Add runtime abstraction and agent loop

Co-authored-by: codegirl007 <codegirl-007@users.noreply.github.com>

agentbox/internal/appspec/appspec.go

@@ -0,0 +1,64 @@
+package appspec
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"agentbox/internal/environment"
+)
+
+type manifest struct {
+	Command     string            `json:"command"`
+	Args        []string          `json:"args"`
+	Env         map[string]string `json:"env"`
+	WindowTitle string            `json:"window_title"`
+}
+
+func Resolve(path string) (environment.Command, error) {
+	absolute, err := filepath.Abs(path)
+	if err != nil {
+		return environment.Command{}, fmt.Errorf("resolve application path: %w", err)
+	}
+	info, err := os.Stat(absolute)
+	if err != nil {
+		return environment.Command{}, fmt.Errorf("inspect application path: %w", err)
+	}
+	if !info.IsDir() {
+		if !info.Mode().IsRegular() {
+			return environment.Command{}, errors.New("application must be a regular executable file")
+		}
+		return environment.Command{Path: absolute}, nil
+	}
+
+	data, err := os.ReadFile(filepath.Join(absolute, "agentbox.json"))
+	if err != nil {
+		return environment.Command{}, fmt.Errorf("read directory manifest agentbox.json: %w", err)
+	}
+	var config manifest
+	if err := json.Unmarshal(data, &config); err != nil {
+		return environment.Command{}, fmt.Errorf("parse agentbox.json: %w", err)
+	}
+	if config.Command == "" {
+		return environment.Command{}, errors.New("agentbox.json requires command")
+	}
+	commandPath := config.Command
+	if !filepath.IsAbs(commandPath) {
+		commandPath = filepath.Join(absolute, commandPath)
+	}
+	commandInfo, err := os.Stat(commandPath)
+	if err != nil {
+		return environment.Command{}, fmt.Errorf("inspect manifest command: %w", err)
+	}
+	if !commandInfo.Mode().IsRegular() {
+		return environment.Command{}, errors.New("manifest command must be a regular executable file")
+	}
+	return environment.Command{
+		Path:        commandPath,
+		Args:        config.Args,
+		Env:         config.Env,
+		WindowTitle: config.WindowTitle,
+	}, nil
+}