Implement Monlet MVP stack and UI updates

server/monlet_server/errors.py

@@ -0,0 +1,54 @@
+from fastapi import FastAPI, Request
+from fastapi.exceptions import RequestValidationError
+from fastapi.responses import JSONResponse
+from starlette.exceptions import HTTPException as StarletteHTTPException
+
+from .logging_config import get_logger, request_id_var
+from .schemas import ErrorBody, ErrorCode, ErrorResponse
+
+log = get_logger("monlet.errors")
+
+
+def _request_id(request: Request) -> str:
+    rid = getattr(request.state, "request_id", None)
+    if rid is None:
+        rid = request_id_var.get() or ""
+    return rid
+
+
+def error_response(
+    request: Request, status_code: int, code: ErrorCode, message: str
+) -> JSONResponse:
+    body = ErrorResponse(
+        error=ErrorBody(code=code, message=message, request_id=_request_id(request))
+    )
+    return JSONResponse(status_code=status_code, content=body.model_dump())
+
+
+_STATUS_TO_CODE: dict[int, ErrorCode] = {
+    400: "validation",
+    401: "unauthorized",
+    404: "not_found",
+    413: "payload_too_large",
+    429: "rate_limited",
+    500: "internal",
+    503: "not_ready",
+}
+
+
+def install_error_handlers(app: FastAPI) -> None:
+    @app.exception_handler(RequestValidationError)
+    async def _validation(request: Request, exc: RequestValidationError):
+        message = "request validation failed"
+        return error_response(request, 400, "validation", message)
+
+    @app.exception_handler(StarletteHTTPException)
+    async def _http(request: Request, exc: StarletteHTTPException):
+        code = _STATUS_TO_CODE.get(exc.status_code, "internal")
+        msg = exc.detail if isinstance(exc.detail, str) else code
+        return error_response(request, exc.status_code, code, msg)
+
+    @app.exception_handler(Exception)
+    async def _unhandled(request: Request, exc: Exception):
+        log.exception("unhandled_exception", error=type(exc).__name__)
+        return error_response(request, 500, "internal", "internal server error")