refactor(web): extract isTauri into a leaf platform module

packages/web/src/lib/discovery.ts

@@ -1,14 +1,13 @@
 import { httpFetch } from "@/lib/http";
+import { isTauri } from "@/lib/platform";
+
+export { isTauri } from "@/lib/platform";
 
 export interface DiscoveredInstance {
 	port: number;
 	base_url: string;
 }
 
-export function isTauri(): boolean {
-	return typeof window !== "undefined" && "__TAURI_INTERNALS__" in window;
-}
-
 /**
  * Probe localhost ports for running Honcho instances. Desktop-only — the web
  * build can't port-scan due to CORS, so this returns an empty list when not

packages/web/src/lib/http.ts

@@ -1,12 +1,8 @@
 import { fetch as tauriFetch } from "@tauri-apps/plugin-http";
+import { isTauri } from "@/lib/platform";
 
 // Route fetch through Rust (reqwest) when running in Tauri — bypasses WebView CORS enforcement.
-// Falls back to native browser fetch during plain web dev (`pnpm dev:web`).
-const isTauri = Boolean(
-	typeof window !== "undefined" &&
-		(window as unknown as Record<string, unknown>).__TAURI_INTERNALS__,
-);
-
-export const httpFetch: typeof globalThis.fetch = isTauri
+// Falls back to native browser fetch during plain web dev.
+export const httpFetch: typeof globalThis.fetch = isTauri()
 	? (tauriFetch as typeof globalThis.fetch)
 	: globalThis.fetch;

packages/web/src/lib/platform.ts

@@ -0,0 +1,4 @@
+/** True when running inside the Tauri desktop shell (WebView with injected internals). */
+export function isTauri(): boolean {
+	return typeof window !== "undefined" && "__TAURI_INTERNALS__" in window;
+}

packages/web/src/test/platform.test.ts

@@ -0,0 +1,17 @@
+import { afterEach, describe, expect, it } from "vitest";
+import { isTauri } from "@/lib/platform";
+
+describe("isTauri", () => {
+	afterEach(() => {
+		delete (window as unknown as Record<string, unknown>).__TAURI_INTERNALS__;
+	});
+
+	it("returns false in a plain browser/jsdom environment", () => {
+		expect(isTauri()).toBe(false);
+	});
+
+	it("returns true when the Tauri internals global is present", () => {
+		(window as unknown as Record<string, unknown>).__TAURI_INTERNALS__ = {};
+		expect(isTauri()).toBe(true);
+	});
+});