fix(agent): recover OpenResty runtime after invalid PID (#45)

* fix(agent): recover OpenResty runtime after invalid PID

* fix(agent): scope OpenResty shutdown to instance processes

---------

Co-authored-by: Noru Wyrms <wyrmsnoru@gmail.com>

internal/apps/agent/nginx/runtime_process_linux.go

@@ -0,0 +1,44 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package nginx
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"syscall"
+)
+
+func inspectOpenrestyProcesses(ctx context.Context, binary, configPath string) ([]runtimeProcess, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	path, err := exec.LookPath(binary)
+	if err != nil {
+		return nil, err
+	}
+	executable, err := os.Stat(path)
+	if err != nil {
+		return nil, err
+	}
+	return inspectProcRuntime("/proc", executable, binary, configPath, os.Geteuid())
+}
+
+func signalOpenrestyProcess(ctx context.Context, binary, config string, process runtimeProcess, quit bool) error {
+	processes, err := inspectOpenrestyProcesses(ctx, binary, config)
+	if err != nil {
+		return err
+	}
+	for _, current := range processes {
+		if current.PID == process.PID && current.Master && current.StartTime == process.StartTime {
+			signal := syscall.SIGHUP
+			if quit {
+				signal = syscall.SIGQUIT
+			}
+			return syscall.Kill(current.PID, signal)
+		}
+	}
+	return fmt.Errorf("openresty master identity changed before signalling pid %d", process.PID)
+}