diff --git a/api/tests/unit_tests/models/test_model.py b/api/tests/unit_tests/models/test_model.py
index bb3206713d7..68eacab6cd6 100644
--- a/api/tests/unit_tests/models/test_model.py
+++ b/api/tests/unit_tests/models/test_model.py
@@ -138,3 +138,54 @@ def test_message_inputs_resolve_file_tenant_with_caller_session() -> None:
 
     assert inputs["file"] == "tenant-1"
     session.scalar.assert_called_once()
+
+
+def test_file_url_bare_url_re_signed():
+    """#40788: bare tool file URL (no markdown wrapping) must be re-signed.
+
+    Bare URLs are produced by the agent runtime when the model returns a
+    non-linkified file reference. The previous regex only matched
+    [text](url) markdown form, so the bare URL kept INTERNAL_FILES_URL.
+    """
+    upload_id = "bare-1"
+    url = f"/files/{upload_id}/file-preview?timestamp=1&nonce=2&sign=3"
+    msg = Message(answer=url)  # bare, no markdown wrapping
+
+    out = msg.re_sign_file_url_answer
+    assert f"https://signed.example/{upload_id}" in out
+    assert url not in out
+
+
+def test_file_url_backticked_url_re_signed():
+    """#40788: backticked tool file URL must be re-signed.
+
+    Backticks are used by the runtime to quote file references inline.
+    The previous regex only matched [text](url), so backticked URLs
+    stayed on INTERNAL_FILES_URL.
+    """
+    upload_id = "tick-2"
+    url = f"/files/{upload_id}/file-preview?timestamp=10&nonce=20&sign=30"
+    msg = Message(answer=f"see `{url}` for details")
+
+    out = msg.re_sign_file_url_answer
+    assert f"https://signed.example/{upload_id}" in out
+    assert url not in out
+
+
+def test_file_url_mixed_formats_all_re_signed():
+    """#40788: all three URL shapes in the same answer are re-signed.
+
+    Sanity check that the three patterns cooperate — bare, backticked,
+    and markdown — without double-signing or skipping any.
+    """
+    upload_ids = ["mix-a", "mix-b", "mix-c"]
+    bare = f"/files/{upload_ids[0]}/file-preview?timestamp=1&nonce=2&sign=3"
+    tick = f"/files/{upload_ids[1]}/file-preview?timestamp=10&nonce=20&sign=30"
+    md = f"/files/{upload_ids[2]}/file-preview?timestamp=100&nonce=200&sign=300"
+    msg = Message(answer=f"raw {bare} ` {tick} ` and [file]({md})")
+
+    out = msg.re_sign_file_url_answer
+    for uid in upload_ids:
+        assert f"https://signed.example/{uid}" in out
+    for url in (bare, tick, md):
+        assert url not in out