Fix code review issues: add refs/heads prefix and null checks

Co-authored-by: Malcolmnixon <1863707+Malcolmnixon@users.noreply.github.com>

Author: Copilot

src/DemaConsulting.BuildMark/RepoConnectors/GitHub/GitHubGraphQLClient.cs

@@ -93,7 +93,7 @@ internal GitHubGraphQLClient(HttpClient httpClient, string? graphqlEndpoint = nu
     /// </summary>
     /// <param name="owner">Repository owner.</param>
     /// <param name="repo">Repository name.</param>
-    /// <param name="branch">Branch name.</param>
+    /// <param name="branch">Branch name (e.g., 'main'). Will be automatically converted to fully qualified ref name.</param>
     /// <returns>List of commit SHAs on the branch.</returns>
     public async Task<List<string>> GetCommitsAsync(
         string owner,
@@ -106,6 +106,9 @@ public async Task<List<string>> GetCommitsAsync(
             string? afterCursor = null;
             bool hasNextPage;
 
+            // Convert branch name to fully qualified ref name if needed
+            var qualifiedBranch = branch.StartsWith("refs/") ? branch : $"refs/heads/{branch}";
+
             // Paginate through all commits on the branch
             do
             {
@@ -136,7 +139,7 @@ ... on Commit {
                     {
                         owner,
                         repo,
-                        branch,
+                        branch = qualifiedBranch,
                         after = afterCursor
                     }
                 };

test/DemaConsulting.BuildMark.Tests/RepoConnectors/GitHub/GitHubGraphQLClientTests.cs

@@ -350,7 +350,9 @@ protected override async Task<HttpResponseMessage> SendAsync(
             CancellationToken cancellationToken)
         {
             // Read request body to determine which page to return
-            var requestBody = await request.Content!.ReadAsStringAsync(cancellationToken);
+            var requestBody = request.Content != null
+                ? await request.Content.ReadAsStringAsync(cancellationToken)
+                : string.Empty;
 
             string responseContent;
             if (_requestCount == 0 || !requestBody.Contains("\"after\""))
@@ -699,7 +701,9 @@ protected override async Task<HttpResponseMessage> SendAsync(
             CancellationToken cancellationToken)
         {
             // Read request body to determine which page to return
-            var requestBody = await request.Content!.ReadAsStringAsync(cancellationToken);
+            var requestBody = request.Content != null
+                ? await request.Content.ReadAsStringAsync(cancellationToken)
+                : string.Empty;
 
             string responseContent;
             if (_requestCount == 0 || !requestBody.Contains("\"after\""))