fix(azure-devops): gate fallback returns False; treat fetch errors as fallback

- _can_run_incremental_review() now returns False (not True) when
  incremental.commits_range is None, satisfying compliance ID 6 and
  the test_can_run_returns_false_when_commits_range_none unit test.
- PRReviewer.run() distinguishes "gate disabled incremental" (fall
  through to full review) from "gate said skip" (return early), so
  the previous fallback log line now produces an actual full review.
- _get_incremental_commits() tracks had_errors so that transient Azure
  get_changes failures disable incremental and fall back to a full
  review instead of being silently skipped as "no new files".

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: agonzales-ipcoop

pr_agent/git_providers/azuredevops_provider.py

@@ -216,6 +216,7 @@ def _get_incremental_commits(self):
 
         self.incremental.commits_range = self._get_commit_range()
         candidate_paths = []
+        had_errors = False
         for commit in self.incremental.commits_range:
             if len(commit.parents) > 1:
                 get_logger().info(f"Skipping merge commit {commit.sha}")
@@ -227,6 +228,7 @@ def _get_incremental_commits(self):
                     commit_id=commit.commit_id,
                 )
             except Exception as e:
+                had_errors = True
                 get_logger().warning(f"Failed to fetch changes for {commit.commit_id}: {e}")
                 continue
             for change in (getattr(changes_obj, "changes", None) or []):
@@ -247,6 +249,11 @@ def _get_incremental_commits(self):
             for path in filtered:
                 if is_valid_file(path):
                     self.unreviewed_files_set[path] = path
+        elif had_errors and self.incremental.commits_range:
+            get_logger().warning(
+                "Failed to fetch changes for incremental commits; falling back to full review."
+            )
+            self.incremental.is_incremental = False
 
     def _get_commit_range(self):
         last_review_time = _to_naive_utc(getattr(self.previous_review, "created_at", None))

pr_agent/tools/pr_reviewer.py

@@ -123,8 +123,11 @@ async def run(self) -> None:
                 get_logger().info(f"PR has no files: {self.pr_url}, skipping review")
                 return None
 
-            if self.incremental.is_incremental and not self._can_run_incremental_review():
-                return None
+            if self.incremental.is_incremental:
+                can_run = self._can_run_incremental_review()
+                # If the gate disabled incremental (e.g., commits_range is None), fall through to full review.
+                if not can_run and self.incremental.is_incremental:
+                    return None
 
             # if isinstance(self.args, list) and self.args and self.args[0] == 'auto_approve':
             #     get_logger().info(f'Auto approve flow PR: {self.pr_url} ...')
@@ -343,7 +346,7 @@ def _can_run_incremental_review(self) -> bool:
                 f"falling back to full review."
             )
             self.incremental.is_incremental = False
-            return True
+            return False
         # checking if there are enough commits to start the review
         num_new_commits = len(self.incremental.commits_range)
         num_commits_threshold = get_settings().pr_reviewer.minimal_commits_for_incremental_review