fix(ui): fix /ui/chat 404 — restructure heuristic false-positive + pre-restructure in Dockerfile

Starlette StaticFiles(html=True) serves extensionless routes (e.g. /ui/chat)
by looking for {route}/index.html. Next.js static export generates login/index.html
for older pages but chat.html (root-level) for the new Chat UI page added in #22937.

The _is_ui_pre_restructured() fallback heuristic returned True as soon as it found
any {dir}/index.html (e.g. login/index.html), skipping the restructure step and
leaving chat.html in place — causing /ui/chat to 404.

Fix 1: proxy_server.py — tighten the heuristic to also scan for orphaned root-level
.html files; return False if any exist so restructuring runs.

Fix 2: Dockerfile — add pre-restructure step (matching Dockerfile.non_root) so the
main published image pre-moves all {page}.html → {page}/index.html and writes the
.litellm_ui_ready marker, bypassing the heuristic entirely on subsequent starts.

Dockerfile

@@ -24,6 +24,19 @@ COPY . .
 # Convert Windows line endings to Unix and make executable
 RUN sed -i 's/\r$//' docker/build_admin_ui.sh && chmod +x docker/build_admin_ui.sh && ./docker/build_admin_ui.sh
 
+# Pre-restructure UI: move root-level {page}.html → {page}/index.html so
+# Starlette StaticFiles can serve extensionless routes (e.g. /ui/chat).
+# Must run before building the wheel since the out/ dir is included in the package.
+RUN cd litellm/proxy/_experimental/out && \
+    for html_file in *.html; do \
+      if [ "$html_file" != "index.html" ] && [ "$html_file" != "404.html" ] && [ -f "$html_file" ]; then \
+        folder_name="${html_file%.html}" && \
+        mkdir -p "$folder_name" && \
+        mv "$html_file" "$folder_name/index.html"; \
+      fi; \
+    done && \
+    touch .litellm_ui_ready
+
 # Build the package
 RUN rm -rf dist/* && python -m build
 

litellm/proxy/proxy_server.py

@@ -1203,7 +1203,27 @@ try:
                 if entry.is_dir() and not entry.name.startswith("_"):
                     index_path = os.path.join(entry.path, "index.html")
                     if os.path.exists(index_path):
-                        # Found at least one restructured route - this proves the pattern
+                        # Found at least one restructured route.
+                        # Also verify no root-level .html files still need restructuring.
+                        # Next.js static export may generate both pre-restructured pages
+                        # (e.g. login/index.html) and new pages as root-level .html files
+                        # (e.g. chat.html), causing the heuristic to fire prematurely.
+                        try:
+                            orphaned = [
+                                e.name
+                                for e in os.scandir(ui_dir)
+                                if e.is_file()
+                                and e.name.endswith(".html")
+                                and e.name not in ("index.html", "404.html")
+                            ]
+                        except (PermissionError, OSError):
+                            orphaned = []
+                        if orphaned:
+                            verbose_proxy_logger.debug(
+                                f"Found un-restructured HTML files at root: {orphaned}. "
+                                f"Restructuring needed despite existing {entry.name}/index.html."
+                            )
+                            return False
                         verbose_proxy_logger.debug(
                             f"Detected restructured UI via pattern: found {entry.name}/index.html"
                         )