COPY multi-source support, configurable rootfs size, build fixes

- COPY now supports multiple sources: COPY a.txt b.txt /dest/
  Last argument is always destination (matches Dockerfile semantics).
- COPY resolves relative destinations against current WORKDIR.
- WRENN_DEFAULT_ROOTFS_SIZE env var (e.g. 5G, 2Gi, 1000M, 512Mi)
  controls template rootfs expansion. Used both at agent startup
  (EnsureImageSizes) and after FlattenRootfs (shrink then re-expand).
- Pre-build now sets WORKDIR /home/wrenn-user after USER switch.
- Extracted archive files get chmod a+rX for readability.
- Path traversal validation on COPY sources.

internal/recipe/executor.go

@@ -208,25 +208,33 @@ func execCopy(
 	bctx *ExecContext,
 	execFn ExecFunc,
 ) (BuildLogEntry, bool) {
-	// Validate source path: must be relative and not escape the archive directory.
-	cleaned := path.Clean(st.Src)
-	if strings.HasPrefix(cleaned, "..") || strings.HasPrefix(cleaned, "/") {
-		return BuildLogEntry{
-			Step:   step,
-			Phase:  phase,
-			Cmd:    st.Raw,
-			Stderr: "COPY source must be a relative path within the archive",
-		}, false
+	// Validate all source paths: must be relative and not escape the archive directory.
+	var srcPaths []string
+	for _, s := range st.Srcs {
+		cleaned := path.Clean(s)
+		if strings.HasPrefix(cleaned, "..") || strings.HasPrefix(cleaned, "/") {
+			return BuildLogEntry{
+				Step:   step,
+				Phase:  phase,
+				Cmd:    st.Raw,
+				Stderr: fmt.Sprintf("COPY source must be a relative path within the archive: %q", s),
+			}, false
+		}
+		srcPaths = append(srcPaths, shellescape(BuildFilesDir+"/"+cleaned))
 	}
-	src := BuildFilesDir + "/" + cleaned
+
 	dst := st.Dst
+	// Resolve relative destination against the current WORKDIR.
+	if dst != "" && dst[0] != '/' && bctx.WorkDir != "" {
+		dst = bctx.WorkDir + "/" + dst
+	}
 	owner := "root"
 	if bctx.User != "" {
 		owner = bctx.User
 	}
 	script := fmt.Sprintf(
 		"cp -r %s %s && chown -R %s:%s %s",
-		shellescape(src), shellescape(dst), shellescape(owner), shellescape(owner), shellescape(dst),
+		strings.Join(srcPaths, " "), shellescape(dst), shellescape(owner), shellescape(owner), shellescape(dst),
 	)
 
 	entry := execRawShell(ctx, st.Raw, sandboxID, phase, step, 60*time.Second, execFn, script)

internal/recipe/step.go

@@ -27,7 +27,7 @@ type Step struct {
 	Key     string        // KindENV: variable name; KindUSER: username
 	Value   string        // KindENV: variable value
 	Path    string        // KindWORKDIR: directory path
-	Src     string        // KindCOPY: source path (relative to build archive)
+	Srcs    []string      // KindCOPY: source paths (relative to build archive)
 	Dst     string        // KindCOPY: destination path inside sandbox
 }
 
@@ -148,12 +148,14 @@ func parseUSER(raw, username string) (Step, error) {
 
 func parseCOPY(raw, rest string) (Step, error) {
 	if rest == "" {
-		return Step{}, fmt.Errorf("COPY requires <src> <dst>: %q", raw)
+		return Step{}, fmt.Errorf("COPY requires <src>... <dst>: %q", raw)
 	}
-	src, dst, found := strings.Cut(rest, " ")
-	dst = strings.TrimSpace(dst)
-	if !found || dst == "" {
-		return Step{}, fmt.Errorf("COPY requires <src> <dst>: %q", raw)
+	parts := strings.Fields(rest)
+	if len(parts) < 2 {
+		return Step{}, fmt.Errorf("COPY requires <src>... <dst>: %q", raw)
 	}
-	return Step{Kind: KindCOPY, Raw: raw, Src: src, Dst: dst}, nil
+	// Last argument is the destination, everything before is sources.
+	dst := parts[len(parts)-1]
+	srcs := parts[:len(parts)-1]
+	return Step{Kind: KindCOPY, Raw: raw, Srcs: srcs, Dst: dst}, nil
 }

internal/recipe/step_test.go

@@ -1,6 +1,7 @@
 package recipe
 
 import (
+	"reflect"
 	"testing"
 	"time"
 )
@@ -131,7 +132,12 @@ func TestParseStep(t *testing.T) {
 		{
 			name:  "COPY basic",
 			input: "COPY config.yaml /etc/app/config.yaml",
-			want:  Step{Kind: KindCOPY, Raw: "COPY config.yaml /etc/app/config.yaml", Src: "config.yaml", Dst: "/etc/app/config.yaml"},
+			want:  Step{Kind: KindCOPY, Raw: "COPY config.yaml /etc/app/config.yaml", Srcs: []string{"config.yaml"}, Dst: "/etc/app/config.yaml"},
+		},
+		{
+			name:  "COPY multiple sources",
+			input: "COPY a.txt b.txt /dest/",
+			want:  Step{Kind: KindCOPY, Raw: "COPY a.txt b.txt /dest/", Srcs: []string{"a.txt", "b.txt"}, Dst: "/dest/"},
 		},
 		{
 			name:    "COPY missing dst",
@@ -169,7 +175,7 @@ func TestParseStep(t *testing.T) {
 			if err != nil {
 				t.Fatalf("ParseStep(%q) unexpected error: %v", tc.input, err)
 			}
-			if got != tc.want {
+			if !reflect.DeepEqual(got, tc.want) {
 				t.Errorf("ParseStep(%q)\n  got  %+v\n  want %+v", tc.input, got, tc.want)
 			}
 		})

internal/sandbox/images.go

@@ -6,6 +6,8 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strconv"
+	"strings"
 
 	"git.omukk.dev/wrenn/wrenn/internal/id"
 	"git.omukk.dev/wrenn/wrenn/internal/layout"
@@ -66,6 +68,42 @@ func EnsureImageSizes(wrennDir string, targetMB int) error {
 	return nil
 }
 
+// ParseSizeToMB parses a human-readable size string into megabytes.
+// Supported suffixes: G, Gi (gibibytes), M, Mi (mebibytes).
+// Examples: "5G" → 5120, "2Gi" → 2048, "1000M" → 1000, "512Mi" → 512.
+func ParseSizeToMB(s string) (int, error) {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return 0, fmt.Errorf("empty size string")
+	}
+
+	// Find where the numeric part ends.
+	i := 0
+	for i < len(s) && (s[i] == '.' || (s[i] >= '0' && s[i] <= '9')) {
+		i++
+	}
+	if i == 0 {
+		return 0, fmt.Errorf("invalid size %q: no numeric value", s)
+	}
+
+	numStr := s[:i]
+	suffix := strings.TrimSpace(s[i:])
+
+	num, err := strconv.ParseFloat(numStr, 64)
+	if err != nil {
+		return 0, fmt.Errorf("invalid size %q: %w", s, err)
+	}
+
+	switch suffix {
+	case "G", "Gi":
+		return int(num * 1024), nil
+	case "M", "Mi", "":
+		return int(num), nil
+	default:
+		return 0, fmt.Errorf("invalid size %q: unknown suffix %q (use G, Gi, M, or Mi)", s, suffix)
+	}
+}
+
 // expandImage expands a single rootfs image if it is smaller than targetBytes.
 func expandImage(rootfs string, targetBytes int64, targetMB int) error {
 	info, err := os.Stat(rootfs)

internal/sandbox/manager.go

@@ -28,8 +28,9 @@ import (
 
 // Config holds the paths and defaults for the sandbox manager.
 type Config struct {
-	WrennDir    string // root directory (e.g. /var/lib/wrenn); all sub-paths derived via layout package
-	EnvdTimeout time.Duration
+	WrennDir           string // root directory (e.g. /var/lib/wrenn); all sub-paths derived via layout package
+	EnvdTimeout        time.Duration
+	DefaultRootfsSizeMB int // target size for template rootfs images; 0 → DefaultDiskSizeMB
 }
 
 // Manager orchestrates sandbox lifecycle: VM, network, filesystem, envd.
@@ -924,8 +925,8 @@ func (m *Manager) FlattenRootfs(ctx context.Context, sandboxID string, teamID, t
 	// Clean up dm device and loop device now that flatten is complete.
 	m.cleanupDM(sb)
 
-	// Shrink the flattened image to its minimum size so stored templates are
-	// compact. EnsureImageSizes will re-expand them on the next agent startup.
+	// Shrink the flattened image to its minimum size, then re-expand to the
+	// configured default rootfs size so sandboxes see the full disk from boot.
 	if out, err := exec.Command("e2fsck", "-fy", outputPath).CombinedOutput(); err != nil {
 		if exitErr, ok := err.(*exec.ExitError); ok && exitErr.ExitCode() > 1 {
 			slog.Warn("e2fsck before shrink failed (non-fatal)", "output", string(out), "error", err)
@@ -935,6 +936,15 @@ func (m *Manager) FlattenRootfs(ctx context.Context, sandboxID string, teamID, t
 		slog.Warn("resize2fs -M failed (non-fatal)", "output", string(out), "error", err)
 	}
 
+	// Re-expand to default rootfs size.
+	targetMB := m.cfg.DefaultRootfsSizeMB
+	if targetMB <= 0 {
+		targetMB = DefaultDiskSizeMB
+	}
+	if err := expandImage(outputPath, int64(targetMB)*1024*1024, targetMB); err != nil {
+		slog.Warn("failed to expand template to default size (non-fatal)", "error", err)
+	}
+
 	sizeBytes, err := snapshot.DirSize(flattenDstDir, "")
 	if err != nil {
 		slog.Warn("failed to calculate template size", "error", err)

internal/service/build.go

@@ -31,6 +31,7 @@ const (
 var preBuildCmds = []string{
 	"RUN apt update",
 	"USER wrenn-user",
+	"WORKDIR /home/wrenn-user",
 }
 
 // postBuildCmds run after the user recipe to clean up caches and reduce image size.
@@ -725,11 +726,13 @@ func (s *BuildService) uploadAndExtractArchive(
 		return fmt.Errorf("write archive: %w", err)
 	}
 
-	// Extract.
+	// Extract and ensure files are readable.
+	fullCmd := extractCmd + " && chmod -R a+rX /tmp/build-files"
+
 	resp, err := agent.Exec(ctx, connect.NewRequest(&pb.ExecRequest{
 		SandboxId:  sandboxID,
 		Cmd:        "/bin/sh",
-		Args:       []string{"-c", extractCmd},
+		Args:       []string{"-c", fullCmd},
 		TimeoutSec: 120,
 	}))
 	if err != nil {