send images to opencode, which never needed the fork

B4 properly. The composer gate was the honest stopgap; this is the fix. opencode run takes
attachments with --file, so images work on the subprocess path we already use — the parity
doc had them down as phase 4, behind the serve migration, and they were not.

The bug was one omission: handleOpenCodeChat`s msg type had no images field, so the browser
sent them, the bubble rendered them, and they stopped at that signature. Nothing reported a
loss anywhere.

Attachments are paths, not inline data, so the sidecar spills each image to a temp file for
the length of the turn and removes it in settle — the same place every other per-turn
resource is released, so a killed or superseded turn cleans up too.

The load-bearing detail is `--` before the prompt: --file is an array option, so without the
separator the prompt is eaten as another filename and the turn dies with "File not found:"
followed by the entire message. Confirmed against the binary, and pinned by a test that
records argv from a stub.

list-models now reports each model own capability instead of a hardcoded false — opencode
publishes capabilities.input.image per model and nothing had ever read it. Defaults to false,
so a model that does not declare it keeps the affordance hidden.

Verified end to end: a red png sent over the chat socket to opencode/claude-sonnet-4-6 came
back "Red".

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

src/servers/api/chat/websocket.ts

@@ -396,6 +396,10 @@ async function handleOpenCodeChat(
     cwd?: string;
     cwdRoot?: string;
     resumeSessionId?: string;
+    // The whole of B4 lived in this omission. The browser sent images, the bubble rendered them, and
+    // they stopped at this signature — so they were never passed on and never reached the model, with
+    // nothing anywhere reporting a loss.
+    images?: PromptImage[];
   },
   effectivePrompt: string,
 ): Promise<void> {
@@ -457,6 +461,7 @@ async function handleOpenCodeChat(
       cwd,
       model,
       resumeSessionId: msg.resumeSessionId,
+      images: msg.images,
       onMessage,
     });