Add Go worker agent prototype

coordinator/internal/agent/taskrunner.go

@@ -0,0 +1,81 @@
+package agent
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+)
+
+// TaskRunner spawns the Python task entry and returns the sealed partial
+// artifact manifest it produced.
+type TaskRunner struct {
+	command []string
+}
+
+func NewTaskRunner(command []string) *TaskRunner {
+	return &TaskRunner{command: command}
+}
+
+// Run executes one task: the task payload is written as JSON into the attempt
+// directory, the Python entry computes and seals the partial, and the written
+// manifest is parsed back. stderr is captured for failure reporting.
+func (r *TaskRunner) Run(task *Task, taskDir string, manifestPath string, extraEnv []string) (*TaskRunnerManifest, error) {
+	if err := os.MkdirAll(taskDir, 0o755); err != nil {
+		return nil, err
+	}
+	payload := map[string]any{
+		"task_id":          task.TaskID,
+		"attempt":          task.Attempt,
+		"lease_expires_at": task.leaseExpiresRaw,
+		"workload":         task.Workload,
+		"input": map[string]any{
+			"uri":    task.Input.URI,
+			"sha256": task.Input.SHA256,
+		},
+		"parameters": task.Parameters,
+	}
+	payloadBytes, err := json.Marshal(payload)
+	if err != nil {
+		return nil, err
+	}
+	taskJSONPath := filepath.Join(taskDir, "task.json")
+	if err := os.WriteFile(taskJSONPath, payloadBytes, 0o600); err != nil {
+		return nil, err
+	}
+	args := append([]string{}, r.command[1:]...)
+	args = append(args,
+		"--task-json", taskJSONPath,
+		"--task-dir", taskDir,
+		"--output", manifestPath,
+	)
+	command := exec.Command(r.command[0], args...)
+	command.Dir = taskDir
+	command.Env = append(os.Environ(), extraEnv...)
+	var stderr bytes.Buffer
+	command.Stderr = &stderr
+	if err := command.Run(); err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			return nil, runnerExitError(exitErr.ExitCode(), stderr.String())
+		}
+		return nil, fmt.Errorf("task runner could not be started: %w", err)
+	}
+	raw, err := os.ReadFile(manifestPath)
+	if err != nil {
+		return nil, fmt.Errorf("task runner produced no result manifest")
+	}
+	var manifest TaskRunnerManifest
+	if err := json.Unmarshal(raw, &manifest); err != nil {
+		return nil, fmt.Errorf("task runner produced an invalid result manifest")
+	}
+	if manifest.ArtifactPath == "" || manifest.ContentType == "" {
+		return nil, fmt.Errorf("task runner produced an incomplete result manifest")
+	}
+	info, err := os.Stat(manifest.ArtifactPath)
+	if err != nil || !info.Mode().IsRegular() {
+		return nil, fmt.Errorf("task runner produced no artifact file")
+	}
+	return &manifest, nil
+}