feat(codeagent-wrapper): add --output structured JSON file (#151)

* feat(codeagent-wrapper): add --output structured JSON file

* fix(codeagent-wrapper): write --output on failure

---------

Co-authored-by: danielee.eth <danielee.eth@gmail.com>
Co-authored-by: cexll <evanxian9@gmail.com>

codeagent-wrapper/internal/app/output_file.go

@@ -0,0 +1,65 @@
+package wrapper
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/goccy/go-json"
+)
+
+type outputSummary struct {
+	Total   int `json:"total"`
+	Success int `json:"success"`
+	Failed  int `json:"failed"`
+}
+
+type outputPayload struct {
+	Results []TaskResult  `json:"results"`
+	Summary outputSummary `json:"summary"`
+}
+
+func writeStructuredOutput(path string, results []TaskResult) error {
+	path = strings.TrimSpace(path)
+	if path == "" {
+		return nil
+	}
+
+	cleanPath := filepath.Clean(path)
+	dir := filepath.Dir(cleanPath)
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return fmt.Errorf("failed to create output directory for %q: %w", cleanPath, err)
+	}
+
+	f, err := os.Create(cleanPath)
+	if err != nil {
+		return fmt.Errorf("failed to create output file %q: %w", cleanPath, err)
+	}
+
+	encodeErr := json.NewEncoder(f).Encode(outputPayload{
+		Results: results,
+		Summary: summarizeResults(results),
+	})
+	closeErr := f.Close()
+
+	if encodeErr != nil {
+		return fmt.Errorf("failed to write structured output to %q: %w", cleanPath, encodeErr)
+	}
+	if closeErr != nil {
+		return fmt.Errorf("failed to close output file %q: %w", cleanPath, closeErr)
+	}
+	return nil
+}
+
+func summarizeResults(results []TaskResult) outputSummary {
+	summary := outputSummary{Total: len(results)}
+	for _, res := range results {
+		if res.ExitCode == 0 && res.Error == "" {
+			summary.Success++
+		} else {
+			summary.Failed++
+		}
+	}
+	return summary
+}