Always rebuild the gateway in make build; migrate legacy providers by activation

internal/config/config.go

@@ -174,8 +174,13 @@ func (c *Config) normalize() {
 		case TargetClaude, TargetCodex:
 		default:
 			// Providers created before targets existed belong to the
-			// Claude page.
-			c.Providers[i].Target = TargetClaude
+			// Claude page, unless they were only ever activated for
+			// Codex.
+			if c.Providers[i].EnabledForCodex && !c.Providers[i].EnabledForClaude {
+				c.Providers[i].Target = TargetCodex
+			} else {
+				c.Providers[i].Target = TargetClaude
+			}
 		}
 	}
 	switch c.Gateway.PortMode {

internal/config/config_test.go

@@ -1,6 +1,8 @@
 package config
 
 import (
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 )
@@ -221,6 +223,42 @@ func TestUpdateProviderKeepsEnabledFlags(t *testing.T) {
 	}
 }
 
+func TestProviderTargetMigration(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("CROSSRELAY_HOME", home)
+	legacy := `{
+  "version": 1,
+  "relay_token": "crl_legacy",
+  "providers": [
+    {"id":"p_1","name":"claude-side","base_url":"https://a.example.com/v1","api_key":"sk","models":{"default":"m"},"enabled_for_claude":true,"created_at":"2026-10-01T00:00:00Z"},
+    {"id":"p_2","name":"codex-side","base_url":"https://b.example.com/v1","api_key":"sk","models":{"default":"m"},"enabled_for_codex":true,"created_at":"2026-10-01T00:00:00Z"},
+    {"id":"p_3","name":"never-active","base_url":"https://c.example.com/v1","api_key":"sk","models":{"default":"m"},"created_at":"2026-10-01T00:00:00Z"}
+  ],
+  "gateway": {"port_mode": "auto"},
+  "language": "zh-CN"
+}`
+	if err := os.WriteFile(filepath.Join(home, "config.json"), []byte(legacy), 0o600); err != nil {
+		t.Fatalf("write legacy config: %v", err)
+	}
+	store, err := Load()
+	if err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+	targets := map[string]string{}
+	for _, p := range store.Config().Providers {
+		targets[p.Name] = p.Target
+	}
+	if targets["claude-side"] != TargetClaude {
+		t.Errorf("claude-side target = %q, want claude", targets["claude-side"])
+	}
+	if targets["codex-side"] != TargetCodex {
+		t.Errorf("codex-side target = %q, want codex", targets["codex-side"])
+	}
+	if targets["never-active"] != TargetClaude {
+		t.Errorf("never-active target = %q, want claude", targets["never-active"])
+	}
+}
+
 func TestProviderTargetDefaultsAndValidation(t *testing.T) {
 	t.Setenv("CROSSRELAY_HOME", t.TempDir())
 	store, err := Load()