Add strict pipeline and session config loading

internal/app/plan.go

@@ -2,10 +2,41 @@ package app
 
 import (
 	"context"
+	"flag"
+	"fmt"
 	"io"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
 )
 
-// Plan is a placeholder for future stage planning behavior.
-func Plan(_ context.Context, _ []string, out io.Writer) error {
-	return placeholder(out, "plan")
+// Plan validates configuration inputs and reports readiness for future planning.
+func Plan(_ context.Context, args []string, out io.Writer) error {
+	fs := flag.NewFlagSet("plan", flag.ContinueOnError)
+	fs.SetOutput(io.Discard)
+
+	var pipelinePath string
+	var sessionPath string
+	fs.StringVar(&pipelinePath, "config", "", "path to pipeline.yml")
+	fs.StringVar(&sessionPath, "session", "", "path to session.yml")
+
+	if err := fs.Parse(args); err != nil {
+		return fmt.Errorf("plan: invalid flags: %w", err)
+	}
+	if fs.NArg() != 0 {
+		return fmt.Errorf("plan: unexpected positional arguments")
+	}
+	if pipelinePath == "" || sessionPath == "" {
+		return fmt.Errorf("plan: --config and --session are required")
+	}
+
+	cfg, err := config.Load(pipelinePath, sessionPath)
+	if err != nil {
+		return fmt.Errorf("plan: %w", err)
+	}
+	if err := config.Validate(cfg); err != nil {
+		return fmt.Errorf("plan: %w", err)
+	}
+
+	_, err = fmt.Fprintln(out, "narratio plan: configuration loaded and valid")
+	return err
 }