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, 88 insertions, 1 deletions

diff --git a/src/features/chat/store.test.ts b/src/features/chat/store.test.ts
index c052d1b..8f36994 100644
--- a/src/features/chat/store.test.ts
+++ b/src/features/chat/store.test.ts
@@ -1,4 +1,4 @@
-import type { AgentEvent, StepId, StoredChunk } from "@dispatch/wire";
+import type { AgentEvent, ImageInput, StepId, StoredChunk } from "@dispatch/wire";
 import { describe, expect, it, vi } from "vitest";
 import { createChatStore } from "./store.svelte";
 import {
@@ -144,6 +144,93 @@ describe("createChatStore", () => {
     store.dispose();
   });
 
+  it("send forwards staged images on chat.send and echoes them provisionally", () => {
+    const transport = createFakeTransport();
+    const historySync = createFakeHistorySync();
+    const metricsSync = createFakeMetricsSync();
+    const cache = createFakeCache();
+    const store = createChatStore({
+      conversationId: CONV_ID,
+      transport: transport.impl,
+      historySync: historySync.impl,
+      metricsSync: metricsSync.impl,
+      cache: cache.impl,
+    });
+
+    const images: ImageInput[] = [
+      { url: "data:image/png;base64,AAAA", mimeType: "image/png" },
+      { url: "https://example.com/cat.jpg" },
+    ];
+    store.send("look at this", images);
+
+    expect(transport.sent).toHaveLength(1);
+    const msg = transport.sent[0];
+    expect(msg?.type).toBe("chat.send");
+    expect(msg?.message).toBe("look at this");
+    expect(msg?.images).toEqual(images);
+
+    // Optimistic echo: a text chunk + two image chunks, provisional.
+    const chunks = store.chunks;
+    expect(chunks).toHaveLength(3);
+    expect(chunks[0]?.chunk).toEqual({ type: "text", text: "look at this" });
+    expect(chunks[1]?.chunk).toEqual({ type: "image", url: images[0]?.url, mimeType: "image/png" });
+    expect(chunks[2]?.chunk).toEqual({ type: "image", url: images[1]?.url });
+
+    store.dispose();
+  });
+
+  it("send omits images on the wire when none are staged (backward compatible)", () => {
+    const transport = createFakeTransport();
+    const store = createChatStore({
+      conversationId: CONV_ID,
+      transport: transport.impl,
+      historySync: createFakeHistorySync().impl,
+      metricsSync: createFakeMetricsSync().impl,
+      cache: createFakeCache().impl,
+    });
+
+    store.send("just text");
+
+    expect(transport.sent[0]).not.toHaveProperty("images");
+    store.dispose();
+  });
+
+  it("send omits images on the wire for an empty array", () => {
+    const transport = createFakeTransport();
+    const store = createChatStore({
+      conversationId: CONV_ID,
+      transport: transport.impl,
+      historySync: createFakeHistorySync().impl,
+      metricsSync: createFakeMetricsSync().impl,
+      cache: createFakeCache().impl,
+    });
+
+    store.send("just text", []);
+
+    expect(transport.sent[0]).not.toHaveProperty("images");
+    store.dispose();
+  });
+
+  it("send allows an images-only message (empty text)", () => {
+    const transport = createFakeTransport();
+    const store = createChatStore({
+      conversationId: CONV_ID,
+      transport: transport.impl,
+      historySync: createFakeHistorySync().impl,
+      metricsSync: createFakeMetricsSync().impl,
+      cache: createFakeCache().impl,
+    });
+
+    store.send("", [{ url: "data:image/png;base64,AAAA", mimeType: "image/png" }]);
+
+    expect(transport.sent[0]?.message).toBe("");
+    expect(transport.sent[0]?.images).toHaveLength(1);
+    // The echo is image-only (no text chunk).
+    expect(store.chunks).toHaveLength(1);
+    expect(store.chunks[0]?.chunk.type).toBe("image");
+    store.dispose();
+  });
+
   describe("queueMessage (chat.queue — steering)", () => {
     it("posts a chat.queue with conversationId + text", () => {
       const transport = createFakeTransport();