Add better no-frontend-dir handling (and lint, whoops)

app/frontend_static.py

@@ -0,0 +1,73 @@
+import logging
+from pathlib import Path
+
+from fastapi import FastAPI, HTTPException
+from fastapi.responses import FileResponse
+from fastapi.staticfiles import StaticFiles
+
+logger = logging.getLogger(__name__)
+
+
+def register_frontend_static_routes(app: FastAPI, frontend_dir: Path) -> bool:
+    """Register frontend static file routes if a built frontend is available.
+
+    Returns True when routes are registered, False when frontend files are
+    missing/incomplete. Missing frontend files are logged but are not fatal.
+    """
+    frontend_dir = frontend_dir.resolve()
+    index_file = frontend_dir / "index.html"
+    assets_dir = frontend_dir / "assets"
+
+    if not frontend_dir.exists():
+        logger.error(
+            "Frontend build directory not found at %s. "
+            "Run 'cd frontend && npm run build'. API will continue without frontend routes.",
+            frontend_dir,
+        )
+        return False
+
+    if not frontend_dir.is_dir():
+        logger.error(
+            "Frontend build path is not a directory: %s. "
+            "API will continue without frontend routes.",
+            frontend_dir,
+        )
+        return False
+
+    if not index_file.exists():
+        logger.error(
+            "Frontend index file not found at %s. "
+            "Run 'cd frontend && npm run build'. API will continue without frontend routes.",
+            index_file,
+        )
+        return False
+
+    if assets_dir.exists() and assets_dir.is_dir():
+        app.mount("/assets", StaticFiles(directory=assets_dir), name="assets")
+    else:
+        logger.warning(
+            "Frontend assets directory missing at %s; /assets files will not be served",
+            assets_dir,
+        )
+
+    @app.get("/")
+    async def serve_index():
+        """Serve the frontend index.html."""
+        return FileResponse(index_file)
+
+    @app.get("/{path:path}")
+    async def serve_frontend(path: str):
+        """Serve frontend files, falling back to index.html for SPA routing."""
+        file_path = (frontend_dir / path).resolve()
+        try:
+            file_path.relative_to(frontend_dir)
+        except ValueError:
+            raise HTTPException(status_code=404, detail="Not found") from None
+
+        if file_path.exists() and file_path.is_file():
+            return FileResponse(file_path)
+
+        return FileResponse(index_file)
+
+    logger.info("Serving frontend from %s", frontend_dir)
+    return True