feat(vision): image paste + transcript image rendering + vision badge

Vision & vision-handoff frontend (consumes the backend's additive
[email protected] / [email protected] image types — no version bump).

Contracts mirrored:
- .dispatch/wire.reference.md: ImageChunk added to the Chunk union +
  ImageChunk/ImageInput interfaces.
- .dispatch/transport-contract.reference.md: ChatRequest.images,
  ModelMetadata.vision, + ImageChunk/ImageInput re-exports.

Core (core/chunks):
- conformance: assertChunkExhaustive handles the new 'image' variant
  (the guard caught it — its purpose).
- appendUserMessage(state, text, images?) echoes a [text, image, ...]
  user run; the user-message event dedup scans the trailing user run
  (not just the last chunk) so an image-bearing echo doesn't duplicate
  the text; applyHistory's during-gen dedup matches a multi-chunk echo
  by content equality (chunkContentEquals + trailingRun helpers).

UI:
- ChatView renders user 'image' chunks as lazy <img> bubbles; a
  non-vision model's persisted [image, analysis-text] both render.
  read_image tool renders generically (no special-casing).
- Composer: clipboard paste / file picker / drag-drop of images ->
  base64 data URLs, thumbnail previews with remove, forwarded on
  chat.send (omitted when none). Image-only sends allowed; steering
  (chat.queue) never forwards images.
- ModelSelector: vision badge (isVisionModel) marks vision-capable
  models; indicator shows native-vision vs vision-handoff hint.

Store wiring: ChatStore.send + AppStore.send + App.svelte handleSend
thread images through; chat.send still omits cwd (only images added).

Verification: svelte-check 0/0; vitest 901/901 (run twice, +34 new);
biome clean; vite build OK. See backend-handoff.md §2j.

Not merged or pushed.

1 files changed, 28 insertions, 0 deletions

diff --git a/src/app/store.test.ts b/src/app/store.test.ts
index 947a9b0..7130c4d 100644
--- a/src/app/store.test.ts
+++ b/src/app/store.test.ts
@@ -423,6 +423,34 @@ describe("createAppStore", () => {
     store.dispose();
   });
 
+  it("sending from draft forwards staged images on chat.send", () => {
+    const ws = fakeSocket();
+    const store = createAppStore({
+      socketFactory: () => ws,
+      fetchImpl: fakeFetchImpl(),
+      localStorage: createFakeStorage(),
+    });
+    ws.resolveOpen();
+    ws.sent.length = 0;
+
+    const images = [
+      { url: "data:image/png;base64,AAAA", mimeType: "image/png" },
+      { url: "https://example.com/x.jpg" },
+    ];
+    store.send("describe these", images);
+
+    const msgs = parseSent(ws);
+    const chatSend = msgs.find((m) => (m as { type: string }).type === "chat.send") as
+      | { type: string; message: string; images?: { url: string }[] }
+      | undefined;
+    expect(chatSend).toBeTruthy();
+    expect(chatSend?.images).toEqual(images);
+    // The optimistic echo includes the image chunks.
+    expect(store.activeChat.chunks.some((c) => c.chunk.type === "image")).toBe(true);
+
+    store.dispose();
+  });
+
   it("an incoming chat.delta renders in the transcript", () => {
     const ws = fakeSocket();
     const store = createAppStore({