Slice 2 wave 3: wire chat end-to-end at the composition root

- app/store.svelte.ts: one WebSocket carries surfaces AND chat (onChat ->
  chatStore.handleDelta); build the conversation cache over the IndexedDB
  adapter; createChatStore wired to transport (socket.send), injected HTTP
  historySync, and the cache; load() on construct
- app/resolve-http-url.ts: host-relative HTTP base (port 24203), mirrors
  resolve-ws-url; injected fetch
- App.svelte: render ChatView + Composer alongside the surface picker
- createAppStore gains optional injection points (httpUrl/fetchImpl/indexedDB/
  conversationId) for tests
- vitest-setup.ts: fake-indexeddb/auto for jsdom IndexedDB (orchestrator-owned
  config; agent change adopted)

Verified green (x2, stable): svelte-check 0/0, vitest 218, biome clean, build ok.
Slice 2 (conversation transcript: cache + delta streaming) feature-complete.

1 files changed, 28 insertions, 0 deletions

diff --git a/src/app/resolve-http-url.ts b/src/app/resolve-http-url.ts
new file mode 100644
index 0000000..357d2fc
--- /dev/null
+++ b/src/app/resolve-http-url.ts
@@ -0,0 +1,28 @@
+export interface HttpUrlEnv {
+	readonly VITE_HTTP_URL?: string;
+	readonly VITE_HTTP_PORT?: string;
+}
+
+export interface HttpUrlLocation {
+	readonly protocol: string;
+	readonly hostname: string;
+}
+
+const DEFAULT_PORT = "24203";
+const DEFAULT_FALLBACK = "http://localhost:24203";
+
+export function resolveHttpUrl(env: HttpUrlEnv, location?: HttpUrlLocation): string {
+	if (env.VITE_HTTP_URL !== undefined && env.VITE_HTTP_URL !== "") {
+		return env.VITE_HTTP_URL;
+	}
+
+	if (location === undefined) {
+		return DEFAULT_FALLBACK;
+	}
+
+	const port =
+		env.VITE_HTTP_PORT !== undefined && env.VITE_HTTP_PORT !== ""
+			? env.VITE_HTTP_PORT
+			: DEFAULT_PORT;
+	return `${location.protocol}//${location.hostname}:${port}`;
+}