fix(github): resolve follow-up review API issues

- Fix gh_client.py: use query string syntax for `since` parameter instead
  of `-f` flag which sends POST body fields, causing GitHub API errors
- Fix followup_reviewer.py: use raw Anthropic client for message API calls
  instead of ClaudeSDKClient which is for agent sessions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/backend/runners/github/gh_client.py

@@ -665,8 +665,9 @@ class GHClient:
             - issue_comments: General PR discussion comments
         """
         # Fetch inline review comments
-        review_endpoint = f"repos/{{owner}}/{{repo}}/pulls/{pr_number}/comments"
-        review_args = ["api", review_endpoint, "-f", f"since={since_timestamp}"]
+        # Use query string syntax - the -f flag sends POST body fields, not query params
+        review_endpoint = f"repos/{{owner}}/{{repo}}/pulls/{pr_number}/comments?since={since_timestamp}"
+        review_args = ["api", review_endpoint]
         review_result = await self.run(review_args, raise_on_error=False)
 
         review_comments = []
@@ -677,8 +678,9 @@ class GHClient:
                 logger.warning(f"Failed to parse review comments for PR #{pr_number}")
 
         # Fetch general issue comments
-        issue_endpoint = f"repos/{{owner}}/{{repo}}/issues/{pr_number}/comments"
-        issue_args = ["api", issue_endpoint, "-f", f"since={since_timestamp}"]
+        # Use query string syntax - the -f flag sends POST body fields, not query params
+        issue_endpoint = f"repos/{{owner}}/{{repo}}/issues/{pr_number}/comments?since={since_timestamp}"
+        issue_args = ["api", issue_endpoint]
         issue_result = await self.run(issue_args, raise_on_error=False)
 
         issue_comments = []

apps/backend/runners/github/services/followup_reviewer.py

@@ -543,10 +543,9 @@ class FollowupReviewer:
         Returns parsed AI response with finding resolutions and new findings,
         or None if AI review fails.
         """
-        try:
-            from ...core.client import create_client
-        except ImportError:
-            from core.client import create_client
+        # Use raw Anthropic client for simple message API calls
+        # (ClaudeSDKClient is for agent sessions, not direct message calls)
+        import anthropic
 
         self._report_progress(
             "analyzing", 65, "Running AI-powered review...", context.pr_number
@@ -624,16 +623,13 @@ Please analyze this follow-up review context and provide your response in the JS
 """
 
         try:
-            # Create client and run the review
-            client = create_client(
-                project_dir=self.project_dir,
-                spec_dir=self.github_dir,
-                model=self.config.model or "claude-sonnet-4-5-20250929",
-                agent_type="qa_reviewer",
-            )
+            # Create Anthropic client for simple message API call
+            # Note: For agent sessions with tools, use ClaudeSDKClient instead
+            client = anthropic.AsyncAnthropic()
+            model = self.config.model or "claude-sonnet-4-5-20250929"
 
             response = await client.messages.create(
-                model=self.config.model or "claude-sonnet-4-5-20250929",
+                model=model,
                 max_tokens=4096,
                 messages=[{"role": "user", "content": user_message}],
             )