              ? Buffer.from(
-                  a.content.buffer,
-                  a.content.byteOffset,
-                  a.content.byteLength,
-                ).toString("base64")
-              : undefined,
-      })) ?? [];
-    let messageWithAttachments = p.message;
+      p.attachments
+        ?.map((a) => ({
+          type: typeof a?.type === "string" ? a.type : undefined,
+          mimeType: typeof a?.mimeType === "string" ? a.mimeType : undefined,
+          fileName: typeof a?.fileName === "string" ? a.fileName : undefined,
+          content:
+            typeof a?.content === "string"
+              ? a.content
+              : ArrayBuffer.isView(a?.content)
+                ? Buffer.from(
+                    a.content.buffer,
+                    a.content.byteOffset,
+                    a.content.byteLength,
+                  ).toString("base64")
+                : undefined,
+        }))
+        .filter((a) => a.content && a.mimeType) ?? [];
+    let parsedMessage = p.message;
+    let parsedImages: ChatImageContent[] = [];
     if (normalizedAttachments.length > 0) {
       try {
-        messageWithAttachments = buildMessageWithAttachments(
+        const parsed = parseMessageWithAttachments(
           p.message,
           normalizedAttachments,
           { maxBytes: 5_000_000 },
         );
+        parsedMessage = parsed.message;
+        parsedImages = parsed.images;
       } catch (err) {
         respond(
           false,
@@ -312,7 +320,8 @@ export const chatHandlers: GatewayRequestHandlers = {
 
       void agentCommand(
         {
-          message: messageWithAttachments,
+          message: parsedMessage,
+          images: parsedImages.length > 0 ? parsedImages : undefined,
           sessionId,
           sessionKey: p.sessionKey,
           runId: clientRunId,