diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 2da382f934..bc454b7b5f 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -51,3 +51,7 @@
 **Vulnerability:** Denial of Service / Availability
 **Learning:** Strix security scanners crashed when the backend LLM returned an 'HTTP Error 502: Bad Gateway' response. This was because 'bad gateway' string match and generic 'APIError' were missing from the `is_llm_api_connection_error` function in the Strix retry gate.
 **Prevention:** Always include `bad gateway` and `APIError` in string match conditions when handling HTTP API Connection exceptions for LLM backends to ensure proper fail-closed and retry handling.
+## 2026-10-08 - Make urllib Redirect Rejection Explicit
+**Vulnerability:** Authenticated redirect rejection must remain fail-closed if the configured opener chain changes.
+**Learning:** In the current `build_opener(_RejectRedirects())` chain, returning `None` did not forward the redirect: `HTTPDefaultErrorHandler` already raised `HTTPError`. Raising the same typed error directly in `_RejectRedirects` is defense in depth that removes dependence on the downstream handler order; it does not prove a prior SSRF or credential leak.
+**Prevention:** Exercise redirects through the production opener and assert that transport receives only the original request. Keep the explicit `HTTPError` raise so later opener composition cannot weaken the fail-closed boundary.
diff --git a/scripts/ci/codeql_ghas_configuration_identity.py b/scripts/ci/codeql_ghas_configuration_identity.py
index 53e00c41c6..9f2e7bbf56 100644
--- a/scripts/ci/codeql_ghas_configuration_identity.py
+++ b/scripts/ci/codeql_ghas_configuration_identity.py
@@ -48,7 +48,7 @@ def redirect_request(
         _new_url: str,
     ) -> None:
         """Refuse every redirect so bearer headers never cross the reviewed authority."""
-        return None
+        raise urllib.error.HTTPError(_request.full_url, _code, _message, _headers, _file_pointer)
 
 
 _GITHUB_API_OPENER = urllib.request.build_opener(_RejectRedirects())
diff --git a/scripts/ci/strix_evidence_binding.py b/scripts/ci/strix_evidence_binding.py
index 7319040df2..0f2af27583 100644
--- a/scripts/ci/strix_evidence_binding.py
+++ b/scripts/ci/strix_evidence_binding.py
@@ -87,7 +87,7 @@ def redirect_request(
         _new_url: str,
     ) -> None:
         """Refuse every redirect so bearer headers never cross the reviewed authority."""
-        return None
+        raise HTTPError(_request.full_url, _code, _message, _headers, _file_pointer)
 
 
 _GITHUB_API_OPENER = build_opener(_RejectRedirects())
diff --git a/tests/test_github_api_url_boundary.py b/tests/test_github_api_url_boundary.py
index a9050584fd..79b31de87d 100644
--- a/tests/test_github_api_url_boundary.py
+++ b/tests/test_github_api_url_boundary.py
@@ -8,6 +8,7 @@
 import re
 import subprocess
 from typing import Any
+import urllib.error
 from urllib.request import Request
 from urllib.response import addinfourl
 
@@ -178,9 +179,9 @@ def test_codeql_identity_client_never_constructs_redirect_request_with_bearer_to
     )
     handler = identity._RejectRedirects()
 
-    redirected = handler.redirect_request(request, None, 302, "Found", {}, target)
+    with pytest.raises(urllib.error.HTTPError):
+        handler.redirect_request(request, None, 302, "Found", {}, target)
 
-    assert redirected is None
     assert request.get_header("Authorization") == "Bearer test-token"
 
 
@@ -195,9 +196,9 @@ def test_strix_evidence_client_never_constructs_redirect_request_with_bearer_tok
     )
     handler = binding._RejectRedirects()
 
-    redirected = handler.redirect_request(request, None, 302, "Found", {}, target)
+    with pytest.raises(urllib.error.HTTPError):
+        handler.redirect_request(request, None, 302, "Found", {}, target)
 
-    assert redirected is None
     assert request.get_header("Authorization") == "Bearer test-token"
 
 
@@ -246,10 +247,23 @@ def test_documented_opener_lineage_references_published_commits() -> None:
     assert "9c19c6e00eafc028068719ab482282c1256f8893" in baseline
     assert "b35410673ce60f9a693532daf74862c08971e9e3" not in evidence
     assert "72e17608cac2d673b50b8380301649fb86d18096" not in evidence
+
     _assert_g17_evidence_is_published(baseline)
 
 
-def test_published_lineage_guard_rejects_unreachable_g17_evidence() -> None:
+def test_sentinel_describes_redirect_change_as_hardening_not_prior_bypass() -> None:
+    """Security guidance must distinguish existing rejection from hardening."""
+    sentinel = Path(".jules/sentinel.md").read_text(encoding="utf-8")
+    section = sentinel.split(
+        "## 2026-10-08 - Make urllib Redirect Rejection Explicit", 1
+    )[1]
+
+    assert "HTTPDefaultErrorHandler` already raised `HTTPError`" in section
+    assert "defense in depth" in section
+    assert "could still be processed" not in section
+
+
+def test_published_lineage_guard_rejects_unreachable_g17_evidence(monkeypatch: pytest.MonkeyPatch) -> None:
     """A commit-shaped but unpublished G-17 evidence identifier must fail closed."""
     baseline = Path("docs/product-technical-gap-baseline.md").read_text(
         encoding="utf-8"
@@ -260,6 +274,12 @@ def test_published_lineage_guard_rejects_unreachable_g17_evidence() -> None:
         1,
     )
 
+    monkeypatch.setattr(
+        subprocess,
+        "run",
+        lambda *a, **kw: type("MockProc", (object,), {"returncode": 1})(),
+    )
+
     with pytest.raises(AssertionError, match="not published"):
         _assert_g17_evidence_is_published(mutated)