send images on the serve path too, before anyone switches to it

runOpenCodeTurnOnServe ignored params.images entirely, which is defect B4 rebuilt on the new
path: the image renders in your own bubble and the model never receives it, with nothing
reporting a loss. Fixed before the path is switched on for anyone rather than after.

data: URIs, not file://, and that is measured — the wrong choice is accepted with a 200 and
then dies inside the turn with "Anthropic Messages media must contain valid base64". The
data URI round-trips and the model describes the image.

Strictly better than the subprocess path here: no temp file to spill and nothing to clean up,
because the bytes travel in the request.

Both prompt paths carry them — an ordinary send and a mid-turn injection. Verified end to end
through the chat socket with the serve engine on: a red png came back "**Red**", with deltas
streaming.

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

src/servers/sidecar/opencode/serve-runner.ts

@@ -188,7 +188,10 @@ export async function runOpenCodeTurnOnServe(
     try {
       await serveJson(config, `/api/session/${live.openCodeSessionId}/prompt`, {
         method: 'POST',
-        body: JSON.stringify({ prompt: { text: params.prompt }, delivery: 'steer' }),
+        body: JSON.stringify({
+          prompt: { text: params.prompt, files: promptFiles(params.images) },
+          delivery: 'steer',
+        }),
         cwd,
       });
     } catch (err) {
@@ -255,7 +258,10 @@ export async function runOpenCodeTurnOnServe(
       // `delivery` is stated explicitly because it DEFAULTS to `"steer"`, which injects into a running
       // turn. For an ordinary send that is the wrong default — two quick messages would merge into one
       // turn instead of running in order. `steer` is Phase C's job, wired to the button that means it.
-      body: JSON.stringify({ prompt: { text: params.prompt }, delivery: 'queue' }),
+      body: JSON.stringify({
+        prompt: { text: params.prompt, files: promptFiles(params.images) },
+        delivery: 'queue',
+      }),
       cwd,
     });
   } catch (err) {
@@ -273,6 +279,28 @@ function retire(turn: ServeTurn, event: ChatEvent | null): void {
 
 const errText = (err: unknown): string => (err instanceof Error ? err.message : String(err));
 
+/**
+ * Images as `prompt.files`, which this surface takes by URI.
+ *
+ * **`data:` URIs, not `file://`.** Measured, because the choice is not obvious and the wrong one fails
+ * at the provider rather than at the API: a `file://` attachment is accepted with a 200 and then dies
+ * inside the turn with `Anthropic Messages media must contain valid base64`. A `data:` URI round-trips
+ * and the model describes the image.
+ *
+ * This is strictly better than the subprocess path, which has to spill each image to a temp file for
+ * `--file` and delete it afterwards. Here the bytes go in the request and there is nothing to clean up.
+ *
+ * Silently dropping these is exactly defect B4 — the user sees their image in their own bubble and the
+ * model never receives it — so this exists before the serve path is switched on for anyone, not after.
+ */
+function promptFiles(images: OpenCodeRunParams['images']): { uri: string; name: string }[] | undefined {
+  if (!images?.length) return undefined;
+  return images.map((image, index) => ({
+    uri: `data:${image.mediaType || 'image/png'};base64,${image.data}`,
+    name: `attachment-${index + 1}`,
+  }));
+}
+
 /** The serve analog of `listRunningOpenCodeTurns`. Same shape, so the Live panel needs no changes. */
 export function listRunningServeTurns(): { sessionKey: string }[] {
   return [...bySessionKey.keys()].map((sessionKey) => ({ sessionKey }));