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, 56 insertions, 0 deletions

diff --git a/src/app/resolve-http-url.test.ts b/src/app/resolve-http-url.test.ts
new file mode 100644
index 0000000..d465d70
--- /dev/null
+++ b/src/app/resolve-http-url.test.ts
@@ -0,0 +1,56 @@
+import { describe, expect, it } from "vitest";
+import { resolveHttpUrl } from "./resolve-http-url";
+
+describe("resolveHttpUrl", () => {
+	it("explicit url wins over everything", () => {
+		const result = resolveHttpUrl(
+			{ VITE_HTTP_URL: "https://env.example.com:9999" },
+			{ protocol: "https:", hostname: "page.example.com" },
+		);
+		expect(result).toBe("https://env.example.com:9999");
+	});
+
+	it("VITE_HTTP_URL wins over derivation", () => {
+		const result = resolveHttpUrl(
+			{ VITE_HTTP_URL: "https://env.example.com:8888" },
+			{ protocol: "http:", hostname: "page.example.com" },
+		);
+		expect(result).toBe("https://env.example.com:8888");
+	});
+
+	it("derives http://<hostname>:24203 from http location", () => {
+		const result = resolveHttpUrl({}, { protocol: "http:", hostname: "PII_REDACTED_DEV_IPV4_01" });
+		expect(result).toBe("http://PII_REDACTED_DEV_IPV4_01:24203");
+	});
+
+	it("derives https://<hostname>:24203 from https location", () => {
+		const result = resolveHttpUrl({}, { protocol: "https:", hostname: "PII_REDACTED_DEVICE_01" });
+		expect(result).toBe("https://PII_REDACTED_DEVICE_01:24203");
+	});
+
+	it("uses VITE_HTTP_PORT when set", () => {
+		const result = resolveHttpUrl(
+			{ VITE_HTTP_PORT: "3000" },
+			{ protocol: "http:", hostname: "localhost" },
+		);
+		expect(result).toBe("http://localhost:3000");
+	});
+
+	it("falls back to http://localhost:24203 when location is missing", () => {
+		const result = resolveHttpUrl({});
+		expect(result).toBe("http://localhost:24203");
+	});
+
+	it("VITE_HTTP_URL empty string treated as unset", () => {
+		const result = resolveHttpUrl({ VITE_HTTP_URL: "" }, { protocol: "http:", hostname: "myhost" });
+		expect(result).toBe("http://myhost:24203");
+	});
+
+	it("VITE_HTTP_PORT empty string falls back to default", () => {
+		const result = resolveHttpUrl(
+			{ VITE_HTTP_PORT: "" },
+			{ protocol: "http:", hostname: "localhost" },
+		);
+		expect(result).toBe("http://localhost:24203");
+	});
+});