diff --git a/internal/app/commands_test.go b/internal/app/commands_test.go
index 8387f5b..4d0438f 100644
--- a/internal/app/commands_test.go
+++ b/internal/app/commands_test.go
@@ -13,7 +13,8 @@ import (
 )
 
 func TestExecuteValidCommands(t *testing.T) {
-	pipelinePath, sessionPath := writeValidConfigFiles(t)
+	workspaceRoot := t.TempDir()
+	pipelinePath, sessionPath := writeValidConfigFiles(t, workspaceRoot)
 	manifestPath := writeManifestPathForExecute(t)
 
 	cases := []struct {
@@ -22,7 +23,7 @@ func TestExecuteValidCommands(t *testing.T) {
 		wantOut string
 	}{
 		{name: "run", args: []string{"run", "--config", pipelinePath, "--session", sessionPath}, wantOut: "narratio run: configuration loaded and valid"},
-		{name: "plan", args: []string{"plan", "--config", pipelinePath, "--session", sessionPath}, wantOut: "narratio plan: configuration loaded and valid"},
+		{name: "plan", args: []string{"plan", "--config", pipelinePath, "--session", sessionPath}, wantOut: "narratio plan: configuration loaded and valid; workdir prepared at"},
 		{name: "status", args: []string{"status", "--manifest", manifestPath}, wantOut: "session_id: 2026-05-03"},
 		{name: "resume", args: []string{"resume"}, wantOut: "narratio resume: not yet implemented"},
 		{name: "run-stage", args: []string{"run-stage", "polish"}, wantOut: "narratio run-stage: not yet implemented"},
@@ -113,7 +114,7 @@ func TestExecuteMissingCommand(t *testing.T) {
 	}
 }
 
-func writeValidConfigFiles(t *testing.T) (string, string) {
+func writeValidConfigFiles(t *testing.T, workspaceRoot string) (string, string) {
 	t.Helper()
 
 	dir := t.TempDir()
@@ -121,7 +122,7 @@ func writeValidConfigFiles(t *testing.T) (string, string) {
 	sessionPath := filepath.Join(dir, "session.yml")
 
 	pipelineYAML := `workspace:
-  root: /tmp/narratio
+  root: ` + workspaceRoot + `
 storage:
   backend: s3
 whisperx:
diff --git a/internal/app/plan.go b/internal/app/plan.go
index 2e21439..de2456a 100644
--- a/internal/app/plan.go
+++ b/internal/app/plan.go
@@ -6,10 +6,11 @@ import (
 	"fmt"
 	"io"
 
+	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
 	"gitea.maximumdirect.net/eric/narratio/internal/config"
 )
 
-// Plan validates configuration inputs and reports readiness for future planning.
+// Plan validates configuration inputs and prepares the local session workdir.
 func Plan(_ context.Context, args []string, out io.Writer) error {
 	fs := flag.NewFlagSet("plan", flag.ContinueOnError)
 	fs.SetOutput(io.Discard)
@@ -37,6 +38,12 @@ func Plan(_ context.Context, args []string, out io.Writer) error {
 		return fmt.Errorf("plan: %w", err)
 	}
 
-	_, err = fmt.Fprintln(out, "narratio plan: configuration loaded and valid")
+	store := artifacts.NewLocalStore(cfg.Pipeline.Workspace.Root)
+	paths, err := store.EnsureLayout(cfg.Session.SessionID)
+	if err != nil {
+		return fmt.Errorf("plan: prepare workdir: %w", err)
+	}
+
+	_, err = fmt.Fprintf(out, "narratio plan: configuration loaded and valid; workdir prepared at %s\n", paths.Root)
 	return err
 }
diff --git a/internal/app/plan_test.go b/internal/app/plan_test.go
new file mode 100644
index 0000000..34d5c39
--- /dev/null
+++ b/internal/app/plan_test.go
@@ -0,0 +1,61 @@
+package app
+
+import (
+	"bytes"
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
+)
+
+func TestPlanCreatesAndReusesWorkdir(t *testing.T) {
+	workspaceRoot := t.TempDir()
+	pipelinePath, sessionPath := writeValidConfigFiles(t, workspaceRoot)
+
+	var out bytes.Buffer
+	args := []string{"--config", pipelinePath, "--session", sessionPath}
+
+	if err := Plan(context.Background(), args, &out); err != nil {
+		t.Fatalf("first Plan() error = %v", err)
+	}
+	if !strings.Contains(out.String(), "workdir prepared") {
+		t.Fatalf("first output = %q, want workdir prepared", out.String())
+	}
+
+	sessionWorkdir := artifacts.SessionWorkDir(workspaceRoot, "2026-05-03")
+	expectedDirs := []string{
+		sessionWorkdir,
+		filepath.Join(sessionWorkdir, "inputs"),
+		filepath.Join(sessionWorkdir, "audio"),
+		filepath.Join(sessionWorkdir, "transcripts", "raw"),
+		filepath.Join(sessionWorkdir, "transcripts", "normalized"),
+		filepath.Join(sessionWorkdir, "artifacts"),
+		filepath.Join(sessionWorkdir, "config"),
+		filepath.Join(sessionWorkdir, "logs"),
+	}
+	for _, dir := range expectedDirs {
+		assertDir(t, dir)
+	}
+
+	out.Reset()
+	if err := Plan(context.Background(), args, &out); err != nil {
+		t.Fatalf("second Plan() error = %v", err)
+	}
+	if !strings.Contains(out.String(), "workdir prepared") {
+		t.Fatalf("second output = %q, want workdir prepared", out.String())
+	}
+}
+
+func assertDir(t *testing.T, path string) {
+	t.Helper()
+	info, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("Stat(%q) error = %v", path, err)
+	}
+	if !info.IsDir() {
+		t.Fatalf("%q is not a directory", path)
+	}
+}
diff --git a/internal/artifacts/local.go b/internal/artifacts/local.go
index 76dcf63..ebc0d0f 100644
--- a/internal/artifacts/local.go
+++ b/internal/artifacts/local.go
@@ -1,31 +1,291 @@
 package artifacts
 
 import (
-	"context"
+	"errors"
 	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
 )
 
-// LocalStore is a placeholder local filesystem artifact store.
+// ErrLockConflict is returned when a session lock already exists.
+var ErrLockConflict = errors.New("session workdir is already locked")
+
+// LockHandle tracks a held lock for a session work directory.
+type LockHandle struct {
+	path string
+	file *os.File
+}
+
+// LocalStore stores artifacts and session working state on the local filesystem.
 type LocalStore struct {
-	RootDir string
+	WorkspaceRoot string
 }
 
-// WriteLocal returns a not-yet-implemented error in the scaffold.
-func (s *LocalStore) WriteLocal(_ context.Context, _ Ref, _ []byte) error {
-	return fmt.Errorf("artifacts local write: not yet implemented")
+// NewLocalStore constructs a local store rooted at workspaceRoot.
+func NewLocalStore(workspaceRoot string) *LocalStore {
+	return &LocalStore{WorkspaceRoot: workspaceRoot}
 }
 
-// ReadLocal returns a not-yet-implemented error in the scaffold.
-func (s *LocalStore) ReadLocal(_ context.Context, _ Ref) ([]byte, error) {
-	return nil, fmt.Errorf("artifacts local read: not yet implemented")
+// SessionPaths resolves canonical paths for a session workdir.
+func (s *LocalStore) SessionPaths(sessionID string) SessionPaths {
+	return buildSessionPaths(s.WorkspaceRoot, sessionID)
 }
 
-// ExistsLocal returns a not-yet-implemented error in the scaffold.
-func (s *LocalStore) ExistsLocal(_ context.Context, _ Ref) (bool, error) {
-	return false, fmt.Errorf("artifacts local exists: not yet implemented")
+// EnsureLayout creates and verifies the canonical session workdir directory layout.
+func (s *LocalStore) EnsureLayout(sessionID string) (SessionPaths, error) {
+	if strings.TrimSpace(s.WorkspaceRoot) == "" {
+		return SessionPaths{}, fmt.Errorf("workspace root is required")
+	}
+	if strings.TrimSpace(sessionID) == "" {
+		return SessionPaths{}, fmt.Errorf("sessionID is required")
+	}
+
+	paths := s.SessionPaths(sessionID)
+	dirs := []string{
+		paths.Root,
+		paths.InputsDir,
+		paths.AudioDir,
+		paths.TranscriptsDir,
+		paths.TranscriptsRawDir,
+		paths.TranscriptsNormalizedDir,
+		paths.ArtifactsDir,
+		paths.ConfigDir,
+		paths.LogsDir,
+	}
+
+	for _, dir := range dirs {
+		if err := os.MkdirAll(dir, 0o755); err != nil {
+			return SessionPaths{}, fmt.Errorf("ensure layout: create %q: %w", dir, err)
+		}
+	}
+
+	return paths, nil
 }
 
-// Upload returns a not-yet-implemented error in the scaffold.
-func (s *LocalStore) Upload(_ context.Context, _ Ref) (string, error) {
-	return "", fmt.Errorf("artifacts local upload: not yet implemented")
+// CopyInput copies an input file into the session workdir under destRelativePath.
+func (s *LocalStore) CopyInput(sessionID, srcPath, destRelativePath string) (Ref, error) {
+	paths, err := s.EnsureLayout(sessionID)
+	if err != nil {
+		return Ref{}, err
+	}
+
+	destAbs, err := resolveInRoot(paths.Root, destRelativePath)
+	if err != nil {
+		return Ref{}, fmt.Errorf("copy input: %w", err)
+	}
+
+	if err := copyFileAtomic(srcPath, destAbs, 0o644); err != nil {
+		return Ref{}, fmt.Errorf("copy input %q -> %q: %w", srcPath, destAbs, err)
+	}
+
+	checksum, err := s.Checksum(destAbs)
+	if err != nil {
+		return Ref{}, fmt.Errorf("copy input checksum %q: %w", destAbs, err)
+	}
+
+	return Ref{
+		Kind:         "input",
+		Category:     "inputs",
+		SessionID:    sessionID,
+		RelativePath: filepath.Clean(destRelativePath),
+		AbsolutePath: destAbs,
+		Checksum:     checksum,
+	}, nil
+}
+
+// Exists reports whether path exists.
+func (s *LocalStore) Exists(path string) (bool, error) {
+	_, err := os.Stat(path)
+	if err == nil {
+		return true, nil
+	}
+	if errors.Is(err, os.ErrNotExist) {
+		return false, nil
+	}
+	return false, fmt.Errorf("exists %q: %w", path, err)
+}
+
+// ExistsRef reports whether ref.AbsolutePath exists.
+func (s *LocalStore) ExistsRef(ref Ref) (bool, error) {
+	if strings.TrimSpace(ref.AbsolutePath) == "" {
+		return false, fmt.Errorf("exists ref: absolute path is required")
+	}
+	return s.Exists(ref.AbsolutePath)
+}
+
+// WriteFileAtomic writes a file via temp-file + rename within the same directory.
+func (s *LocalStore) WriteFileAtomic(path string, data []byte, perm os.FileMode) error {
+	if strings.TrimSpace(path) == "" {
+		return fmt.Errorf("write file atomic: path is required")
+	}
+
+	dir := filepath.Dir(path)
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return fmt.Errorf("write file atomic: create parent dir %q: %w", dir, err)
+	}
+
+	base := filepath.Base(path)
+	tmp, err := os.CreateTemp(dir, "."+base+".tmp-*")
+	if err != nil {
+		return fmt.Errorf("write file atomic: create temp file: %w", err)
+	}
+	tmpName := tmp.Name()
+	removeTmp := true
+	defer func() {
+		if removeTmp {
+			_ = os.Remove(tmpName)
+		}
+	}()
+
+	if _, err := tmp.Write(data); err != nil {
+		_ = tmp.Close()
+		return fmt.Errorf("write file atomic: write temp file: %w", err)
+	}
+	if err := tmp.Sync(); err != nil {
+		_ = tmp.Close()
+		return fmt.Errorf("write file atomic: sync temp file: %w", err)
+	}
+	if err := tmp.Close(); err != nil {
+		return fmt.Errorf("write file atomic: close temp file: %w", err)
+	}
+
+	if err := os.Chmod(tmpName, perm); err != nil {
+		return fmt.Errorf("write file atomic: chmod temp file: %w", err)
+	}
+	if err := os.Rename(tmpName, path); err != nil {
+		return fmt.Errorf("write file atomic: rename temp file: %w", err)
+	}
+	removeTmp = false
+
+	return nil
+}
+
+// Checksum computes SHA-256 for a file path.
+func (s *LocalStore) Checksum(path string) (string, error) {
+	digest, err := SHA256File(path)
+	if err != nil {
+		return "", fmt.Errorf("checksum %q: %w", path, err)
+	}
+	return digest, nil
+}
+
+// AcquireSessionLock acquires an exclusive lock file for a session workdir.
+func (s *LocalStore) AcquireSessionLock(sessionID string) (*LockHandle, error) {
+	paths, err := s.EnsureLayout(sessionID)
+	if err != nil {
+		return nil, err
+	}
+
+	f, err := os.OpenFile(paths.LockPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o644)
+	if err != nil {
+		if errors.Is(err, os.ErrExist) {
+			return nil, fmt.Errorf("%w: %s", ErrLockConflict, paths.LockPath)
+		}
+		return nil, fmt.Errorf("acquire lock %q: %w", paths.LockPath, err)
+	}
+
+	metadata := "pid=" + strconv.Itoa(os.Getpid()) + "\nacquired_at=" + time.Now().UTC().Format(time.RFC3339Nano) + "\n"
+	if _, err := io.WriteString(f, metadata); err != nil {
+		_ = f.Close()
+		_ = os.Remove(paths.LockPath)
+		return nil, fmt.Errorf("acquire lock %q: write metadata: %w", paths.LockPath, err)
+	}
+	if err := f.Sync(); err != nil {
+		_ = f.Close()
+		_ = os.Remove(paths.LockPath)
+		return nil, fmt.Errorf("acquire lock %q: sync: %w", paths.LockPath, err)
+	}
+
+	return &LockHandle{path: paths.LockPath, file: f}, nil
+}
+
+// ReleaseSessionLock releases a previously acquired session lock.
+func (s *LocalStore) ReleaseSessionLock(lock *LockHandle) error {
+	if lock == nil {
+		return nil
+	}
+
+	var closeErr error
+	if lock.file != nil {
+		closeErr = lock.file.Close()
+		lock.file = nil
+	}
+
+	removeErr := os.Remove(lock.path)
+	if errors.Is(removeErr, os.ErrNotExist) {
+		removeErr = nil
+	}
+
+	if closeErr != nil {
+		return fmt.Errorf("release lock %q: close: %w", lock.path, closeErr)
+	}
+	if removeErr != nil {
+		return fmt.Errorf("release lock %q: remove: %w", lock.path, removeErr)
+	}
+	return nil
+}
+
+func resolveInRoot(root, relative string) (string, error) {
+	rel := filepath.Clean(relative)
+	if rel == "." || rel == "" {
+		return "", fmt.Errorf("relative destination path is required")
+	}
+	if filepath.IsAbs(rel) {
+		return "", fmt.Errorf("relative destination must not be absolute: %q", relative)
+	}
+	if rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) {
+		return "", fmt.Errorf("relative destination escapes root: %q", relative)
+	}
+	return filepath.Join(root, rel), nil
+}
+
+func copyFileAtomic(srcPath, dstPath string, perm os.FileMode) error {
+	src, err := os.Open(srcPath)
+	if err != nil {
+		return err
+	}
+	defer src.Close()
+
+	if err := os.MkdirAll(filepath.Dir(dstPath), 0o755); err != nil {
+		return err
+	}
+
+	dir := filepath.Dir(dstPath)
+	base := filepath.Base(dstPath)
+	tmp, err := os.CreateTemp(dir, "."+base+".tmp-*")
+	if err != nil {
+		return err
+	}
+	tmpName := tmp.Name()
+	removeTmp := true
+	defer func() {
+		if removeTmp {
+			_ = os.Remove(tmpName)
+		}
+	}()
+
+	if _, err := io.Copy(tmp, src); err != nil {
+		_ = tmp.Close()
+		return err
+	}
+	if err := tmp.Sync(); err != nil {
+		_ = tmp.Close()
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		return err
+	}
+	if err := os.Chmod(tmpName, perm); err != nil {
+		return err
+	}
+	if err := os.Rename(tmpName, dstPath); err != nil {
+		return err
+	}
+	removeTmp = false
+
+	return nil
 }
diff --git a/internal/artifacts/local_test.go b/internal/artifacts/local_test.go
new file mode 100644
index 0000000..30a68b4
--- /dev/null
+++ b/internal/artifacts/local_test.go
@@ -0,0 +1,174 @@
+package artifacts
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestEnsureLayoutCreatesExpectedDirectories(t *testing.T) {
+	store := NewLocalStore(t.TempDir())
+	paths, err := store.EnsureLayout("session-1")
+	if err != nil {
+		t.Fatalf("EnsureLayout() error = %v", err)
+	}
+
+	checkDirExists(t, paths.Root)
+	checkDirExists(t, paths.InputsDir)
+	checkDirExists(t, paths.AudioDir)
+	checkDirExists(t, paths.TranscriptsDir)
+	checkDirExists(t, paths.TranscriptsRawDir)
+	checkDirExists(t, paths.TranscriptsNormalizedDir)
+	checkDirExists(t, paths.ArtifactsDir)
+	checkDirExists(t, paths.ConfigDir)
+	checkDirExists(t, paths.LogsDir)
+
+	if filepath.Base(paths.ManifestPath) != "manifest.json" {
+		t.Fatalf("ManifestPath = %q, want basename manifest.json", paths.ManifestPath)
+	}
+	if filepath.Base(paths.LockPath) != ".lock" {
+		t.Fatalf("LockPath = %q, want basename .lock", paths.LockPath)
+	}
+}
+
+func TestChecksumCalculation(t *testing.T) {
+	store := NewLocalStore(t.TempDir())
+	path := filepath.Join(t.TempDir(), "sample.txt")
+	if err := os.WriteFile(path, []byte("hello"), 0o644); err != nil {
+		t.Fatalf("WriteFile() error = %v", err)
+	}
+
+	checksum, err := store.Checksum(path)
+	if err != nil {
+		t.Fatalf("Checksum() error = %v", err)
+	}
+	const want = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+	if checksum != want {
+		t.Fatalf("checksum = %q, want %q", checksum, want)
+	}
+}
+
+func TestLockAcquireRelease(t *testing.T) {
+	store := NewLocalStore(t.TempDir())
+
+	lock, err := store.AcquireSessionLock("session-1")
+	if err != nil {
+		t.Fatalf("AcquireSessionLock() error = %v", err)
+	}
+
+	exists, err := store.Exists(lock.path)
+	if err != nil {
+		t.Fatalf("Exists() error = %v", err)
+	}
+	if !exists {
+		t.Fatalf("expected lock file %q to exist", lock.path)
+	}
+
+	if err := store.ReleaseSessionLock(lock); err != nil {
+		t.Fatalf("ReleaseSessionLock() error = %v", err)
+	}
+
+	exists, err = store.Exists(lock.path)
+	if err != nil {
+		t.Fatalf("Exists() error = %v", err)
+	}
+	if exists {
+		t.Fatalf("expected lock file %q to be removed", lock.path)
+	}
+}
+
+func TestLockConflict(t *testing.T) {
+	store := NewLocalStore(t.TempDir())
+	lock1, err := store.AcquireSessionLock("session-1")
+	if err != nil {
+		t.Fatalf("first AcquireSessionLock() error = %v", err)
+	}
+	defer func() {
+		_ = store.ReleaseSessionLock(lock1)
+	}()
+
+	_, err = store.AcquireSessionLock("session-1")
+	if err == nil {
+		t.Fatal("expected lock conflict error, got nil")
+	}
+	if !errors.Is(err, ErrLockConflict) {
+		t.Fatalf("error = %v, want ErrLockConflict", err)
+	}
+}
+
+func TestWriteFileAtomicAndOverwrite(t *testing.T) {
+	store := NewLocalStore(t.TempDir())
+	path := filepath.Join(t.TempDir(), "out", "value.txt")
+
+	if err := store.WriteFileAtomic(path, []byte("one"), 0o644); err != nil {
+		t.Fatalf("first WriteFileAtomic() error = %v", err)
+	}
+	if err := store.WriteFileAtomic(path, []byte("two"), 0o644); err != nil {
+		t.Fatalf("second WriteFileAtomic() error = %v", err)
+	}
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("ReadFile() error = %v", err)
+	}
+	if string(data) != "two" {
+		t.Fatalf("file content = %q, want %q", string(data), "two")
+	}
+
+	entries, err := os.ReadDir(filepath.Dir(path))
+	if err != nil {
+		t.Fatalf("ReadDir() error = %v", err)
+	}
+	for _, e := range entries {
+		if strings.Contains(e.Name(), ".tmp-") {
+			t.Fatalf("unexpected temp file residue: %s", e.Name())
+		}
+	}
+}
+
+func TestCopyInput(t *testing.T) {
+	root := t.TempDir()
+	store := NewLocalStore(root)
+
+	srcPath := filepath.Join(t.TempDir(), "speakers.yml")
+	content := "alice: alice.flac\n"
+	if err := os.WriteFile(srcPath, []byte(content), 0o644); err != nil {
+		t.Fatalf("WriteFile() error = %v", err)
+	}
+
+	ref, err := store.CopyInput("session-1", srcPath, "inputs/speakers.yml")
+	if err != nil {
+		t.Fatalf("CopyInput() error = %v", err)
+	}
+
+	if ref.Kind != "input" {
+		t.Fatalf("ref.Kind = %q, want %q", ref.Kind, "input")
+	}
+	if ref.RelativePath != filepath.Clean("inputs/speakers.yml") {
+		t.Fatalf("ref.RelativePath = %q, want %q", ref.RelativePath, filepath.Clean("inputs/speakers.yml"))
+	}
+	if !strings.HasPrefix(ref.AbsolutePath, root) {
+		t.Fatalf("ref.AbsolutePath = %q, want under workspace root %q", ref.AbsolutePath, root)
+	}
+
+	data, err := os.ReadFile(ref.AbsolutePath)
+	if err != nil {
+		t.Fatalf("ReadFile() error = %v", err)
+	}
+	if string(data) != content {
+		t.Fatalf("copied content = %q, want %q", string(data), content)
+	}
+}
+
+func checkDirExists(t *testing.T, path string) {
+	t.Helper()
+	info, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("Stat(%q) error = %v", path, err)
+	}
+	if !info.IsDir() {
+		t.Fatalf("%q is not a directory", path)
+	}
+}
diff --git a/internal/artifacts/paths.go b/internal/artifacts/paths.go
index e575440..0dea0f5 100644
--- a/internal/artifacts/paths.go
+++ b/internal/artifacts/paths.go
@@ -2,7 +2,40 @@ package artifacts
 
 import "path/filepath"
 
+// SessionPaths contains canonical local paths for one session work directory.
+type SessionPaths struct {
+	Root                     string
+	InputsDir                string
+	AudioDir                 string
+	TranscriptsDir           string
+	TranscriptsRawDir        string
+	TranscriptsNormalizedDir string
+	ArtifactsDir             string
+	ConfigDir                string
+	LogsDir                  string
+	ManifestPath             string
+	LockPath                 string
+}
+
 // SessionWorkDir returns the work directory for one session.
 func SessionWorkDir(rootDir, sessionID string) string {
 	return filepath.Join(rootDir, "work", sessionID)
 }
+
+func buildSessionPaths(workspaceRoot, sessionID string) SessionPaths {
+	root := SessionWorkDir(workspaceRoot, sessionID)
+	transcripts := filepath.Join(root, "transcripts")
+	return SessionPaths{
+		Root:                     root,
+		InputsDir:                filepath.Join(root, "inputs"),
+		AudioDir:                 filepath.Join(root, "audio"),
+		TranscriptsDir:           transcripts,
+		TranscriptsRawDir:        filepath.Join(transcripts, "raw"),
+		TranscriptsNormalizedDir: filepath.Join(transcripts, "normalized"),
+		ArtifactsDir:             filepath.Join(root, "artifacts"),
+		ConfigDir:                filepath.Join(root, "config"),
+		LogsDir:                  filepath.Join(root, "logs"),
+		ManifestPath:             filepath.Join(root, "manifest.json"),
+		LockPath:                 filepath.Join(root, ".lock"),
+	}
+}
diff --git a/internal/artifacts/s3.go b/internal/artifacts/s3.go
index 8353596..56331a9 100644
--- a/internal/artifacts/s3.go
+++ b/internal/artifacts/s3.go
@@ -1,32 +1,57 @@
 package artifacts
 
 import (
-	"context"
 	"fmt"
+	"os"
 )
 
-// S3Store is a placeholder S3-compatible artifact store.
+// S3Store is a placeholder for future remote artifact persistence support.
 type S3Store struct {
 	Bucket string
 	Prefix string
 }
 
-// WriteLocal returns a not-yet-implemented error in the scaffold.
-func (s *S3Store) WriteLocal(_ context.Context, _ Ref, _ []byte) error {
-	return fmt.Errorf("artifacts s3 write local: not yet implemented")
+// SessionPaths is not implemented for S3-backed storage.
+func (s *S3Store) SessionPaths(_ string) SessionPaths {
+	return SessionPaths{}
 }
 
-// ReadLocal returns a not-yet-implemented error in the scaffold.
-func (s *S3Store) ReadLocal(_ context.Context, _ Ref) ([]byte, error) {
-	return nil, fmt.Errorf("artifacts s3 read local: not yet implemented")
+// EnsureLayout returns a not-yet-implemented error in the scaffold.
+func (s *S3Store) EnsureLayout(_ string) (SessionPaths, error) {
+	return SessionPaths{}, fmt.Errorf("artifacts s3 ensure layout: not yet implemented")
 }
 
-// ExistsLocal returns a not-yet-implemented error in the scaffold.
-func (s *S3Store) ExistsLocal(_ context.Context, _ Ref) (bool, error) {
-	return false, fmt.Errorf("artifacts s3 exists local: not yet implemented")
+// CopyInput returns a not-yet-implemented error in the scaffold.
+func (s *S3Store) CopyInput(_, _, _ string) (Ref, error) {
+	return Ref{}, fmt.Errorf("artifacts s3 copy input: not yet implemented")
 }
 
-// Upload returns a not-yet-implemented error in the scaffold.
-func (s *S3Store) Upload(_ context.Context, _ Ref) (string, error) {
-	return "", fmt.Errorf("artifacts s3 upload: not yet implemented")
+// Exists returns a not-yet-implemented error in the scaffold.
+func (s *S3Store) Exists(_ string) (bool, error) {
+	return false, fmt.Errorf("artifacts s3 exists: not yet implemented")
+}
+
+// ExistsRef returns a not-yet-implemented error in the scaffold.
+func (s *S3Store) ExistsRef(_ Ref) (bool, error) {
+	return false, fmt.Errorf("artifacts s3 exists ref: not yet implemented")
+}
+
+// WriteFileAtomic returns a not-yet-implemented error in the scaffold.
+func (s *S3Store) WriteFileAtomic(_ string, _ []byte, _ os.FileMode) error {
+	return fmt.Errorf("artifacts s3 write file atomic: not yet implemented")
+}
+
+// Checksum returns a not-yet-implemented error in the scaffold.
+func (s *S3Store) Checksum(_ string) (string, error) {
+	return "", fmt.Errorf("artifacts s3 checksum: not yet implemented")
+}
+
+// AcquireSessionLock returns a not-yet-implemented error in the scaffold.
+func (s *S3Store) AcquireSessionLock(_ string) (*LockHandle, error) {
+	return nil, fmt.Errorf("artifacts s3 acquire lock: not yet implemented")
+}
+
+// ReleaseSessionLock returns a not-yet-implemented error in the scaffold.
+func (s *S3Store) ReleaseSessionLock(_ *LockHandle) error {
+	return fmt.Errorf("artifacts s3 release lock: not yet implemented")
 }
diff --git a/internal/artifacts/store.go b/internal/artifacts/store.go
index c5396d3..7a8445d 100644
--- a/internal/artifacts/store.go
+++ b/internal/artifacts/store.go
@@ -1,19 +1,27 @@
 package artifacts
 
-import "context"
+import "os"
 
-// Ref identifies a pipeline artifact and optional remote location.
+// Ref identifies a pipeline artifact and its local/remote coordinates.
 type Ref struct {
-	Kind      string
-	LocalPath string
-	RemoteKey string
-	Checksum  string
+	Kind         string
+	Category     string
+	SessionID    string
+	RelativePath string
+	AbsolutePath string
+	RemoteKey    string
+	Checksum     string
 }
 
-// Store is a placeholder artifact storage abstraction.
+// Store is the local artifact/workdir abstraction used by orchestration code.
 type Store interface {
-	WriteLocal(ctx context.Context, ref Ref, data []byte) error
-	ReadLocal(ctx context.Context, ref Ref) ([]byte, error)
-	ExistsLocal(ctx context.Context, ref Ref) (bool, error)
-	Upload(ctx context.Context, ref Ref) (string, error)
+	SessionPaths(sessionID string) SessionPaths
+	EnsureLayout(sessionID string) (SessionPaths, error)
+	CopyInput(sessionID, srcPath, destRelativePath string) (Ref, error)
+	Exists(path string) (bool, error)
+	ExistsRef(ref Ref) (bool, error)
+	WriteFileAtomic(path string, data []byte, perm os.FileMode) error
+	Checksum(path string) (string, error)
+	AcquireSessionLock(sessionID string) (*LockHandle, error)
+	ReleaseSessionLock(lock *LockHandle) error
 }