Back off when PR has too many commits

Skip commit iteration and fail all rules when the PR has more than
100 commits, as this likely indicates the PR targets the wrong branch.
Applied to both MergeCommitsCheck and JiraIssuesCheck.

Assisted-By: Claude Code <noreply@anthropic.com>

Author: yrodiere

src/main/java/org/hibernate/infra/bot/CheckPullRequestContributionRules.java

@@ -196,13 +196,25 @@ public void perform(PullRequestCheckRunContext context, PullRequestCheckRunOutpu
 	}
 
 	static class MergeCommitsCheck extends PullRequestCheck {
+		private static final int MAX_COMMITS = 100;
 
 		MergeCommitsCheck() {
 			super( "Contribution — Merge commits" );
 		}
 
 		@Override
 		public void perform(PullRequestCheckRunContext context, PullRequestCheckRunOutput output) throws IOException {
+			String mergeCommitRuleName = "The pull request should not contain merge commits";
+			String fixupSquashRuleName = "The pull request should not contain fixup! or squash! commits";
+
+			if ( context.pullRequest.getCommits() > MAX_COMMITS ) {
+				String tooManyCommits = "Too many commits (%d) to process; the pull request is probably targeting the wrong branch."
+						.formatted( context.pullRequest.getCommits() );
+				output.rule( mergeCommitRuleName ).failed( tooManyCommits );
+				output.rule( fixupSquashRuleName ).failed( tooManyCommits );
+				return;
+			}
+
 			List<String> mergeCommitShas = new ArrayList<>();
 			List<String> fixupSquashCommitShas = new ArrayList<>();
 			for ( GHPullRequestCommitDetail commitDetail : context.pullRequest.listCommits() ) {
@@ -215,8 +227,7 @@ public void perform(PullRequestCheckRunContext context, PullRequestCheckRunOutpu
 				}
 			}
 
-			PullRequestCheckRunRule mergeCommitRule = output.rule(
-					"The pull request should not contain merge commits" );
+			PullRequestCheckRunRule mergeCommitRule = output.rule( mergeCommitRuleName );
 			if ( mergeCommitShas.isEmpty() ) {
 				mergeCommitRule.passed();
 			}
@@ -232,8 +243,7 @@ public void perform(PullRequestCheckRunContext context, PullRequestCheckRunOutpu
 				);
 			}
 
-			PullRequestCheckRunRule fixupSquashRule = output.rule(
-					"The pull request should not contain fixup! or squash! commits" );
+			PullRequestCheckRunRule fixupSquashRule = output.rule( fixupSquashRuleName );
 			if ( fixupSquashCommitShas.isEmpty() ) {
 				fixupSquashRule.passed();
 			}
@@ -270,6 +280,16 @@ static class JiraIssuesCheck extends IgnorablePullRequestCheck {
 
 		@Override
 		public void doPerform(PullRequestCheckRunContext context, PullRequestCheckRunOutput output) throws IOException {
+			String commitRuleName = "All commit messages should start with a JIRA issue key matching pattern `"
+					+ issueKeyPattern + "`";
+
+			if ( context.pullRequest.getCommits() > MergeCommitsCheck.MAX_COMMITS ) {
+				output.rule( commitRuleName )
+						.failed( "Too many commits (%d) to process; the pull request is probably targeting the wrong branch."
+								.formatted( context.pullRequest.getCommits() ) );
+				return;
+			}
+
 			String title = context.pullRequest.getTitle();
 			String body = context.pullRequest.getBody();
 
@@ -287,9 +307,7 @@ public void doPerform(PullRequestCheckRunContext context, PullRequestCheckRunOut
 				}
 			}
 
-			PullRequestCheckRunRule commitRule =
-					output.rule( "All commit messages should start with a JIRA issue key matching pattern `"
-							+ issueKeyPattern + "`" );
+			PullRequestCheckRunRule commitRule = output.rule( commitRuleName );
 			if ( commitsWithMessageNotStartingWithIssueKey.isEmpty() ) {
 				commitRule.passed();
 			}