diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index 4b95950db1..b4b96c611b 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -3424,11 +3424,14 @@ class _StreamingCall(StreamingWaitMonitor):
             self.agent._log_stream_retry(kind="exhausted", error=e, attempt=max_retries + 1,
                 max_attempts=max_retries + 1, mid_tool_call=False, diag=self.clients.diag)
             # Empty stream: "connection failed" would send users chasing network issues.
-            _what = ("Provider returned malformed streaming data after" if _is_stream_parse_err
-                     else "Provider returned an empty response stream after" if _is_empty_stream
-                     else "Connection to provider failed after")
-            self.agent._buffer_diagnostic_status(
-                f"❌ {_what} {max_retries + 1} attempts. The provider may be experiencing issues — try again in a moment.")
+            if _is_stream_parse_err or _is_empty_stream:
+                _what = ("Provider returned malformed streaming data after" if _is_stream_parse_err
+                         else "Provider returned an empty response stream after")
+                self.agent._buffer_diagnostic_status(
+                    f"❌ {_what} {max_retries + 1} attempts. The provider may be experiencing issues — try again in a moment.")
+            else:
+                from agent.stream_diag import buffer_connect_exhausted_notice
+                buffer_connect_exhausted_notice(self.agent, e, attempts=max_retries + 1, base_url=self.agent.base_url)
         else:
             self._maybe_disable_streaming(e)
             logger.exception("Streaming failed before delivery: %s", e)
diff --git a/agent/codex_runtime.py b/agent/codex_runtime.py
index 09009f5996..3e37bf39f2 100644
--- a/agent/codex_runtime.py
+++ b/agent/codex_runtime.py
@@ -17,6 +17,7 @@ from typing import Any, Callable, Dict, List
 from agent.stream_single_writer import claim_stream_writer, stream_writer_is_current
 from agent.transports.hermes_tools_mcp_server import HERMES_TOOLS_MCP_SERVER_NAME
 from agent.sdk_transform_bypass import bypass_sdk_request_transform
+from agent.stream_diag import buffer_connect_exhausted_notice
 from agent.usage_anchor import set_usage_anchor
 
 logger = logging.getLogger(__name__)
@@ -1040,6 +1041,11 @@ def run_codex_stream(agent, api_kwargs: dict, client: Any = None, on_first_delta
                        "exception_chain=%s model=%s attempt=%s", "unknown" if request_body_bytes is None else request_body_bytes,
                        str(writer_token["value"] is not None).lower(), exception_chain, getattr(agent, "model", "unknown"),
                        f"{attempt + 1}/{max_stream_retries + 1}")
+        if writer_token["value"] is None:
+            # No stream ever opened: the user gets one line naming host/attempts/size (#97548).
+            buffer_connect_exhausted_notice(
+                agent, exc, attempts=attempt + 1,
+                base_url=getattr(active_client, "base_url", None) or getattr(agent, "base_url", ""))
 
     def _codex_stream_created(_raw_stream: Any) -> None:
         # Claim the delta sink for THIS attempt; a newer attempt supersedes this token.
diff --git a/agent/stream_diag.py b/agent/stream_diag.py
index 3bc1d56b53..cb1b42e25c 100644
--- a/agent/stream_diag.py
+++ b/agent/stream_diag.py
@@ -155,8 +155,67 @@ def emit_stream_drop(
         pass
 
 
+# Above this size a refused/reset connect is as likely a body-size limit on the endpoint or a proxy
+# in front of it as an outage, so the notice says so (#97548: an ~829 KB request failed twice
+# before the stream opened while short chats went through).
+LARGE_REQUEST_HINT_BYTES = 256 * 1024
+
+
+def _failed_request(error: BaseException) -> Any:
+    """The buffered ``httpx.Request`` carried by the exception chain (SDK wrapper or httpx error), else None."""
+    link: Optional[BaseException] = error
+    for _ in range(8):
+        if link is None:
+            return None
+        try:
+            request = getattr(link, "request", None)
+        except RuntimeError:  # httpx raises when the error was built without a request
+            request = None
+        if request is not None:
+            return request
+        link = link.__cause__ or link.__context__
+    return None
+
+
+def _request_body_bytes(request: Any) -> Optional[int]:
+    content = getattr(request, "content", None)
+    if isinstance(content, str):
+        return len(content.encode("utf-8"))
+    if isinstance(content, (bytes, bytearray, memoryview)):
+        return len(content)
+    return None
+
+
+def connect_exhausted_notice(error: BaseException, *, attempts: int, base_url: Any) -> str:
+    """The one user-facing line for \"no stream event ever arrived and the connect retries are spent\":
+    names the host, the attempt count and the serialized request size so a body-size limit is
+    distinguishable from an outage without reading agent.log."""
+    from urllib.parse import urlparse
+    request = _failed_request(error)
+    host = urlparse(str(getattr(request, "url", None) or base_url or "")).hostname or "the endpoint"
+    size = _request_body_bytes(request)
+    line = f"❌ Could not open a stream to {host} after {attempts} attempt{'s' if attempts != 1 else ''}"
+    if size is None:
+        return line + "; the endpoint looks unreachable — try again in a moment."
+    line += f" (request {max(1, round(size / 1024))} KB)"
+    if size >= LARGE_REQUEST_HINT_BYTES:
+        return line + "; the endpoint or a proxy in front of it may reject requests this large."
+    return line + "; the endpoint looks unreachable — try again in a moment."
+
+
+def buffer_connect_exhausted_notice(agent: Any, error: BaseException, *, attempts: int, base_url: Any) -> None:
+    """Buffer :func:`connect_exhausted_notice` once per turn: the outer retry/fallback loop re-enters the
+    stream call several times, and every pass exhausting the same budget must not add another copy."""
+    text = connect_exhausted_notice(error, attempts=attempts, base_url=base_url)
+    if any(str(msg) == text for _kind, msg in getattr(agent, "_retry_status_buffer", None) or ()):
+        return
+    agent._buffer_diagnostic_status(text)
+
+
 __all__ = [
     "STREAM_DIAG_HEADERS",
+    "connect_exhausted_notice",
+    "buffer_connect_exhausted_notice",
     "stream_diag_init",
     "stream_diag_capture_response",
     "flatten_exception_chain",
diff --git a/tests/agent/test_codex_request_transport_diagnostics.py b/tests/agent/test_codex_request_transport_diagnostics.py
index fa1e272d8e..c1226af3b2 100644
--- a/tests/agent/test_codex_request_transport_diagnostics.py
+++ b/tests/agent/test_codex_request_transport_diagnostics.py
@@ -52,6 +52,7 @@ def test_transport_failure_logs_exact_request_bytes_and_class_chain(caplog):
         provider="openai-codex",
         session_id="",
         _client_log_context=lambda: "",
+        _buffer_diagnostic_status=lambda message: None,
     )
 
     with caplog.at_level(logging.WARNING, logger="agent.codex_runtime"):
diff --git a/tests/agent/test_run_agent_codex_responses.py b/tests/agent/test_run_agent_codex_responses.py
index 7de957f44b..f9b635a658 100644
--- a/tests/agent/test_run_agent_codex_responses.py
+++ b/tests/agent/test_run_agent_codex_responses.py
@@ -2958,6 +2958,31 @@ def test_run_codex_stream_prestream_retry_exhaustion_logs_telemetry(
     assert "attempt=2/2" in message
 
 
+def test_run_codex_stream_prestream_exhaustion_buffers_one_user_line_with_host_attempts_size(monkeypatch):
+    """#97548: when the pre-stream connect retries are spent the user gets ONE line naming the
+    endpoint host, the attempt count and the serialized request size (agent.log was the only place
+    those lived), and re-entering the stream call from the outer retry loop does not add a copy."""
+    import httpx
+    from openai import APIConnectionError
+
+    agent = _build_agent(monkeypatch)
+    body = b'{"model":"gpt-5-codex","input":"' + b"x" * (829 * 1024) + b'"}'
+    request = httpx.Request("POST", "https://api.example.com/backend-api/codex/responses", content=body)
+    agent.client = SimpleNamespace(responses=SimpleNamespace(
+        create=lambda **kwargs: _raise_prestream_transport_error(request)))
+
+    for _outer_retry in range(2):
+        with pytest.raises(APIConnectionError):
+            agent._run_codex_stream(_codex_request_kwargs())
+
+    lines = [str(msg) for _kind, msg in agent._retry_status_buffer]
+    assert len(lines) == 1, lines
+    assert "api.example.com" in lines[0]
+    assert "after 2 attempts" in lines[0]
+    assert f"request {round(len(body) / 1024)} KB" in lines[0]
+    assert "reject requests this large" in lines[0]
+
+
 def _codex_truncated_tool_call_response():
     """``status=incomplete`` (max_output_tokens) whose function_call item was cut mid-arguments
     and settled as ``completed`` — the self-hosted /v1/responses shape from #91770."""
diff --git a/website/docs/reference/faq.md b/website/docs/reference/faq.md
index 83c9c1a555..9d96c5474d 100644
--- a/website/docs/reference/faq.md
+++ b/website/docs/reference/faq.md
@@ -230,6 +230,12 @@ To isolate the source:
 
 See [Security](../user-guide/security.md) for Hermes' documented execution controls and [Providers](../integrations/providers.md) for provider configuration.
 
+#### "Could not open a stream to `<host>` after N attempts (request X KB)"
+
+**Meaning:** every connect attempt to that endpoint failed before a single stream event arrived, so nothing was billed; the normal retry/fallback chain still runs afterwards. The line names the host actually contacted, how many attempts were made, and the serialized request size — the three things that separate an outage from a request-size limit.
+
+**Solution:** if the request is large (hundreds of KB — long coding sessions reach this once the context grows) and short new chats work, the endpoint or a proxy in front of it is likely rejecting bodies that size: raise its body limit, or run `/compress` to shrink the context. If the request is small, the endpoint is unreachable — check the `base_url`, then retry with `/retry`. `logs/agent.log` records the exception chain for each attempt.
+
 #### `/model` only shows one provider / can't switch providers
 
 **Cause:** `/model` (inside a chat session) can only switch between providers you've **already configured**. If you've only set up OpenRouter, that's all `/model` will show.