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/sidecar/claude/claude-manager.ts

@@ -2,7 +2,7 @@ import { existsSync } from 'node:fs';
 import { homedir } from 'node:os';
 import { join } from 'node:path';
 import { query, type Query } from '@anthropic-ai/claude-agent-sdk';
-import type { ChatEvent } from '../../api/chat/types';
+import type { ChatEvent, PromptImage } from '../../api/chat/types';
 import type { ClaudeSpawnParams, ClaudeSpawnStreamingParams, ClaudeCodeResult } from '../protocol';
 import { setClaudeSession, clearClaudeSession, getClaudeSession } from './state';
 import { createParseState, processMessage } from './stream-parser';
@@ -147,9 +147,18 @@ export async function spawnClaude(params: ClaudeSpawnParams): Promise<ClaudeCode
 // ChatEvent and forwards it. Idle policy: torn down after IDLE_TIMEOUT_MS with no new turn, or on an
 // explicit kill (user "disconnect"). "Stop" is interrupt() — it ends the turn but keeps the session.
 
+/**
+ * `content` is an Anthropic `MessageParam` content: a bare string, or the block array we build when the
+ * turn carries images. Blocks are what make an attached screenshot actually reach the model — the string
+ * form can only carry the client's `[Attached image: …]` placeholder, which is a label, not the picture.
+ */
+type ContentBlock =
+  | { type: 'text'; text: string }
+  | { type: 'image'; source: { type: 'base64'; media_type: string; data: string } };
+
 type SdkUserMessage = {
   type: 'user';
-  message: { role: 'user'; content: string };
+  message: { role: 'user'; content: string | ContentBlock[] };
   parent_tool_use_id: null;
   session_id: string;
 };
@@ -157,7 +166,7 @@ type SdkUserMessage = {
 type PersistentSession = {
   sessionKey: string;
   query: Query;
-  pushTurn: (prompt: string) => void;
+  pushTurn: (prompt: string, images?: PromptImage[]) => void;
   closeInput: () => void;
   abort: AbortController;
   emit: (event: ChatEvent) => void;
@@ -264,12 +273,24 @@ function createSession(params: ClaudeSpawnStreamingParams, onEvent: (event: Chat
   });
 
   session.query = q;
-  session.pushTurn = (prompt: string) => {
+  session.pushTurn = (prompt: string, images?: PromptImage[]) => {
     if (session.idleTimer) clearTimeout(session.idleTimer);
     session.isGenerating = true;
+    // Images first, then the text: the model reads what it is looking at before what to do about it.
+    const content: string | ContentBlock[] = images?.length
+      ? [
+          ...images.map(
+            (img): ContentBlock => ({
+              type: 'image',
+              source: { type: 'base64', media_type: img.mediaType, data: img.data },
+            }),
+          ),
+          { type: 'text', text: prompt },
+        ]
+      : prompt;
     input.push({
       type: 'user',
-      message: { role: 'user', content: prompt },
+      message: { role: 'user', content },
       parent_tool_use_id: null,
       session_id: sessionKey,
     });
@@ -333,7 +354,7 @@ export async function spawnClaudeStreaming(
   } else {
     session = createSession(params, onEvent);
   }
-  session.pushTurn(params.prompt);
+  session.pushTurn(params.prompt, params.images);
 }
 
 /** Interrupt the current turn but KEEP the session alive (the "stop" button). */

src/servers/sidecar/protocol.ts

@@ -1,4 +1,4 @@
-import type { MessageCost, TurnMessage } from '../api/chat/types';
+import type { MessageCost, PromptImage, TurnMessage } from '../api/chat/types';
 
 // ── Envelope ──
 
@@ -121,6 +121,7 @@ export type ClaudeSpawnStreamingParams = {
   email: string;
   username: string;
   prompt: string;
+  images?: PromptImage[]; // sent as native image content blocks alongside the prompt text
   sessionKey: string;
   cwd?: string;
   model?: string;