feat(scripts): local frontend dev server with prod backend proxy

Serves web/ from the working tree and forwards the data and chat
routes to the live deployment, so uncommitted frontend and prompt
changes can be exercised against the real model and corpus before any
image bake. Prompt-behavior changes were previously only testable
post-deploy (~15 min per iteration).

  python scripts/web_dev_proxy.py   # http://127.0.0.1:8765

Author: NorthernLightx

scripts/web_dev_proxy.py

@@ -0,0 +1,59 @@
+"""Local web/ with the PROD backend proxied behind it.
+
+Serves the working-tree frontend while forwarding /health /papers /figures
+/pages/* /query /demo/chat to the live deployment — full end-to-end testing
+of uncommitted client code against the real model and corpus, no deploy.
+"""
+
+import functools
+import http.server
+import urllib.error
+import urllib.request
+from pathlib import Path
+
+PROD = "https://spectrarag-ar6wxit42a-ew.a.run.app"
+ROOT = str(Path(__file__).resolve().parents[1] / "web")
+
+
+class H(http.server.SimpleHTTPRequestHandler):
+    protocol_version = "HTTP/1.0"  # close-delimited responses, safe for SSE relay
+
+    def _proxy(self) -> None:
+        data = None
+        if self.command == "POST":
+            data = self.rfile.read(int(self.headers.get("Content-Length", 0)))
+        req = urllib.request.Request(PROD + self.path, data=data, method=self.command)
+        req.add_header("Content-Type", self.headers.get("Content-Type", "application/json"))
+        try:
+            with urllib.request.urlopen(req, timeout=180) as r:
+                self.send_response(r.status)
+                self.send_header("Content-Type", r.headers.get("Content-Type", "application/json"))
+                self.end_headers()
+                while True:
+                    chunk = r.read(1024)
+                    if not chunk:
+                        break
+                    self.wfile.write(chunk)
+                    self.wfile.flush()
+        except urllib.error.HTTPError as e:
+            body = e.read()
+            self.send_response(e.code)
+            self.send_header("Content-Type", "application/json")
+            self.send_header("Content-Length", str(len(body)))
+            self.end_headers()
+            self.wfile.write(body)
+
+    def do_GET(self) -> None:
+        if self.path.startswith(("/health", "/papers", "/figures", "/pages/")):
+            return self._proxy()
+        super().do_GET()
+
+    def do_POST(self) -> None:
+        if self.path.startswith(("/query", "/demo/chat")):
+            return self._proxy()
+        self.send_error(404)
+
+
+http.server.ThreadingHTTPServer(
+    ("127.0.0.1", 8765), functools.partial(H, directory=ROOT)
+).serve_forever()