fix(config): reject non-positive integer settings

cmd/agentbbs/main.go

@@ -99,10 +99,10 @@ func env(k, def string) string {
 	return def
 }
 
-// envInt reads an integer environment variable, falling back to def.
+// envInt reads a positive integer environment variable, falling back to def.
 func envInt(k string, def int) int {
 	if v := os.Getenv(k); v != "" {
-		if n, err := strconv.Atoi(v); err == nil {
+		if n, err := strconv.Atoi(v); err == nil && n > 0 {
 			return n
 		}
 	}

cmd/agentbbs/main_test.go

@@ -2,6 +2,22 @@ package main
 
 import "testing"
 
+func TestEnvIntRequiresPositiveValue(t *testing.T) {
+	const key = "AGENTBBS_TEST_POSITIVE_INT"
+
+	for _, value := range []string{"", "invalid", "0", "-1"} {
+		t.Setenv(key, value)
+		if got := envInt(key, 15); got != 15 {
+			t.Errorf("envInt(%q, 15) with %q = %d, want 15", key, value, got)
+		}
+	}
+
+	t.Setenv(key, "30")
+	if got := envInt(key, 15); got != 30 {
+		t.Errorf("envInt(%q, 15) = %d, want 30", key, got)
+	}
+}
+
 func TestValidIRCServerPortRange(t *testing.T) {
 	for _, server := range []string{
 		"irc.example.com",