Slice 1: surface system + WS transport + composition root

Pure-core feature libraries assembled at the composition root:
- core/protocol: pure reducer over surface catalog/spec/error messages
- features/surface-host: generic field-kind interpreter (toggle/progress/
  selector/stat/button) + pure plan logic; no surface-id special-casing
- adapters/ws: injected WebSocket client (effects at the edge)
- app: composition root store (Svelte 5 runes over the pure reducer),
  host-relative surface WS URL resolution (resolveWsUrl), root App.svelte

Verified green: svelte-check 0/0, vitest 84 passed, biome clean, vite build ok.

1 files changed, 21 insertions, 0 deletions

diff --git a/src/features/surface-host/ui/Button.svelte b/src/features/surface-host/ui/Button.svelte
new file mode 100644
index 0000000..62d7acf
--- /dev/null
+++ b/src/features/surface-host/ui/Button.svelte
@@ -0,0 +1,21 @@
+<script lang="ts">
+	import type { InvokeMessage } from "@dispatch/ui-contract";
+	import type { ButtonFieldView } from "../logic/types";
+
+	let {
+		field,
+		surfaceId,
+		onInvoke,
+	}: { field: ButtonFieldView; surfaceId: string; onInvoke: (msg: InvokeMessage) => void } =
+		$props();
+
+	function handleClick() {
+		onInvoke({
+			type: "invoke",
+			surfaceId,
+			actionId: field.action.actionId,
+		});
+	}
+</script>
+
+<button onclick={handleClick}>{field.label}</button>