Add subprocess runner and generated config helpers

internal/adapters/seriatim/fake.go

@@ -1,6 +1,11 @@
 package seriatim
 
-import "context"
+import (
+	"context"
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/adapters/subprocess"
+)
 
 // NoopRunner is a deterministic no-op seriatim adapter.
 type NoopRunner struct{}
@@ -10,6 +15,9 @@ func (n *NoopRunner) Run(ctx context.Context, req MergeRequest) (MergeResult, er
 	if err := ctx.Err(); err != nil {
 		return MergeResult{}, err
 	}
+	if err := materializePlaceholders(req); err != nil {
+		return MergeResult{}, err
+	}
 	return MergeResult{MergedTranscriptPath: req.OutputMergedTranscriptPath, Metadata: map[string]any{"placeholder": true}}, nil
 }
 
@@ -29,6 +37,9 @@ func (f *FakeRunner) Run(ctx context.Context, req MergeRequest) (MergeResult, er
 	if f.Err != nil {
 		return MergeResult{}, f.Err
 	}
+	if err := materializePlaceholders(req); err != nil {
+		return MergeResult{}, err
+	}
 	res := f.Result
 	if res.MergedTranscriptPath == "" {
 		res.MergedTranscriptPath = req.OutputMergedTranscriptPath
@@ -38,3 +49,28 @@ func (f *FakeRunner) Run(ctx context.Context, req MergeRequest) (MergeResult, er
 	}
 	return res, nil
 }
+
+func materializePlaceholders(req MergeRequest) error {
+	if req.GeneratedConfigPath != "" {
+		payload := map[string]any{
+			"schema":                 "seriatim.generated.v1",
+			"placeholder":            true,
+			"input_transcript_paths": req.InputTranscriptPaths,
+			"output_path":            req.OutputMergedTranscriptPath,
+		}
+		if err := subprocess.WriteYAMLAtomic(req.GeneratedConfigPath, payload, 0o644); err != nil {
+			return fmt.Errorf("write generated config %q: %w", req.GeneratedConfigPath, err)
+		}
+	}
+	if req.StdoutLogPath != "" {
+		if err := subprocess.WriteFileAtomic(req.StdoutLogPath, []byte("seriatim noop/fake stdout placeholder\n"), 0o644); err != nil {
+			return fmt.Errorf("write stdout log %q: %w", req.StdoutLogPath, err)
+		}
+	}
+	if req.StderrLogPath != "" {
+		if err := subprocess.WriteFileAtomic(req.StderrLogPath, []byte("seriatim noop/fake stderr placeholder\n"), 0o644); err != nil {
+			return fmt.Errorf("write stderr log %q: %w", req.StderrLogPath, err)
+		}
+	}
+	return nil
+}

internal/adapters/seriatim/fake_test.go

@@ -3,12 +3,21 @@ package seriatim
 import (
 	"context"
 	"errors"
+	"os"
+	"path/filepath"
+	"strings"
 	"testing"
 )
 
 func TestFakeRunnerCapturesRequestAndReturnsPath(t *testing.T) {
 	fake := &FakeRunner{}
-	req := MergeRequest{GeneratedConfigPath: "config/seriatim.yml", OutputMergedTranscriptPath: "transcripts/merged.json"}
+	dir := t.TempDir()
+	req := MergeRequest{
+		GeneratedConfigPath:        filepath.Join(dir, "config", "seriatim.yml"),
+		OutputMergedTranscriptPath: filepath.Join(dir, "transcripts", "merged.json"),
+		StdoutLogPath:              filepath.Join(dir, "logs", "seriatim.stdout.log"),
+		StderrLogPath:              filepath.Join(dir, "logs", "seriatim.stderr.log"),
+	}
 
 	res, err := fake.Run(context.Background(), req)
 	if err != nil {
@@ -20,6 +29,19 @@ func TestFakeRunnerCapturesRequestAndReturnsPath(t *testing.T) {
 	if res.MergedTranscriptPath != req.OutputMergedTranscriptPath {
 		t.Fatalf("merged path = %q, want %q", res.MergedTranscriptPath, req.OutputMergedTranscriptPath)
 	}
+
+	cfgData, err := os.ReadFile(req.GeneratedConfigPath)
+	if err != nil {
+		t.Fatalf("read generated config: %v", err)
+	}
+	if !strings.Contains(string(cfgData), "placeholder: true") {
+		t.Fatalf("generated config = %q, want placeholder marker", string(cfgData))
+	}
+	for _, logPath := range []string{req.StdoutLogPath, req.StderrLogPath} {
+		if _, err := os.Stat(logPath); err != nil {
+			t.Fatalf("expected log file %q to exist: %v", logPath, err)
+		}
+	}
 }
 
 func TestFakeRunnerError(t *testing.T) {