feat: add bounded process metrics and private monitoring endpoint

internal/config/config.go

@@ -9,15 +9,16 @@ import (
 )
 
 type Config struct {
-	HTTPAddr string
-	MySQLDSN string
-	MaxOpen  int
-	MaxIdle  int
+	HTTPAddr    string
+	MySQLDSN    string
+	MaxOpen     int
+	MaxIdle     int
+	MetricsAddr string
 }
 
 func Load() (Config, error) { return FromEnv(os.Getenv) }
 func FromEnv(get func(string) string) (Config, error) {
-	c := Config{HTTPAddr: get("ORBIT_HTTP_ADDR"), MySQLDSN: get("ORBIT_MYSQL_DSN"), MaxOpen: 20, MaxIdle: 5}
+	c := Config{HTTPAddr: get("ORBIT_HTTP_ADDR"), MySQLDSN: get("ORBIT_MYSQL_DSN"), MaxOpen: 20, MaxIdle: 5, MetricsAddr: get("ORBIT_METRICS_ADDR")}
 	if c.HTTPAddr == "" {
 		c.HTTPAddr = "127.0.0.1:8080"
 	}
@@ -42,5 +43,12 @@ func FromEnv(get func(string) string) (Config, error) {
 	if c.MaxOpen <= 0 || c.MaxIdle > c.MaxOpen {
 		return Config{}, errors.New("database pool requires 0 <= max_idle <= max_open and max_open > 0")
 	}
+	if c.MetricsAddr != "" {
+		_, port, err := net.SplitHostPort(c.MetricsAddr)
+		n, parseErr := strconv.Atoi(port)
+		if err != nil || parseErr != nil || n < 0 || n > 65535 {
+			return Config{}, errors.New("invalid ORBIT_METRICS_ADDR")
+		}
+	}
 	return c, nil
 }

internal/config/config_test.go

@@ -0,0 +1,25 @@
+package config
+
+import "testing"
+
+func TestMetricsAddressIsExplicitAndValidated(t *testing.T) {
+	base := map[string]string{"ORBIT_MYSQL_DSN": "private-dsn"}
+	get := func(k string) string { return base[k] }
+	c, err := FromEnv(get)
+	if err != nil || c.MetricsAddr != "" {
+		t.Fatal("metrics must be disabled by default", err)
+	}
+	for _, addr := range []string{"127.0.0.1:0", "[::1]:9090", "0.0.0.0:9090"} {
+		base["ORBIT_METRICS_ADDR"] = addr
+		c, err = FromEnv(get)
+		if err != nil || c.MetricsAddr != addr {
+			t.Fatal("valid explicit address rejected", addr, err)
+		}
+	}
+	for _, addr := range []string{"bad", ":secret", "127.0.0.1:-1", ":65536", "http://127.0.0.1:9000"} {
+		base["ORBIT_METRICS_ADDR"] = addr
+		if _, err = FromEnv(get); err == nil {
+			t.Fatal("invalid address accepted", addr)
+		}
+	}
+}