diff --git a/agent/auxiliary_client.py b/agent/auxiliary_client.py
index 479776428b..fd2f2d8122 100644
--- a/agent/auxiliary_client.py
+++ b/agent/auxiliary_client.py
@@ -899,6 +899,51 @@ def _current_custom_base_url() -> str:
     return custom_base or ""
 
 
+def _validate_proxy_env_urls() -> None:
+    """Fail fast with a clear error when proxy env vars have malformed URLs.
+
+    Common cause: shell config (e.g. .zshrc) with a typo like
+    ``export HTTP_PROXY=http://127.0.0.1:6153export NEXT_VAR=...``
+    which concatenates 'export' into the port number.  Without this
+    check the OpenAI/httpx client raises a cryptic ``Invalid port``
+    error that doesn't name the offending env var.
+    """
+    from urllib.parse import urlparse
+
+    for key in ("HTTPS_PROXY", "HTTP_PROXY", "ALL_PROXY",
+                "https_proxy", "http_proxy", "all_proxy"):
+        value = str(os.environ.get(key) or "").strip()
+        if not value:
+            continue
+        try:
+            parsed = urlparse(value)
+            if parsed.scheme:
+                _ = parsed.port          # raises ValueError for e.g. '6153export'
+        except ValueError as exc:
+            raise RuntimeError(
+                f"Malformed proxy environment variable {key}={value!r}. "
+                "Fix or unset your proxy settings and try again."
+            ) from exc
+
+
+def _validate_base_url(base_url: str) -> None:
+    """Reject obviously broken custom endpoint URLs before they reach httpx."""
+    from urllib.parse import urlparse
+
+    candidate = str(base_url or "").strip()
+    if not candidate or candidate.startswith("acp://"):
+        return
+    try:
+        parsed = urlparse(candidate)
+        if parsed.scheme in {"http", "https"}:
+            _ = parsed.port              # raises ValueError for malformed ports
+    except ValueError as exc:
+        raise RuntimeError(
+            f"Malformed custom endpoint URL: {candidate!r}. "
+            "Run `hermes setup` or `hermes model` and enter a valid http(s) base URL."
+        ) from exc
+
+
 def _try_custom_endpoint() -> Tuple[Optional[OpenAI], Optional[str]]:
     runtime = _resolve_custom_runtime()
     if len(runtime) == 2:
@@ -1299,6 +1344,7 @@ def resolve_provider_client(
     Returns:
         (client, resolved_model) or (None, None) if auth is unavailable.
     """
+    _validate_proxy_env_urls()
     # Normalise aliases
     provider = _normalize_aux_provider(provider)
 
diff --git a/run_agent.py b/run_agent.py
index 956a1e9638..3a017f739a 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -4206,6 +4206,9 @@ class AIAgent:
         return False
 
     def _create_openai_client(self, client_kwargs: dict, *, reason: str, shared: bool) -> Any:
+        from agent.auxiliary_client import _validate_base_url, _validate_proxy_env_urls
+        _validate_proxy_env_urls()
+        _validate_base_url(client_kwargs.get("base_url"))
         if self.provider == "copilot-acp" or str(client_kwargs.get("base_url", "")).startswith("acp://copilot"):
             from agent.copilot_acp_client import CopilotACPClient
 
diff --git a/scripts/release.py b/scripts/release.py
index b40fd7c239..4e5b193229 100755
--- a/scripts/release.py
+++ b/scripts/release.py
@@ -62,6 +62,7 @@ AUTHOR_MAP = {
     "258577966+voidborne-d@users.noreply.github.com": "voidborne-d",
     "70424851+insecurejezza@users.noreply.github.com": "insecurejezza",
     "259807879+Bartok9@users.noreply.github.com": "Bartok9",
+    "241404605+MestreY0d4-Uninter@users.noreply.github.com": "MestreY0d4-Uninter",
     "268667990+Roy-oss1@users.noreply.github.com": "Roy-oss1",
     "241404605+MestreY0d4-Uninter@users.noreply.github.com": "MestreY0d4-Uninter",
     # contributors (manual mapping from git names)
diff --git a/tests/agent/test_proxy_and_url_validation.py b/tests/agent/test_proxy_and_url_validation.py
new file mode 100644
index 0000000000..4fd6138a4d
--- /dev/null
+++ b/tests/agent/test_proxy_and_url_validation.py
@@ -0,0 +1,60 @@
+"""Tests for malformed proxy env var and base URL validation.
+
+Salvaged from PR #6403 by MestreY0d4-Uninter — validates that the agent
+surfaces clear errors instead of cryptic httpx ``Invalid port`` exceptions
+when proxy env vars or custom endpoint URLs are malformed.
+"""
+from __future__ import annotations
+
+import pytest
+
+from agent.auxiliary_client import _validate_base_url, _validate_proxy_env_urls
+
+
+# -- proxy env validation ------------------------------------------------
+
+
+def test_proxy_env_accepts_normal_values(monkeypatch):
+    monkeypatch.setenv("HTTP_PROXY", "http://127.0.0.1:6153")
+    monkeypatch.setenv("HTTPS_PROXY", "https://proxy.example.com:8443")
+    monkeypatch.setenv("ALL_PROXY", "socks5://127.0.0.1:1080")
+    _validate_proxy_env_urls()  # should not raise
+
+
+def test_proxy_env_accepts_empty(monkeypatch):
+    monkeypatch.delenv("HTTP_PROXY", raising=False)
+    monkeypatch.delenv("HTTPS_PROXY", raising=False)
+    monkeypatch.delenv("ALL_PROXY", raising=False)
+    monkeypatch.delenv("http_proxy", raising=False)
+    monkeypatch.delenv("https_proxy", raising=False)
+    monkeypatch.delenv("all_proxy", raising=False)
+    _validate_proxy_env_urls()  # should not raise
+
+
+@pytest.mark.parametrize("key", [
+    "HTTP_PROXY", "HTTPS_PROXY", "ALL_PROXY",
+    "http_proxy", "https_proxy", "all_proxy",
+])
+def test_proxy_env_rejects_malformed_port(monkeypatch, key):
+    monkeypatch.setenv(key, "http://127.0.0.1:6153export")
+    with pytest.raises(RuntimeError, match=rf"Malformed proxy environment variable {key}=.*6153export"):
+        _validate_proxy_env_urls()
+
+
+# -- base URL validation -------------------------------------------------
+
+
+@pytest.mark.parametrize("url", [
+    "https://api.example.com/v1",
+    "http://127.0.0.1:6153/v1",
+    "acp://copilot",
+    "",
+    None,
+])
+def test_base_url_accepts_valid(url):
+    _validate_base_url(url)  # should not raise
+
+
+def test_base_url_rejects_malformed_port():
+    with pytest.raises(RuntimeError, match="Malformed custom endpoint URL"):
+        _validate_base_url("http://127.0.0.1:6153export")