fix(client): rewrite absolute fetch/EventSource paths under basePath (#8515)

* fix(client): rewrite absolute fetch/EventSource paths under basePath

Absolute browser calls like fetch("/api/...") and new EventSource("/api/...")
do not honor Next.js basePath, so subpath deploys (OMNIROUTE_BASE_PATH) break
dashboard health checks, settings APIs, and SSE unless a reverse proxy rewrites
the domain root.

- Add withBasePath / getDeployBasePath helpers
- Install ref-counted fetch + EventSource rewrite when basePath is set
  (same pattern as installDashboardCsrfFetch)
- Mount BasePathNetworkProvider at the root so login works too
- Mirror OMNIROUTE_BASE_PATH to NEXT_PUBLIC_OMNIROUTE_BASE_PATH for the client
- Document in .env.example; unit tests for rewrite rules

* docs(changelog): add fragment for #8515 basePath client fetch

* test(client): move basePath tests into a scanned dir and fix no-op call-shape asserts

Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>

* fix(client-sweep-8515): restore CHANGELOG #8471 bullet and fix basePath TS2322

Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>

---------

Co-authored-by: rqzbeh <rqzbeh@users.noreply.github.com>
Co-authored-by: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>
Co-authored-by: Diego Rodrigues de Sa e Souza <diegosouza.pw@gmail.com>
Co-authored-by: diegosouzapw <diegosouzapw@users.noreply.github.com>

src/shared/utils/basePathFetch.ts

@@ -0,0 +1,96 @@
+/**
+ * Install a same-origin fetch + EventSource rewrite for Next.js basePath deploys.
+ *
+ * Pattern mirrors `installDashboardCsrfFetch` (ref-counted global wrap).
+ * Only activates when `NEXT_PUBLIC_OMNIROUTE_BASE_PATH` / `OMNIROUTE_BASE_PATH` is set.
+ */
+
+import { getDeployBasePath, withBasePath } from "./basePath";
+
+let originalFetch: typeof fetch | null = null;
+let originalEventSource: typeof EventSource | null = null;
+let installCount = 0;
+
+export function __resetBasePathFetchForTests(): void {
+  if (originalFetch) {
+    globalThis.fetch = originalFetch;
+    originalFetch = null;
+  }
+  if (originalEventSource && typeof window !== "undefined") {
+    window.EventSource = originalEventSource;
+    originalEventSource = null;
+  }
+  installCount = 0;
+}
+
+function rewriteInput(input: RequestInfo | URL, basePath: string): RequestInfo | URL {
+  if (typeof input === "string") {
+    return withBasePath(input, basePath);
+  }
+  if (typeof URL !== "undefined" && input instanceof URL) {
+    return new URL(withBasePath(input.href, basePath));
+  }
+  if (typeof Request !== "undefined" && input instanceof Request) {
+    const rewritten = withBasePath(input.url, basePath);
+    if (rewritten === input.url) return input;
+    return new Request(rewritten, input);
+  }
+  return input;
+}
+
+/**
+ * Wrap `globalThis.fetch` (and `EventSource` in the browser) so absolute
+ * same-origin app paths receive the Next.js basePath prefix.
+ *
+ * No-op when basePath is empty (root deploys). Safe to call multiple times;
+ * uninstall when the last consumer unmounts.
+ */
+export function installBasePathFetch(
+  basePath: string = getDeployBasePath()
+): () => void {
+  if (!basePath) return () => {};
+  if (typeof globalThis.fetch !== "function") return () => {};
+
+  if (installCount === 0) {
+    originalFetch = globalThis.fetch.bind(globalThis);
+
+    globalThis.fetch = ((input: RequestInfo | URL, init?: RequestInit) => {
+      if (!originalFetch) return fetch(input, init);
+      return originalFetch(rewriteInput(input, basePath), init);
+    }) as typeof fetch;
+
+    if (typeof window !== "undefined" && typeof window.EventSource === "function") {
+      originalEventSource = window.EventSource;
+      const BaseES = originalEventSource;
+
+      // Subclass so `instanceof EventSource` and prototype methods keep working.
+      class BasePathEventSource extends BaseES {
+        constructor(url: string | URL, eventSourceInitDict?: EventSourceInit) {
+          const raw = typeof url === "string" ? url : url.toString();
+          super(withBasePath(raw, basePath), eventSourceInitDict);
+        }
+      }
+
+      window.EventSource = BasePathEventSource as typeof EventSource;
+    }
+  }
+
+  installCount++;
+  let active = true;
+
+  return () => {
+    if (!active) return;
+    active = false;
+    installCount = Math.max(0, installCount - 1);
+    if (installCount === 0) {
+      if (originalFetch) {
+        globalThis.fetch = originalFetch;
+        originalFetch = null;
+      }
+      if (originalEventSource && typeof window !== "undefined") {
+        window.EventSource = originalEventSource;
+        originalEventSource = null;
+      }
+    }
+  };
+}