Fail closed on GitHub API errors during the sync workflow.

src/repo_sync/stack/gh_ops.py

@@ -291,18 +291,20 @@ def get_pr_for_commit(self, sha: str) -> PullRequest | None:
         lookup, avoiding false-positive text matches from gh pr list --search.
         Filters for merged PRs to avoid picking up open/closed PRs that happen
         to include the same commit.
+
+        Raises subprocess.CalledProcessError if the GitHub API call fails.
+        Callers in non-critical paths should catch this and degrade gracefully;
+        callers in safety-critical paths (e.g. loop detection) must let it
+        propagate to abort the workflow.
         """
-        try:
-            output = self._run(
-                [
-                    "api",
-                    f"repos/{self.repo}/commits/{sha}/pulls",
-                    "--jq",
-                    '[.[] | select(.merged_at != null)] | .[0]',
-                ],
-            )
-        except subprocess.CalledProcessError:
-            return None
+        output = self._run(
+            [
+                "api",
+                f"repos/{self.repo}/commits/{sha}/pulls",
+                "--jq",
+                '[.[] | select(.merged_at != null)] | .[0]',
+            ],
+        )
         if not output or output == "null":
             return None
         pr = json.loads(output)

src/repo_sync/stack/loop_detection.py

@@ -39,9 +39,15 @@ def is_sync_originated(
         return False
 
     # Check 2: was the commit merged from a repo-sync/ branch?
+    #
+    # get_pr_for_commit raises on API failure, which intentionally aborts
+    # the sync run.  We must not fail-open here: if we cannot verify the
+    # PR branch, we cannot safely determine whether this commit is
+    # sync-originated.
     pr = gh.get_pr_for_commit(commit_sha)
     if pr is None:
-        # No PR found -- this could be a direct push with a spoofed trailer.
+        # API succeeded but no merged PR was found — this could be a
+        # direct push with a spoofed trailer.
         return False
 
     if not is_sync_branch(pr.head_branch):

src/repo_sync/workflows/sync.py

@@ -12,6 +12,7 @@
 from __future__ import annotations
 
 import logging
+import subprocess
 from dataclasses import dataclass
 
 from repo_sync.stack.branches import check_idempotency
@@ -94,9 +95,17 @@ def enumerate_unsynced_commits(
     # Filter out sync-originated commits.
     result = []
     for sha in all_commits:
-        if is_sync_originated(source_git, source_gh, sha):
-            logger.info("Skipping sync-originated commit %s.", sha[:12])
-            continue
+        try:
+            if is_sync_originated(source_git, source_gh, sha):
+                logger.info("Skipping sync-originated commit %s.", sha[:12])
+                continue
+        except subprocess.CalledProcessError:
+            logger.error(
+                "GitHub API failure during loop detection for commit %s. "
+                "Aborting sync to avoid creating an infinite loop.",
+                sha[:12],
+            )
+            raise
         result.append(sha)
 
     return result
@@ -146,7 +155,15 @@ def build_public_to_private_description(
     direct pushes.
     """
     source_repo_name = source_repo.split("/")[-1]
-    source_pr = source_gh.get_pr_for_commit(source_sha)
+    try:
+        source_pr = source_gh.get_pr_for_commit(source_sha)
+    except subprocess.CalledProcessError:
+        logger.warning(
+            "GitHub API error looking up PR for commit %s; "
+            "falling back to commit-based description.",
+            source_sha[:12],
+        )
+        source_pr = None
 
     if source_pr is not None:
         return public_to_private_from_pr(
@@ -180,7 +197,15 @@ def determine_sync_reviewer(
     Tries the merger of the source PR first, then the commit author (via
     GitHub API), then the fallback team.
     """
-    source_pr = source_gh.get_pr_for_commit(source_sha)
+    try:
+        source_pr = source_gh.get_pr_for_commit(source_sha)
+    except subprocess.CalledProcessError:
+        logger.warning(
+            "GitHub API error looking up PR for commit %s; "
+            "falling back to commit author or team for reviewer.",
+            source_sha[:12],
+        )
+        source_pr = None
     pr_number = source_pr.number if source_pr else None
 
     # For direct pushes (no source PR), look up the commit author via the API.

tests/test_loop_detection.py

@@ -9,8 +9,11 @@
 
 from __future__ import annotations
 
+import subprocess
 from unittest.mock import MagicMock
 
+import pytest
+
 from repo_sync.stack.gh_ops import GhOps, PullRequest
 from repo_sync.stack.git_ops import GitOps
 from repo_sync.stack.loop_detection import is_sync_originated
@@ -99,6 +102,22 @@ def test_trailer_present_but_no_pr_found(self) -> None:
 
         assert is_sync_originated(git, gh, "directpush") is False
 
+    def test_api_failure_propagates_when_trailer_present(self) -> None:
+        """An API failure during PR lookup aborts rather than failing-open."""
+        git = MagicMock(spec=GitOps)
+        git.commit_message.return_value = (
+            "sync commit\n\n"
+            "Repo-Sync-Origin: warpdotdev/warp-internal@abc123"
+        )
+
+        gh = MagicMock(spec=GhOps)
+        gh.get_pr_for_commit.side_effect = subprocess.CalledProcessError(
+            1, ["gh", "api", "repos/org/repo/commits/abc123/pulls"]
+        )
+
+        with pytest.raises(subprocess.CalledProcessError):
+            is_sync_originated(git, gh, "abc123")
+
     def test_public_to_private_sync_branch_recognized(self) -> None:
         """Public-to-private sync branches are also recognized."""
         git = MagicMock(spec=GitOps)