idempotent comment updates for re-reviews

src/arbiter/integrations/__init__.py

@@ -1,6 +1,7 @@
 """Platform integration clients for GitHub and GitLab."""
 
 from arbiter.integrations.base import (
+    Comment,
     CommitStatus,
     Platform,
     PlatformClient,
@@ -13,12 +14,18 @@ from arbiter.integrations.exceptions import (
     PlatformError,
     RateLimitError,
 )
-from arbiter.integrations.formatters import ReviewCommentFormatter
+from arbiter.integrations.formatters import (
+    ARBITER_MARKER,
+    ReviewCommentFormatter,
+    has_arbiter_marker,
+)
 from arbiter.integrations.github import GitHubClient
 from arbiter.integrations.gitlab import GitLabClient
 
 __all__ = [
+    "ARBITER_MARKER",
     "AuthenticationError",
+    "Comment",
     "CommitStatus",
     "GitHubClient",
     "GitLabClient",
@@ -30,4 +37,5 @@ __all__ = [
     "PullRequestInfo",
     "RateLimitError",
     "ReviewCommentFormatter",
+    "has_arbiter_marker",
 ]