fix(scorer): make git-age tests month-start safe

internal/scorer/scorer_test.go

@@ -33,7 +33,7 @@ func setupGitRepo(t *testing.T, years, months int) (string, string) {
 		t.Fatalf("write file failed: %v", err)
 	}
 
-	commitDate := time.Now().AddDate(years, months, 0).Format(time.RFC3339)
+	commitDate := gitAgeBonusAnchor(years, months)
 	env := append(os.Environ(),
 		"GIT_AUTHOR_DATE="+commitDate,
 		"GIT_COMMITTER_DATE="+commitDate,
@@ -396,35 +396,42 @@ func TestFromL5Conversion(t *testing.T) {
 }
 
 // Git age bonus helper edge cases.
+// The anchor day exists in every month and is never later than today's day.
+func gitAgeBonusAnchor(years, months int) string {
+	now := time.Now()
+	safeDay := now.Day()
+	if safeDay > 28 {
+		safeDay = 28
+	}
+	anchor := time.Date(now.Year(), now.Month(), safeDay, 0, 0, 0, 0, now.Location())
+	return anchor.AddDate(years, months, 0).Format(time.RFC3339)
+}
+
 func TestGitAgeBonusExact24Months(t *testing.T) {
 	// Spec says >24 months for +10. Exactly 24 months qualifies for +5 (>12).
-	date := time.Now().AddDate(-2, 0, 0).Format(time.RFC3339)
-	bonus := gitAgeBonus(date)
+	bonus := gitAgeBonus(gitAgeBonusAnchor(-2, 0))
 	if bonus != 5 {
 		t.Errorf("expected bonus 5 for exactly 24 months, got %d", bonus)
 	}
 }
 
 func TestGitAgeBonusExact12Months(t *testing.T) {
 	// Spec says >12 months for +5. Exactly 12 months gets 0.
-	date := time.Now().AddDate(-1, 0, 0).Format(time.RFC3339)
-	bonus := gitAgeBonus(date)
+	bonus := gitAgeBonus(gitAgeBonusAnchor(-1, 0))
 	if bonus != 0 {
 		t.Errorf("expected bonus 0 for exactly 12 months, got %d", bonus)
 	}
 }
 
 func TestGitAgeBonus11Months(t *testing.T) {
-	date := time.Now().AddDate(0, -11, 0).Format(time.RFC3339)
-	bonus := gitAgeBonus(date)
+	bonus := gitAgeBonus(gitAgeBonusAnchor(0, -11))
 	if bonus != 0 {
 		t.Errorf("expected bonus 0 for 11 months, got %d", bonus)
 	}
 }
 
 func TestGitAgeBonus13Months(t *testing.T) {
-	date := time.Now().AddDate(-1, -1, 0).Format(time.RFC3339)
-	bonus := gitAgeBonus(date)
+	bonus := gitAgeBonus(gitAgeBonusAnchor(-1, -1))
 	if bonus != 5 {
 		t.Errorf("expected bonus 5 for 13 months, got %d", bonus)
 	}