diff --git a/agent/conversation_loop.py b/agent/conversation_loop.py
index 8503a7f90f9..959a55dc0e9 100644
--- a/agent/conversation_loop.py
+++ b/agent/conversation_loop.py
@@ -2259,6 +2259,15 @@ def run_conversation(
                     # "unknown variant `image_url`, expected `text`".
                     "unknown variant `image_url`, expected `text`",
                     "unknown variant image_url, expected text",
+                    # OpenRouter routes a request to upstream endpoints and,
+                    # when none of the candidate endpoints for the model accept
+                    # image input, returns HTTP 404 "No endpoints found that
+                    # support image input". Without this phrase the agent never
+                    # strips the images, the retry loop re-sends the same
+                    # rejected request until exhaustion, and the gateway leaves
+                    # every subsequent message queued behind the stuck turn —
+                    # the P1 in issue #21160. The 404 passes the 4xx gate below.
+                    "no endpoints found that support image input",
                 )
                 _err_lower = _err_body.lower()
                 _looks_like_image_rejection = any(
diff --git a/tests/run_agent/test_image_rejection_fallback.py b/tests/run_agent/test_image_rejection_fallback.py
index d1d6c7ff028..de960096eb0 100644
--- a/tests/run_agent/test_image_rejection_fallback.py
+++ b/tests/run_agent/test_image_rejection_fallback.py
@@ -195,6 +195,7 @@ class TestImageRejectionPhraseIsolation:
         "does not support vision",
         "model does not support image",
         "image_url'. expected",
+        "no endpoints found that support image input",
     )
 
     def _matches(self, body: str) -> bool:
@@ -244,10 +245,28 @@ class TestImageRejectionPhraseIsolation:
             # match the agent cascaded into compression / context-too-large
             # recovery instead of just stripping the images.
             "Invalid 'input[56].content[1].image_url'. Expected a valid URL, but got a value with an invalid format.",
+            # OpenRouter 404 when no upstream endpoint for the model accepts
+            # image input — issue #21160. The exact wording from the report.
+            "HTTP 404: No endpoints found that support image input",
         ]
         for body in bodies:
             assert self._matches(body) is True, f"false negative on: {body}"
 
+    def test_openrouter_data_policy_no_endpoints_does_not_trip(self):
+        """OpenRouter has several 'no endpoints ...' 404 bodies. Only the
+        image-input one is an image rejection — the guardrail / data-policy
+        variants (agent/error_classifier.py) are about routing restrictions,
+        not vision, and must route to their own handler, not get their images
+        stripped.
+        """
+        bodies = [
+            "No endpoints available matching your guardrail restrictions",
+            "No endpoints available matching your data policy",
+            "No endpoints found matching your data policy",
+        ]
+        for body in bodies:
+            assert self._matches(body) is False, f"false positive on: {body}"
+
     def test_codex_data_url_rejection_does_not_false_match_other_url_errors(self):
         """The narrow 'image_url'. expected' phrase (keyed on the
         field-path apostrophe used in the Codex Responses error format)