carry attached images through to the model

The composer already uploaded an image, split its data URL and put the bytes on the wire as
`images`. Nothing on the server read them. The `chat` ClientMessage had no such field, and the
prompt reached the sidecar as a bare string, so all the model ever saw was the client-generated
`[Attached image: …]` placeholder — a label describing a picture it was never shown.

The transport was never the obstacle: `query()` consumes an async iterable of user messages whose
`content` is an Anthropic `MessageParam`, and only `pushTurn` hardcoding a string kept it to text.
So `images` is threaded through the four hops that dropped it and turned into native image content
blocks at the end, renaming `mediaType` to the API's `media_type` at that last step.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/api/chat/types.ts

@@ -45,6 +45,15 @@ export type GroupMeta = {
 
 export type ThinkingLevel = 'off' | 'minimal' | 'low' | 'medium' | 'high' | 'xhigh';
 
+/**
+ * An image pasted or attached in the composer, already split out of its data URL by the client.
+ *
+ * `/upload` also writes the file to disk, but the on-disk copy is for the attachment list and history —
+ * what the model actually reads is these bytes, carried through to a native image content block. Naming
+ * is camelCase on the wire and renamed to the Anthropic `media_type` at the last step.
+ */
+export type PromptImage = { mediaType: string; data: string };
+
 export type ClientMessage =
   | {
       type: 'chat';
@@ -56,6 +65,7 @@ export type ClientMessage =
       cwdRoot?: string;
       groupSlug?: string;
       attachmentIds?: string[];
+      images?: PromptImage[];
       thinking?: ThinkingLevel;
       context?: string;
       contextId?: string;

src/servers/api/chat/websocket.ts

@@ -1,6 +1,6 @@
 import type { ServerWebSocket } from 'bun';
 import { randomUUID } from 'crypto';
-import type { ClientMessage, ServerMessage, Message, TurnMessage, UserSession } from './types';
+import type { ClientMessage, ServerMessage, Message, PromptImage, TurnMessage, UserSession } from './types';
 import { sessionManager } from './session-manager';
 import { sendClaudeCodeStreaming } from '@@/channels/send-claude-code';
 import { sendOpenCodeStreaming } from '@@/channels/send-opencode';
@@ -248,6 +248,7 @@ async function handleChat(
     cwdRoot?: string;
     groupSlug?: string;
     attachmentIds?: string[];
+    images?: PromptImage[];
     thinking?: string;
     context?: string;
     contextId?: string;
@@ -286,6 +287,7 @@ async function handleClaudeCodeChat(
     contextId?: string;
     cwd?: string;
     cwdRoot?: string;
+    images?: PromptImage[];
     resumeSessionId?: string;
   },
   effectivePrompt: string,
@@ -338,6 +340,7 @@ async function handleClaudeCodeChat(
         email,
         username,
         prompt: effectivePrompt,
+        images: msg.images,
         sessionKey: sessionId,
         cwd,
         model,
@@ -353,6 +356,7 @@ async function handleClaudeCodeChat(
         email,
         username,
         prompt: effectivePrompt,
+        images: msg.images,
         sessionKey: sessionId,
         cwd,
         model,