diff --git a/pr-triage/tests/test_e2e.py b/pr-triage/tests/test_e2e.py
index 95ea98f..244b5ef 100644
--- a/pr-triage/tests/test_e2e.py
+++ b/pr-triage/tests/test_e2e.py
@@ -25,6 +25,7 @@ def __init__(self):
         self.calls = []  # (method, path, body_dict_or_None)
         self.model_reply = None  # str content, or Exception subclass to raise, or dict for raw payload
         self.model_status = 200
+        self.model_mode = "json"  # json | redirect | html
         self.files = [{"filename": "docs/architecture.md", "status": "modified"}]
         self.diff = "--- a/docs/architecture.md\n+++ b/docs/architecture.md\n@@ -1 +1 @@\n-old\n+new\n"
         self.permission = "admin"
@@ -72,12 +73,25 @@ def _route(self, method):
 
         if path == "/v1/chat/completions":
             s.model_headers = {k.lower(): v for k, v in self.headers.items()}
+            if s.model_mode == "redirect":
+                self.send_response(302)
+                self.send_header("Location", f"http://127.0.0.1:{self.server.server_address[1]}/cdn-cgi/access/login/llm.ionite.io?kid=abc")
+                self.send_header("Content-Length", "0")
+                self.end_headers()
+                return
+            if s.model_mode == "html":
+                page = "<!DOCTYPE html><html><head><title>Sign in · Cloudflare Access</title></head><body>" + "login " * 40 + "</body></html>"
+                assert len(page) > 200  # the 120-char cap must be measurable
+                return self._send(200, page, "text/html; charset=utf-8")
             if s.model_status != 200:
                 return self._send(s.model_status, {"error": "nope"})
             if isinstance(s.model_reply, dict):
                 return self._send(200, s.model_reply)
             return self._send(200, {"choices": [{"message": {"role": "assistant", "content": s.model_reply}}]})
 
+        if path.startswith("/cdn-cgi/access/login"):
+            return self._send(200, "<html>followed the redirect</html>", "text/html")
+
         prefix = "/github/repos/LykosAI/Test"
         if not path.startswith(prefix):
             return self._send(404, {"message": "unknown"})
@@ -317,6 +331,82 @@ def test_empty_content_with_only_reasoning_is_the_offline_path(self):
         self.assertEqual(self.calls("POST", "/pulls/7/reviews"), [])
         self.assertEqual(len(self.calls("POST", "/issues/7/comments")), 1)
 
+    def test_access_redirect_is_reported_as_a_302_and_never_followed(self):
+        self.state.model_mode = "redirect"
+        result = self.run_script()
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(self.calls("POST", "/pulls/7/reviews"), [])
+        self.assertIn("could not reach my model", self.calls("POST", "/issues/7/comments")[0][2]["body"])
+        self.assertEqual(len(self.calls("POST", "/v1/chat/completions")), 1)
+        self.assertEqual([c for c in self.state.calls if c[1].startswith("/cdn-cgi/")], [])
+        warning = [l for l in result.stdout.splitlines() if "::warning::Model unreachable" in l][0]
+        self.assertIn("ModelReplyError", warning)
+        self.assertIn("HTTP 302 redirect to 127.0.0.1", warning)
+        self.assertNotIn("kid=abc", warning)
+        for secret in ("cf-id-value", "cf-secret-value", "llm-key-value"):
+            self.assertNotIn(secret, result.stdout + result.stderr)
+
+    def test_html_200_is_reported_with_status_url_content_type_and_capped_body(self):
+        self.state.model_mode = "html"
+        result = self.run_script()
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(self.calls("POST", "/pulls/7/reviews"), [])
+        self.assertIn("could not reach my model", self.calls("POST", "/issues/7/comments")[0][2]["body"])
+        warning = [l for l in result.stdout.splitlines() if "::warning::Model unreachable" in l][0]
+        self.assertIn("non-JSON reply: HTTP 200 from http://127.0.0.1:", warning)
+        self.assertIn("/v1/chat/completions", warning)
+        self.assertIn("Content-Type text/html; charset=utf-8", warning)
+        self.assertIn("<!DOCTYPE html><html><head><title>Sign in", warning)
+        self.assertNotIn("</html>", warning)  # capped well before the end of the body
+        for secret in ("cf-id-value", "cf-secret-value", "llm-key-value"):
+            self.assertNotIn(secret, result.stdout + result.stderr)
+
+    def test_credential_presence_line_carries_booleans_and_lengths_only(self):
+        self.state.model_reply = '{"verdict": "human", "reason": "hm"}'
+        result = self.run_script()
+        line = [l for l in result.stdout.splitlines() if l.startswith("Model credentials in the environment:")][0]
+        self.assertIn("CF_ACCESS_CLIENT_ID present=True len=11", line)
+        self.assertIn("CF_ACCESS_CLIENT_SECRET present=True len=15", line)
+        self.assertIn("LLM_API_KEY present=True len=13", line)
+        for secret in ("cf-id-value", "cf-secret-value", "llm-key-value"):
+            self.assertNotIn(secret, line)
+
+    def test_missing_credentials_show_as_absent(self):
+        self.state.model_reply = '{"verdict": "human", "reason": "hm"}'
+        env = dict(
+            os.environ,
+            GITHUB_EVENT_PATH=self.event_path,
+            GITHUB_REPOSITORY="LykosAI/Test",
+            GITHUB_API_URL=f"http://127.0.0.1:{self.port}/github",
+            GITHUB_TOKEN="ghs_fake",
+            TRIAGE_MODEL="fake-model",
+            TRIAGE_ENDPOINT=f"http://127.0.0.1:{self.port}/v1",
+            CF_ACCESS_CLIENT_ID="",
+            PYTHONIOENCODING="utf-8",
+        )
+        env.pop("CF_ACCESS_CLIENT_SECRET", None)
+        env.pop("LLM_API_KEY", None)
+        result = subprocess.run([sys.executable, SCRIPT], env=env, capture_output=True, text=True, encoding="utf-8", timeout=60)
+        line = [l for l in result.stdout.splitlines() if l.startswith("Model credentials in the environment:")][0]
+        self.assertIn("CF_ACCESS_CLIENT_ID present=False len=0", line)
+        self.assertIn("CF_ACCESS_CLIENT_SECRET present=False len=0", line)
+        self.assertIn("LLM_API_KEY present=False len=0", line)
+
+    def test_ask_model_raises_a_diagnosable_error_on_redirect_and_html(self):
+        sys.path.insert(0, os.path.join(HERE, ".."))
+        import triage
+
+        endpoint = f"http://127.0.0.1:{self.port}/v1"
+        self.state.model_mode = "redirect"
+        with self.assertRaises(triage.ModelReplyError) as ctx:
+            triage.ask_model(endpoint, "m", "k", "i", "s", "sys", "user")
+        self.assertIn("HTTP 302 redirect to 127.0.0.1", str(ctx.exception))
+        self.state.model_mode = "html"
+        with self.assertRaises(triage.ModelReplyError) as ctx:
+            triage.ask_model(endpoint, "m", "k", "i", "s", "sys", "user")
+        self.assertIn("non-JSON reply: HTTP 200", str(ctx.exception))
+        self.assertIn("text/html", str(ctx.exception))
+
     def test_github_outage_exits_zero(self):
         self.state.model_reply = '{"verdict": "approve", "reason": "ok"}'
         env_override = f"http://127.0.0.1:{self.port}/nowhere"
diff --git a/pr-triage/triage.py b/pr-triage/triage.py
index 5ea782f..404ae05 100644
--- a/pr-triage/triage.py
+++ b/pr-triage/triage.py
@@ -28,6 +28,7 @@
 import re
 import sys
 import urllib.error
+import urllib.parse
 import urllib.request
 from dataclasses import dataclass, field
 from typing import Any
@@ -315,10 +316,32 @@ def render_comment_body(
 
 
 class HttpError(Exception):
-    def __init__(self, status: int, body: str):
+    def __init__(self, status: int, body: str, headers: dict[str, str] | None = None):
         super().__init__(f"HTTP {status}: {body[:300]}")
         self.status = status
         self.body = body
+        self.headers = headers or {}
+
+
+class ModelReplyError(Exception):
+    """The model endpoint answered with something other than a chat completion.
+
+    The message is safe to log: status, final URL, content type, redirect host and a
+    capped body prefix; never a request header value.
+    """
+
+
+class _NoRedirect(urllib.request.HTTPRedirectHandler):
+    def redirect_request(self, req, fp, code, msg, headers, newurl):
+        return None
+
+
+@dataclass(frozen=True)
+class HttpResponse:
+    status: int
+    body: str
+    headers: dict[str, str]
+    url: str
 
 
 def http(
@@ -327,18 +350,20 @@ def http(
     headers: dict[str, str],
     body: Any = None,
     timeout: float = GITHUB_TIMEOUT_SECONDS,
-) -> tuple[int, str, dict[str, str]]:
+    follow_redirects: bool = True,
+) -> HttpResponse:
     data = None
     req_headers = dict(headers)
     if body is not None:
         data = json.dumps(body).encode("utf-8")
         req_headers["Content-Type"] = "application/json"
     req = urllib.request.Request(url, data=data, method=method, headers=req_headers)
+    opener = urllib.request.build_opener() if follow_redirects else urllib.request.build_opener(_NoRedirect())
     try:
-        with urllib.request.urlopen(req, timeout=timeout) as resp:
-            return resp.status, resp.read().decode("utf-8", "replace"), dict(resp.headers)
+        with opener.open(req, timeout=timeout) as resp:
+            return HttpResponse(resp.status, resp.read().decode("utf-8", "replace"), dict(resp.headers), resp.geturl())
     except urllib.error.HTTPError as e:
-        raise HttpError(e.code, e.read().decode("utf-8", "replace")) from e
+        raise HttpError(e.code, e.read().decode("utf-8", "replace"), dict(e.headers)) from e
 
 
 class GitHub:
@@ -356,8 +381,7 @@ def _url(self, path: str) -> str:
         return f"{self.api_url}/repos/{self.repo}{path}"
 
     def get_json(self, path: str) -> Any:
-        _, text, _ = http("GET", self._url(path), self.headers)
-        return json.loads(text)
+        return json.loads(http("GET", self._url(path), self.headers).body)
 
     def get_paginated(self, path: str) -> list[Any]:
         items: list[Any] = []
@@ -372,8 +396,7 @@ def get_paginated(self, path: str) -> list[Any]:
 
     def get_diff(self, number: int) -> str:
         headers = dict(self.headers, Accept="application/vnd.github.diff")
-        _, text, _ = http("GET", self._url(f"/pulls/{number}"), headers)
-        return text
+        return http("GET", self._url(f"/pulls/{number}"), headers).body
 
     def author_permission(self, login: str) -> str | None:
         try:
@@ -433,6 +456,17 @@ def ask_model(
     system_prompt: str,
     user_content: str,
 ) -> str | None:
+    log(
+        "Model credentials in the environment: "
+        + ", ".join(
+            f"{name} present={bool(value)} len={len(value)}"
+            for name, value in (
+                ("CF_ACCESS_CLIENT_ID", cf_id),
+                ("CF_ACCESS_CLIENT_SECRET", cf_secret),
+                ("LLM_API_KEY", api_key),
+            )
+        )
+    )
     headers = {
         "Authorization": f"Bearer {api_key}",
         "CF-Access-Client-Id": cf_id,
@@ -449,14 +483,30 @@ def ask_model(
         "max_tokens": 2500,
         "reasoning_effort": "low",
     }
-    _, text, _ = http(
-        "POST",
-        endpoint.rstrip("/") + "/chat/completions",
-        headers,
-        payload,
-        timeout=MODEL_TIMEOUT_SECONDS,
-    )
-    data = json.loads(text)
+    try:
+        resp = http(
+            "POST",
+            endpoint.rstrip("/") + "/chat/completions",
+            headers,
+            payload,
+            timeout=MODEL_TIMEOUT_SECONDS,
+            follow_redirects=False,
+        )
+    except HttpError as e:
+        if 300 <= e.status < 400:
+            location = e.headers.get("Location") or e.headers.get("location") or ""
+            host = urllib.parse.urlsplit(location).netloc or "(no Location header)"
+            raise ModelReplyError(f"HTTP {e.status} redirect to {host}; an Access login page means the service token was not accepted") from e
+        raise
+    content_type = resp.headers.get("Content-Type") or resp.headers.get("content-type") or "(none)"
+    try:
+        data = json.loads(resp.body)
+    except json.JSONDecodeError as e:
+        raise ModelReplyError(
+            f"non-JSON reply: HTTP {resp.status} from {resp.url}, Content-Type {content_type}, body starts {resp.body[:120]!r}"
+        ) from e
+    if not isinstance(data, dict):
+        raise ModelReplyError(f"JSON reply is not an object: HTTP {resp.status} from {resp.url}, body starts {resp.body[:120]!r}")
     choices = data.get("choices") or []
     if not choices:
         return None