fix: guard PR/issue comment listing against non-list API payloads (Closes #485)

_list_pr_lease_comments and gitea_list_issue_comments now fail safe to an
empty list when the comments API returns a non-list payload (e.g. an error
object), preventing KeyError: slice on the lease and listing paths.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

gitea_mcp_server.py

@@ -2515,7 +2515,12 @@ def _list_pr_lease_comments(
     h, o, r = _resolve(remote, host, org, repo)
     auth = _auth(h)
     api = f"{repo_api_url(h, o, r)}/issues/{pr_number}/comments"
-    comments = api_request("GET", api, auth) or []
+    comments = api_request("GET", api, auth)
+    # Fail safe to no lease comments when the API returns a non-list payload
+    # (e.g. an error object such as an HTTP 401 body): lease state can only be
+    # proven from real comment entries, never inferred from an error shape (#485).
+    if not isinstance(comments, list):
+        return []
     return list(comments[:limit])
 
 
@@ -5119,7 +5124,12 @@ def gitea_list_issue_comments(
     h, o, r = _resolve(remote, host, org, repo)
     auth = _auth(h)
     api = f"{repo_api_url(h, o, r)}/issues/{issue_number}/comments"
-    comments = api_request("GET", api, auth) or []
+    comments = api_request("GET", api, auth)
+    # Fail safe to no comments when the API returns a non-list payload (e.g. an
+    # error object such as an HTTP 401 body) so listing never crashes on a
+    # malformed response (#485).
+    if not isinstance(comments, list):
+        comments = []
     reveal = _reveal_endpoints()
     out = []
     for c in comments[:limit]:

tests/test_pr_lease_comments_non_list_guard.py

@@ -0,0 +1,76 @@
+"""Regression tests for non-list API payloads on PR/issue comment listing (#485)."""
+import os
+import sys
+import unittest
+from unittest.mock import patch
+
+sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
+
+from mcp_server import (  # noqa: E402
+    _list_pr_lease_comments,
+    gitea_list_issue_comments,
+)
+
+FAKE_AUTH = "Basic dGVzdDp0ZXN0"
+AUTHOR_ENV = {
+    "GITEA_PROFILE_NAME": "gitea-author",
+    "GITEA_ALLOWED_OPERATIONS": "gitea.read,gitea.issue.comment",
+}
+
+
+class TestPrLeaseCommentsNonListGuard(unittest.TestCase):
+    @patch("mcp_server.api_request")
+    @patch("mcp_server.get_auth_header", return_value=FAKE_AUTH)
+    def test_list_pr_lease_comments_non_list_payload_returns_empty(self, _auth, mock_api):
+        mock_api.return_value = {"message": "Unauthorized"}
+        result = _list_pr_lease_comments(
+            12, remote="prgs", host=None, org=None, repo=None)
+        self.assertEqual(result, [])
+
+    @patch("mcp_server.api_request")
+    @patch("mcp_server.get_auth_header", return_value=FAKE_AUTH)
+    def test_list_pr_lease_comments_none_returns_empty(self, _auth, mock_api):
+        mock_api.return_value = None
+        result = _list_pr_lease_comments(
+            12, remote="prgs", host=None, org=None, repo=None)
+        self.assertEqual(result, [])
+
+    @patch("mcp_server.api_request")
+    @patch("mcp_server.get_auth_header", return_value=FAKE_AUTH)
+    def test_list_pr_lease_comments_list_payload_unchanged(self, _auth, mock_api):
+        comment = {"id": 7, "body": "<!-- mcp-review-lease:v1 -->"}
+        mock_api.return_value = [comment]
+        result = _list_pr_lease_comments(
+            12, remote="prgs", host=None, org=None, repo=None, limit=5)
+        self.assertEqual(result, [comment])
+
+    @patch("mcp_server.api_request")
+    @patch("mcp_server.get_auth_header", return_value=FAKE_AUTH)
+    def test_list_issue_comments_non_list_payload_returns_empty(self, _auth, mock_api):
+        mock_api.return_value = {"message": "Unauthorized"}
+        with patch.dict(os.environ, AUTHOR_ENV, clear=True):
+            result = gitea_list_issue_comments(issue_number=9, remote="prgs")
+        self.assertTrue(result["success"])
+        self.assertEqual(result["comments"], [])
+
+    @patch("mcp_server.api_request")
+    @patch("mcp_server.get_auth_header", return_value=FAKE_AUTH)
+    def test_list_issue_comments_list_payload_unchanged(self, _auth, mock_api):
+        mock_api.return_value = [
+            {
+                "id": 101,
+                "user": {"login": "alice"},
+                "body": "hello",
+                "created_at": "2026-07-03T00:00:00Z",
+                "updated_at": "2026-07-03T01:00:00Z",
+            }
+        ]
+        with patch.dict(os.environ, AUTHOR_ENV, clear=True):
+            result = gitea_list_issue_comments(issue_number=9, remote="prgs")
+        self.assertTrue(result["success"])
+        self.assertEqual(len(result["comments"]), 1)
+        self.assertEqual(result["comments"][0]["author"], "alice")
+
+
+if __name__ == "__main__":
+    unittest.main()