feat(config): resolve the API base at runtime from config.js

index.html

@@ -11,6 +11,13 @@
   </head>
   <body>
     <div id="root"></div>
+    <!--
+      Runtime config, loaded before the app and deliberately not a module: a
+      classic script blocks until it has run, so window.__UDYAM_CONFIG__ is set
+      before any module code reads it. Served unbundled from the static root so
+      the API base can be changed on the server without rebuilding.
+    -->
+    <script src="/config.js"></script>
     <script type="module" src="/src/main.tsx"></script>
   </body>
 </html>

nginx.conf

@@ -19,6 +19,13 @@ server {
         add_header Cache-Control "no-cache, no-store, must-revalidate";
     }
 
+    # Runtime config — never cached. It is how the API base is changed without a
+    # rebuild, and a cached copy would silently pin the old URL for every browser
+    # that has already loaded the app, with no way to tell from the server side.
+    location = /config.js {
+        add_header Cache-Control "no-cache, no-store, must-revalidate";
+    }
+
     # The API, same-origin. The bundle is built with VITE_UDYAM_API_BASE_URL set
     # to the relative /api/v1/udyam, so it carries no hostname at all and the
     # same dist/ serves from any domain. That also puts the API on the UI's own

public/config.js

@@ -0,0 +1,30 @@
+/*
+ * Runtime configuration — edited on the server, not baked into the bundle.
+ *
+ * Vite inlines import.meta.env.VITE_* at build time, so a bundle built for one
+ * backend URL cannot be pointed at another without rebuilding. That is the wrong
+ * shape for a deployment where the backend goes up first and the UI follows, or
+ * where the same artifact is promoted from demo to staging. This file is served
+ * from the static root unbundled, so ops can change the API base and reload.
+ *
+ * Precedence, highest first:
+ *   1. apiBaseUrl below, if it is a non-empty string
+ *   2. VITE_UDYAM_API_BASE_URL, compiled in at build time
+ *   3. "/api/v1/udyam" — same-origin, which is what the nginx and httpd configs
+ *      in DEPLOYMENT.md set up
+ *
+ * Leave it empty for a same-origin deployment; that is the common case and needs
+ * no edit. Set it when the API lives on another host:
+ *
+ *   apiBaseUrl: "https://udyamlinc-api.lincpay.tech/api/v1/udyam"
+ *
+ * A cross-origin value also needs that origin in the backend's
+ * UDYAM_CORS_ALLOWED_ORIGINS, or the browser blocks every call while the API
+ * itself looks healthy.
+ *
+ * This file must never be cached — the server configs send no-store for it.
+ * Cached, it silently pins the old URL for anyone who has already loaded the app.
+ */
+window.__UDYAM_CONFIG__ = {
+  apiBaseUrl: '',
+}

src/lib/api.ts

@@ -1,8 +1,43 @@
 import axios from 'axios'
 
-/** udyamlinc-backend — Spring Boot skeleton, context path /api/v1/udyam. */
-export const API_BASE =
-  import.meta.env.VITE_UDYAM_API_BASE_URL ?? 'http://udyamlinc-backend.lincpay/api/v1/udyam'
+declare global {
+  interface Window {
+    __UDYAM_CONFIG__?: { apiBaseUrl?: string }
+  }
+}
+
+/**
+ * Where the API lives — resolved at runtime, not frozen into the bundle.
+ *
+ * <p>Precedence, highest first:
+ *
+ * 1. `window.__UDYAM_CONFIG__.apiBaseUrl` from `public/config.js`, which is served
+ *    unbundled and can be edited on the server. This is what lets the backend be
+ *    deployed first and the UI pointed at it afterwards, without a rebuild.
+ * 2. `VITE_UDYAM_API_BASE_URL`, inlined at build time — still useful for `npm run
+ *    dev` against a local backend.
+ * 3. `/api/v1/udyam` — relative, so the bundle carries no hostname, works from any
+ *    domain, and is same-origin with the API that nginx or httpd proxies. Being
+ *    same-origin also means CORS never applies, which removes the largest single
+ *    source of works-locally-fails-deployed.
+ *
+ * <p>An empty or whitespace-only value counts as unset. A deployment that writes
+ * `apiBaseUrl: ""` into config.js means "use the default", and treating that as a
+ * real base would send every request to the page's own URL.
+ */
+function resolveApiBase(): string {
+  const runtime = window.__UDYAM_CONFIG__?.apiBaseUrl
+  if (typeof runtime === 'string' && runtime.trim() !== '') {
+    return runtime.trim().replace(/\/+$/, '')
+  }
+  const compiled = import.meta.env.VITE_UDYAM_API_BASE_URL
+  if (typeof compiled === 'string' && compiled.trim() !== '') {
+    return compiled.trim().replace(/\/+$/, '')
+  }
+  return '/api/v1/udyam'
+}
+
+export const API_BASE = resolveApiBase()
 
 /** Short timeout: field devices are on patchy 2G and every screen has a local fallback. */
 export const api = axios.create({ baseURL: API_BASE, timeout: 6_000 })