diff --git a/comfy_api_nodes/util/client.py b/comfy_api_nodes/util/client.py
index 052301c33..b32075d43 100644
--- a/comfy_api_nodes/util/client.py
+++ b/comfy_api_nodes/util/client.py
@@ -51,7 +51,7 @@ class ApiEndpoint:
 
 @dataclass
 class _RequestConfig:
-    node_cls: type[IO.ComfyNode]
+    node_cls: type[IO.ComfyNode] | None
     endpoint: ApiEndpoint
     timeout: float
     content_type: str
@@ -70,6 +70,17 @@ class _RequestConfig:
     price_extractor: Callable[[dict[str, Any]], float | None] | None = None
     is_rate_limited: Callable[[int, Any], bool] | None = None
     response_header_validator: Callable[[dict[str, str]], None] | None = None
+    base_url: str | None = None
+    auth_headers: dict[str, str] | None = None
+    allow_304: bool = False
+    error_parser: Callable[[int, Any], Exception | None] | None = None
+    # Optional callback to render a per-second progress label while
+    # waiting out a rate-limit / SERVER_BUSY / MAINTENANCE retry. Called
+    # with ``(status, body, retry_after_s)`` and should return the label
+    # string used by ``_display_time_progress`` (which renders it as
+    # ``Status: <label>\nTime elapsed: Ns``). Returning ``None`` keeps
+    # the default ``cfg.wait_label``.
+    rate_limit_label: Callable[[int, Any, float], str | None] | None = None
 
 
 @dataclass
@@ -84,13 +95,40 @@ class _PollUIState:
 
 
 _RETRY_STATUS = {408, 500, 502, 503, 504}  # status 429 is handled separately
+
+
+def _parse_retry_after(raw: str | None) -> float | None:
+    """RFC 7231 Retry-After: seconds-int or HTTP-date.
+
+    Returns the wait time in seconds, clamped to non-negative. Returns
+    ``None`` for unparseable / missing values so the caller can fall
+    back to the local backoff schedule.
+    """
+    if not raw:
+        return None
+    raw = raw.strip()
+    try:
+        return max(0.0, float(raw))
+    except (TypeError, ValueError):
+        pass
+    # HTTP-date form (rare in practice for our servers, but cheap to support).
+    try:
+        from email.utils import parsedate_to_datetime
+        dt = parsedate_to_datetime(raw)
+        if dt is None:
+            return None
+        import datetime as _dt
+        now = _dt.datetime.now(tz=dt.tzinfo) if dt.tzinfo else _dt.datetime.utcnow()
+        return max(0.0, (dt - now).total_seconds())
+    except Exception:
+        return None
 COMPLETED_STATUSES = ["succeeded", "succeed", "success", "completed", "finished", "done", "complete"]
 FAILED_STATUSES = ["cancelled", "canceled", "canceling", "fail", "failed", "error"]
 QUEUED_STATUSES = ["created", "queued", "queueing", "submitted", "initializing", "wait"]
 
 
 async def sync_op(
-    cls: type[IO.ComfyNode],
+    cls: type[IO.ComfyNode] | None,
     endpoint: ApiEndpoint,
     *,
     response_model: type[M],
@@ -110,6 +148,9 @@ async def sync_op(
     monitor_progress: bool = True,
     max_retries_on_rate_limit: int = 16,
     is_rate_limited: Callable[[int, Any], bool] | None = None,
+    rate_limit_label: Callable[[int, Any, float], str | None] | None = None,
+    base_url: str | None = None,
+    auth_headers: dict[str, str] | None = None,
 ) -> M:
     raw = await sync_op_raw(
         cls,
@@ -131,6 +172,9 @@ async def sync_op(
         monitor_progress=monitor_progress,
         max_retries_on_rate_limit=max_retries_on_rate_limit,
         is_rate_limited=is_rate_limited,
+        rate_limit_label=rate_limit_label,
+        base_url=base_url,
+        auth_headers=auth_headers,
     )
     if not isinstance(raw, dict):
         raise Exception("Expected JSON response to validate into a Pydantic model, got non-JSON (binary or text).")
@@ -138,7 +182,7 @@ async def sync_op(
 
 
 async def poll_op(
-    cls: type[IO.ComfyNode],
+    cls: type[IO.ComfyNode] | None,
     poll_endpoint: ApiEndpoint,
     *,
     response_model: type[M],
@@ -159,6 +203,11 @@ async def poll_op(
     cancel_endpoint: ApiEndpoint | None = None,
     cancel_timeout: float = 10.0,
     extra_text: str | None = None,
+    base_url: str | None = None,
+    auth_headers: dict[str, str] | None = None,
+    error_parser: Callable[[int, Any], Exception | None] | None = None,
+    is_rate_limited: Callable[[int, Any], bool] | None = None,
+    rate_limit_label: Callable[[int, Any, float], str | None] | None = None,
 ) -> M:
     raw = await poll_op_raw(
         cls,
@@ -180,6 +229,11 @@ async def poll_op(
         cancel_endpoint=cancel_endpoint,
         cancel_timeout=cancel_timeout,
         extra_text=extra_text,
+        base_url=base_url,
+        auth_headers=auth_headers,
+        error_parser=error_parser,
+        is_rate_limited=is_rate_limited,
+        rate_limit_label=rate_limit_label,
     )
     if not isinstance(raw, dict):
         raise Exception("Expected JSON response to validate into a Pydantic model, got non-JSON (binary or text).")
@@ -187,7 +241,7 @@ async def poll_op(
 
 
 async def sync_op_raw(
-    cls: type[IO.ComfyNode],
+    cls: type[IO.ComfyNode] | None,
     endpoint: ApiEndpoint,
     *,
     price_extractor: Callable[[dict[str, Any]], float | None] | None = None,
@@ -207,13 +261,26 @@ async def sync_op_raw(
     monitor_progress: bool = True,
     max_retries_on_rate_limit: int = 16,
     is_rate_limited: Callable[[int, Any], bool] | None = None,
+    rate_limit_label: Callable[[int, Any, float], str | None] | None = None,
     response_header_validator: Callable[[dict[str, str]], None] | None = None,
-) -> dict[str, Any] | bytes:
+    base_url: str | None = None,
+    auth_headers: dict[str, str] | None = None,
+    allow_304: bool = False,
+    error_parser: Callable[[int, Any], Exception | None] | None = None,
+) -> dict[str, Any] | bytes | None:
     """
     Make a single network request.
       - If as_binary=False (default): returns JSON dict (or {'_raw': '<text>'} if non-JSON).
       - If as_binary=True: returns bytes.
       - response_header_validator: optional callback receiving response headers dict
+      - base_url: override the default api.comfy.org base for this request.
+      - auth_headers: pre-built Authorization/X-API-KEY dict; bypasses get_auth_header.
+      - allow_304: when True, an HTTP 304 response returns ``None`` instead of raising.
+      - error_parser: when set, called on every >=400 response with
+        ``(status, body)``; if it returns an Exception, that exception
+        is raised immediately and the retry/friendly-message path is
+        skipped. Used by RNP to surface structured ``RnpProtocolError``
+        envelopes that would otherwise be flattened to "API Error: ...".
     """
     if isinstance(data, BaseModel):
         data = data.model_dump(exclude_none=True)
@@ -239,13 +306,18 @@ async def sync_op_raw(
         price_extractor=price_extractor,
         max_retries_on_rate_limit=max_retries_on_rate_limit,
         is_rate_limited=is_rate_limited,
+        rate_limit_label=rate_limit_label,
         response_header_validator=response_header_validator,
+        base_url=base_url,
+        auth_headers=auth_headers,
+        allow_304=allow_304,
+        error_parser=error_parser,
     )
     return await _request_base(cfg, expect_binary=as_binary)
 
 
 async def poll_op_raw(
-    cls: type[IO.ComfyNode],
+    cls: type[IO.ComfyNode] | None,
     poll_endpoint: ApiEndpoint,
     *,
     status_extractor: Callable[[dict[str, Any]], str | int | None],
@@ -265,6 +337,11 @@ async def poll_op_raw(
     cancel_endpoint: ApiEndpoint | None = None,
     cancel_timeout: float = 10.0,
     extra_text: str | None = None,
+    base_url: str | None = None,
+    auth_headers: dict[str, str] | None = None,
+    error_parser: Callable[[int, Any], Exception | None] | None = None,
+    is_rate_limited: Callable[[int, Any], bool] | None = None,
+    rate_limit_label: Callable[[int, Any, float], str | None] | None = None,
 ) -> dict[str, Any]:
     """
     Polls an endpoint until the task reaches a terminal state. Displays time while queued/processing,
@@ -272,6 +349,14 @@ async def poll_op_raw(
 
     Uses default complete, failed and queued states assumption.
 
+    ``error_parser`` and ``is_rate_limited`` are forwarded to each
+    per-poll ``sync_op_raw`` call so callers can surface a typed
+    exception for >=400 responses (e.g. an RNP structured-error
+    envelope) and treat protocol-specific 5xx codes (e.g. RNP
+    ``SERVER_BUSY`` / ``MAINTENANCE``) like a 429 — both honour
+    ``Retry-After`` and consume the rate-limit retry counter instead
+    of falling through the generic 5xx exponential-backoff path.
+
     Returns the final JSON response from the poll endpoint.
     """
     completed_states = _normalize_statuses(COMPLETED_STATUSES if completed_statuses is None else completed_statuses)
@@ -286,6 +371,22 @@ async def poll_op_raw(
     state = _PollUIState(started=started, estimated_duration=estimated_duration)
     stop_ticker = asyncio.Event()
 
+    # Wrap the user's rate_limit_label so a SERVER_BUSY/MAINTENANCE/429
+    # wait inside the per-poll sync_op_raw also flips the outer ticker's
+    # status_label — otherwise _ticker keeps writing "Status: Queued"
+    # over our message every second. The next successful poll resets
+    # status_label from the response, so no manual restore is needed.
+    user_rate_limit_label = rate_limit_label
+
+    def _wrapped_rate_limit_label(status: int, body: Any, retry_after_s: float) -> str | None:
+        label: str | None = None
+        if user_rate_limit_label is not None:
+            with contextlib.suppress(Exception):
+                label = user_rate_limit_label(status, body, retry_after_s)
+        if label:
+            state.status_label = label
+        return label
+
     async def _ticker():
         """Emit a UI update every second while polling is in progress."""
         try:
@@ -327,6 +428,11 @@ async def poll_op_raw(
                     as_binary=False,
                     final_label_on_success=None,
                     monitor_progress=False,
+                    base_url=base_url,
+                    auth_headers=auth_headers,
+                    error_parser=error_parser,
+                    is_rate_limited=is_rate_limited,
+                    rate_limit_label=_wrapped_rate_limit_label,
                 )
                 if not isinstance(resp_json, dict):
                     raise Exception("Polling endpoint returned non-JSON response.")
@@ -343,6 +449,8 @@ async def poll_op_raw(
                             as_binary=False,
                             final_label_on_success=None,
                             monitor_progress=False,
+                            base_url=base_url,
+                            auth_headers=auth_headers,
                         )
                 raise
 
@@ -419,6 +527,8 @@ async def poll_op_raw(
                             as_binary=False,
                             final_label_on_success=None,
                             monitor_progress=False,
+                            base_url=base_url,
+                            auth_headers=auth_headers,
                         )
                 raise
             if not is_queued:
@@ -433,6 +543,16 @@ async def poll_op_raw(
     except (LocalNetworkError, ApiServerError):
         raise
     except Exception as e:
+        # Let typed protocol errors raised by ``error_parser`` (e.g.
+        # RnpProtocolError) bubble unchanged so callers can pattern-
+        # match on ``.code`` to drive resume / fallback logic. Any
+        # exception that exposes a string ``code`` attribute counts as
+        # "typed" — duck-typing avoids importing the typed-error class
+        # into this generic util layer. Everything else gets the
+        # friendlier wrapper for back-compat with existing api-node
+        # callers that surface the wrapped message directly to users.
+        if isinstance(getattr(e, "code", None), str):
+            raise
         raise Exception(f"Polling aborted due to error: {e}") from e
     finally:
         stop_ticker.set()
@@ -441,12 +561,16 @@ async def poll_op_raw(
 
 
 def _display_text(
-    node_cls: type[IO.ComfyNode],
+    node_cls: type[IO.ComfyNode] | None,
     text: str | None,
     *,
     status: str | int | None = None,
     price: float | None = None,
 ) -> None:
+    # Skip when there's no node to address — RNP / bootstrap callers
+    # pass cls=None on requests that aren't tied to a workflow node.
+    if node_cls is None:
+        return
     display_lines: list[str] = []
     if status:
         display_lines.append(f"Status: {status.capitalize() if isinstance(status, str) else status}")
@@ -461,7 +585,7 @@ def _display_text(
 
 
 def _display_time_progress(
-    node_cls: type[IO.ComfyNode],
+    node_cls: type[IO.ComfyNode] | None,
     status: str | int | None,
     elapsed_seconds: int,
     estimated_total: int | None = None,
@@ -481,7 +605,7 @@ def _display_time_progress(
     _display_text(node_cls, text, status=status, price=price)
 
 
-async def _diagnose_connectivity() -> dict[str, bool]:
+async def _diagnose_connectivity(base_url: str | None = None) -> dict[str, bool]:
     """Best-effort connectivity diagnostics to distinguish local vs. server issues."""
     results = {
         "internet_accessible": False,
@@ -515,7 +639,7 @@ async def _diagnose_connectivity() -> dict[str, bool]:
         if not results["internet_accessible"]:
             return results
 
-        parsed = urlparse(default_base_url())
+        parsed = urlparse(base_url or default_base_url())
         health_url = f"{parsed.scheme}://{parsed.netloc}/health"
         with contextlib.suppress(ClientError, OSError):
             async with session.get(health_url) as resp:
@@ -604,10 +728,11 @@ def _snapshot_request_body_for_logging(
 
 async def _request_base(cfg: _RequestConfig, expect_binary: bool):
     """Core request with retries, per-second interruption monitoring, true cancellation, and friendly errors."""
+    resolved_base_url = cfg.base_url or default_base_url()
     url = cfg.endpoint.path
     parsed_url = urlparse(url)
     if not parsed_url.scheme and not parsed_url.netloc:  # is URL relative?
-        url = urljoin(default_base_url().rstrip("/") + "/", url.lstrip("/"))
+        url = urljoin(resolved_base_url.rstrip("/") + "/", url.lstrip("/"))
 
     method = cfg.endpoint.method
     params = _merge_params(cfg.endpoint.query_params, method, cfg.data if method == "GET" else None)
@@ -645,7 +770,10 @@ async def _request_base(cfg: _RequestConfig, expect_binary: bool):
 
         payload_headers = {"Accept": "*/*"} if expect_binary else {"Accept": "application/json"}
         if not parsed_url.scheme and not parsed_url.netloc:  # is URL relative?
-            payload_headers.update(get_auth_header(cfg.node_cls))
+            if cfg.auth_headers is not None:
+                payload_headers.update(cfg.auth_headers)
+            elif cfg.node_cls is not None:
+                payload_headers.update(get_auth_header(cfg.node_cls))
             payload_headers["Comfy-Env"] = get_deploy_environment()
         if cfg.endpoint.headers:
             payload_headers.update(cfg.endpoint.headers)
@@ -726,6 +854,21 @@ async def _request_base(cfg: _RequestConfig, expect_binary: bool):
             # Otherwise, request finished
             resp = await req_task
             async with resp:
+                if cfg.allow_304 and resp.status == 304:
+                    resp_headers = {k.lower(): v for k, v in resp.headers.items()}
+                    if cfg.response_header_validator:
+                        cfg.response_header_validator(resp_headers)
+                    operation_succeeded = True
+                    final_elapsed_seconds = int(time.monotonic() - start_time)
+                    request_logger.log_request_response(
+                        operation_id=operation_id,
+                        request_method=method,
+                        request_url=url,
+                        response_status_code=resp.status,
+                        response_headers=resp_headers,
+                        response_content=None,
+                    )
+                    return None
                 if resp.status >= 400:
                     try:
                         body = await resp.json()
@@ -737,12 +880,33 @@ async def _request_base(cfg: _RequestConfig, expect_binary: bool):
                     is_rl = resp.status == 429 or (
                         cfg.is_rate_limited is not None and cfg.is_rate_limited(resp.status, body)
                     )
+                    sleep_label = cfg.wait_label
                     if is_rl and rate_limit_attempts < cfg.max_retries_on_rate_limit:
                         rate_limit_attempts += 1
-                        wait_time = min(rate_limit_delay, 30.0)
+                        # Honor server-provided Retry-After when present
+                        # (clamped to keep a runaway header from blocking
+                        # the executor for hours), otherwise fall back to
+                        # the local exponential backoff.
+                        retry_after_s = _parse_retry_after(resp.headers.get("Retry-After"))
+                        if retry_after_s is not None:
+                            wait_time = min(retry_after_s, 300.0)
+                        else:
+                            wait_time = min(rate_limit_delay, 30.0)
                         rate_limit_delay *= cfg.retry_backoff
                         retry_label = f"rate-limit retry {rate_limit_attempts} of {cfg.max_retries_on_rate_limit}"
                         should_retry = True
+                        # Let callers (e.g. RNP) render a friendlier
+                        # per-second label like
+                        # "Server busy, retrying in 30s..." while we
+                        # sleep — surfaced via send_progress_text by
+                        # _display_time_progress every second.
+                        if cfg.rate_limit_label is not None:
+                            with contextlib.suppress(Exception):
+                                custom = cfg.rate_limit_label(
+                                    resp.status, body, wait_time
+                                )
+                                if custom:
+                                    sleep_label = custom
                     elif resp.status in _RETRY_STATUS and (attempt - rate_limit_attempts) <= cfg.max_retries:
                         wait_time = delay
                         delay *= cfg.retry_backoff
@@ -767,15 +931,45 @@ async def _request_base(cfg: _RequestConfig, expect_binary: bool):
                             response_content=body,
                             error_message=f"HTTP {resp.status} ({retry_label}, will retry in {wait_time:.1f}s)",
                         )
+                        # Stop the in-flight monitor so the per-second
+                        # progress label flips from cfg.wait_label
+                        # ("Waiting for server") to the rate-limit copy
+                        # ("Server busy, retrying in Ns...") for the
+                        # duration of this sleep — otherwise the two
+                        # writers race and the user sees alternating
+                        # text every tick.
+                        stop_event.set()
+                        if monitor_task:
+                            monitor_task.cancel()
+                            with contextlib.suppress(Exception):
+                                await monitor_task
+                            monitor_task = None
                         await sleep_with_interrupt(
                             wait_time,
                             cfg.node_cls,
-                            cfg.wait_label if cfg.monitor_progress else None,
+                            sleep_label if cfg.monitor_progress else None,
                             start_time if cfg.monitor_progress else None,
                             cfg.estimated_total,
                             display_callback=_display_time_progress if cfg.monitor_progress else None,
                         )
                         continue
+                    # Retries either weren't applicable or have been exhausted —
+                    # give the caller's error_parser a chance to surface a
+                    # structured exception (e.g. RNP RnpProtocolError) before
+                    # we flatten the response with _friendly_http_message.
+                    if cfg.error_parser is not None:
+                        custom_exc = cfg.error_parser(resp.status, body)
+                        if custom_exc is not None:
+                            request_logger.log_request_response(
+                                operation_id=operation_id,
+                                request_method=method,
+                                request_url=url,
+                                response_status_code=resp.status,
+                                response_headers=dict(resp.headers),
+                                response_content=body,
+                                error_message=f"{type(custom_exc).__name__}: {custom_exc}",
+                            )
+                            raise custom_exc
                     msg = _friendly_http_message(resp.status, body)
                     request_logger.log_request_response(
                         operation_id=operation_id,
@@ -878,7 +1072,7 @@ async def _request_base(cfg: _RequestConfig, expect_binary: bool):
                 )
                 delay *= cfg.retry_backoff
                 continue
-            diag = await _diagnose_connectivity()
+            diag = await _diagnose_connectivity(resolved_base_url)
             if not diag["internet_accessible"]:
                 request_logger.log_request_response(
                     operation_id=operation_id,
@@ -903,7 +1097,7 @@ async def _request_base(cfg: _RequestConfig, expect_binary: bool):
                 error_message=f"ApiServerError: {str(e)}",
             )
             raise ApiServerError(
-                f"The API server at {default_base_url()} is currently unreachable. "
+                f"The API server at {resolved_base_url} is currently unreachable. "
                 f"The service may be experiencing issues."
             ) from e
         finally: