client: auto-detect server URL from request headers

app/api/routes.py

@@ -247,12 +247,38 @@ def _get_client_id() -> str | None:
 
 @bp.route("/client", methods=["GET"])
 def client():
-    """Download the fpaste CLI client."""
+    """Download the fpaste CLI client with server URL pre-configured."""
     import os
+
+    # Detect scheme (check reverse proxy headers first)
+    scheme = (
+        request.headers.get("X-Forwarded-Proto")
+        or request.headers.get("X-Scheme")
+        or request.scheme
+    )
+
+    # Detect host (check reverse proxy headers first)
+    host = (
+        request.headers.get("X-Forwarded-Host")
+        or request.headers.get("Host")
+        or request.host
+    )
+
+    # Build server URL with prefix
+    prefix = current_app.config.get("URL_PREFIX", "")
+    server_url = f"{scheme}://{host}{prefix}"
+
     client_path = os.path.join(current_app.root_path, "..", "fpaste")
     try:
         with open(client_path, "r") as f:
             content = f.read()
+
+        # Replace default server URL
+        content = content.replace(
+            '"server": os.environ.get("FLASKPASTE_SERVER", "http://localhost:5000")',
+            f'"server": os.environ.get("FLASKPASTE_SERVER", "{server_url}")',
+        )
+
         response = Response(content, mimetype="text/x-python")
         response.headers["Content-Disposition"] = "attachment; filename=fpaste"
         return response