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, 15 insertions, 0 deletions

diff --git a/src/features/chat/model-select.ts b/src/features/chat/model-select.ts
index db41772..602e0ef 100644
--- a/src/features/chat/model-select.ts
+++ b/src/features/chat/model-select.ts
@@ -1,3 +1,5 @@
+import type { ModelMetadata } from "@dispatch/transport-contract";
+
 /**
  * Pure helpers for the two-step model picker.
  *
@@ -47,3 +49,16 @@ export function modelsForKey(models: readonly string[], key: string): string[] {
   }
   return out;
 }
+
+/**
+ * Whether a given full model name (`<key>/<model>`) is vision-capable — i.e.
+ * `GET /models` `modelInfo[name].vision === true`. Absent/`false`/unknown →
+ * `false` (the server's vision handoff transcribes images to text for it).
+ * Pure lookup against the catalog metadata; zero DOM.
+ */
+export function isVisionModel(
+  modelInfo: Readonly<Record<string, ModelMetadata>>,
+  fullName: string,
+): boolean {
+  return modelInfo[fullName]?.vision === true;
+}