refactor: validate reviewer-name early (fail fast before LLM call)

Moved validateReviewerName check to right after flag parsing. Previously
it ran after the LLM request completed — wasting an expensive API call
if the name was invalid.

Sonnet review finding #1.

cmd/review-bot/main.go

@@ -57,6 +57,11 @@ func main() {
 		os.Exit(1)
 	}
 
+	// Validate reviewer-name: only safe characters allowed in sentinel
+	if err := validateReviewerName(*reviewerName); err != nil {
+		log.Fatalf("%v", err)
+	}
+
 	// Parse repo owner/name
 	parts := strings.SplitN(*repo, "/", 2)
 	if len(parts) != 2 {
@@ -234,10 +239,6 @@ func main() {
 		return
 	}
 
-	// Validate reviewer-name: only safe characters allowed in sentinel
-	if err := validateReviewerName(*reviewerName); err != nil {
-		log.Fatalf("%v", err)
-	}
 	sentinel := fmt.Sprintf("<!-- review-bot:%s -->", *reviewerName)
 
 	log.Printf("Posting review (event=%s)...", event)

review/formatter_test.go

@@ -134,3 +134,28 @@ func TestFormatMarkdown_Sentinel(t *testing.T) {
 		t.Error("should not contain sentinel when reviewer name is empty")
 	}
 }
+
+func TestFormatMarkdown_RoleTitle(t *testing.T) {
+	result := &ReviewResult{
+		Verdict:        "APPROVE",
+		Summary:        "All good.",
+		Recommendation: "Merge it.",
+	}
+
+	// With reviewer name: should have title header
+	output := FormatMarkdown(result, "security")
+	if !strings.Contains(output, "# Security Review\n") {
+		t.Error("expected '# Security Review' header when reviewer name is set")
+	}
+
+	output2 := FormatMarkdown(result, "gpt")
+	if !strings.Contains(output2, "# Gpt Review\n") {
+		t.Error("expected '# Gpt Review' header")
+	}
+
+	// Without reviewer name: no title header
+	output3 := FormatMarkdown(result, "")
+	if strings.Contains(output3, "# ") && strings.Contains(output3, " Review\n") {
+		t.Error("should not contain role title header when reviewer name is empty")
+	}
+}