feat: run --summary via agent CLI (claude -p by default)

internal/engine/engine.go

@@ -253,7 +253,7 @@ func Run(opts Options) (*Result, error) {
 		if !opts.Quiet {
 			fmt.Println("[stacklit] generating AI summary...")
 		}
-		text, summaryErr := summary.Generate(idx)
+		text, summaryErr := summary.Run(idx)
 		if summaryErr != nil {
 			fmt.Printf("[stacklit] warning: summary failed: %v\n", summaryErr)
 		} else {

internal/summary/cli.go

@@ -0,0 +1,79 @@
+package summary
+
+import (
+	"bytes"
+	"cmp"
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/glincker/stacklit/internal/schema"
+)
+
+const (
+	envCmd     = "STACKLIT_SUMMARY_CMD"
+	envTimeout = "STACKLIT_SUMMARY_TIMEOUT"
+
+	defaultTimeoutSec = 120
+	stderrTail        = 500
+)
+
+// Run invokes the configured agent CLI
+func Run(idx *schema.Index) (string, error) {
+	command := []string{"claude", "-p"}
+	if parts := strings.Fields(os.Getenv(envCmd)); len(parts) > 0 {
+		command = parts
+	}
+
+	n, _ := strconv.Atoi(strings.TrimSpace(os.Getenv(envTimeout)))
+	timeout := time.Duration(cmp.Or(max(n, 0), defaultTimeoutSec)) * time.Second
+
+	snapshot := indexSnapshot{
+		Project:      idx.Project,
+		Tech:         idx.Tech,
+		Modules:      idx.Modules,
+		Dependencies: idx.Dependencies,
+		Entrypoints:  idx.Structure.Entrypoints,
+	}
+
+	userJSON, err := json.Marshal(snapshot)
+	if err != nil {
+		return "", fmt.Errorf("marshalling index snapshot: %w", err)
+	}
+
+	// Most agent CLIs lack a stdin system-prompt channel, so prepend inline.
+	prompt := systemPrompt + "\n\n" + string(userJSON)
+
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	cmd := exec.CommandContext(ctx, command[0], command[1:]...)
+	cmd.Stdin = strings.NewReader(prompt)
+
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+
+	err = cmd.Run()
+	if ctx.Err() == context.DeadlineExceeded {
+		return "", fmt.Errorf("summary CLI %q timed out after %s", command[0], timeout)
+	}
+
+	if err != nil {
+		return "", fmt.Errorf("summary CLI %q failed: %w: %.*s",
+			command[0], err, stderrTail, strings.TrimSpace(stderr.String()))
+	}
+
+	text := strings.TrimSpace(stdout.String())
+	if text == "" {
+		return "", fmt.Errorf("summary CLI %q produced empty output (stderr: %.*s)",
+			command[0], stderrTail, strings.TrimSpace(stderr.String()))
+	}
+
+	return text, nil
+}