workspace: drop --readonly flag — advisory only against root guests

--readonly ran `chmod -R a-w` over the workspace after copying, but
every banger guest boots as root, and root bypasses DAC mode checks.
So a user running `vm workspace prepare ... --readonly` got the
mode bits set to 0444 but `echo x >> file` in the guest still
succeeded. The flag promised enforcement it couldn't deliver.

The feature also doesn't match the product model: workspaces are
prepared precisely so the guest CAN edit them, and `workspace
export` exists to pull those edits back as a patch. A
"read-only workspace" contradicts that loop.

Removed:
  - CLI flag `--readonly` on `vm workspace prepare`
  - api.VMWorkspacePrepareParams.ReadOnly field
  - model.WorkspacePrepareResult.ReadOnly field
  - daemon chmod dispatch in prepareVMWorkspaceGuestIO
  - smoke scenario pinning the (advisory) mode-bit behavior
  - misleading "exportbox-readonly" VM name in an unrelated export
    test (the test is about not mutating the real git index;
    renamed to exportbox-noindex-mutation)

If real enforcement becomes a user need later, the right primitive
is `chattr +i` (immutable bit — root CAN'T write) or a ro bind-mount.
Reintroducing a new flag is cheaper than debugging what the current
one actually guarantees.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/api/types.go

@@ -143,7 +143,6 @@ type VMWorkspacePrepareParams struct {
 	Branch           string `json:"branch,omitempty"`
 	From             string `json:"from,omitempty"`
 	Mode             string `json:"mode,omitempty"`
-	ReadOnly         bool   `json:"readonly,omitempty"`
 	IncludeUntracked bool   `json:"include_untracked,omitempty"`
 }
 

internal/cli/commands_vm.go

@@ -583,7 +583,6 @@ func (d *deps) newVMWorkspacePrepareCommand() *cobra.Command {
 	var branchName string
 	var fromRef string
 	var mode string
-	var readOnly bool
 	var includeUntracked bool
 	var dryRun bool
 	cmd := &cobra.Command{
@@ -594,7 +593,7 @@ func (d *deps) newVMWorkspacePrepareCommand() *cobra.Command {
 		ValidArgsFunction: d.completeVMNameOnlyAtPos0,
 		Example: strings.TrimSpace(`
   banger vm workspace prepare devbox
-  banger vm workspace prepare devbox ../repo --guest-path /root/repo --readonly
+  banger vm workspace prepare devbox ../repo --guest-path /root/repo
   banger vm workspace prepare devbox ../repo --mode full_copy
 `),
 		RunE: func(cmd *cobra.Command, args []string) error {
@@ -634,7 +633,6 @@ func (d *deps) newVMWorkspacePrepareCommand() *cobra.Command {
 				Branch:           branchName,
 				From:             prepareFrom,
 				Mode:             mode,
-				ReadOnly:         readOnly,
 				IncludeUntracked: includeUntracked,
 			})
 			if err != nil {
@@ -647,7 +645,6 @@ func (d *deps) newVMWorkspacePrepareCommand() *cobra.Command {
 	cmd.Flags().StringVar(&branchName, "branch", "", "create and switch to a new guest branch")
 	cmd.Flags().StringVar(&fromRef, "from", "HEAD", "base ref for --branch")
 	cmd.Flags().StringVar(&mode, "mode", string(model.WorkspacePrepareModeShallowOverlay), "workspace mode: shallow_overlay, full_copy, metadata_only")
-	cmd.Flags().BoolVar(&readOnly, "readonly", false, "make the prepared workspace read-only")
 	cmd.Flags().BoolVar(&includeUntracked, "include-untracked", false, "also copy untracked non-ignored files into the guest workspace (default: tracked files only)")
 	cmd.Flags().BoolVar(&dryRun, "dry-run", false, "list the files that would be copied and exit without touching the guest")
 	return cmd

internal/daemon/workspace.go

@@ -1,7 +1,6 @@
 package daemon
 
 import (
-	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -182,13 +181,13 @@ func (s *WorkspaceService) PrepareVMWorkspace(ctx context.Context, params api.VM
 	unlock := s.workspaceLocks.lock(vm.ID)
 	defer unlock()
 
-	return s.prepareVMWorkspaceGuestIO(ctx, vm, strings.TrimSpace(params.SourcePath), guestPath, branchName, fromRef, mode, params.ReadOnly, params.IncludeUntracked)
+	return s.prepareVMWorkspaceGuestIO(ctx, vm, strings.TrimSpace(params.SourcePath), guestPath, branchName, fromRef, mode, params.IncludeUntracked)
 }
 
 // prepareVMWorkspaceGuestIO performs the actual guest-side work:
-// inspect the local repo, dial SSH, stream the tar, optionally chmod
-// readonly. It is called without holding the VM mutex.
-func (s *WorkspaceService) prepareVMWorkspaceGuestIO(ctx context.Context, vm model.VMRecord, sourcePath, guestPath, branchName, fromRef string, mode model.WorkspacePrepareMode, readOnly, includeUntracked bool) (model.WorkspacePrepareResult, error) {
+// inspect the local repo, dial SSH, stream the tar. Called without
+// holding the VM mutex.
+func (s *WorkspaceService) prepareVMWorkspaceGuestIO(ctx context.Context, vm model.VMRecord, sourcePath, guestPath, branchName, fromRef string, mode model.WorkspacePrepareMode, includeUntracked bool) (model.WorkspacePrepareResult, error) {
 	spec, err := s.workspaceInspectRepoHook(ctx, sourcePath, branchName, fromRef, includeUntracked)
 	if err != nil {
 		return model.WorkspacePrepareResult{}, err
@@ -208,13 +207,6 @@ func (s *WorkspaceService) prepareVMWorkspaceGuestIO(ctx context.Context, vm mod
 	if err := s.workspaceImportHook(ctx, client, spec, guestPath, mode); err != nil {
 		return model.WorkspacePrepareResult{}, err
 	}
-	if readOnly {
-		var chmodLog bytes.Buffer
-		chmodScript := fmt.Sprintf("set -euo pipefail\nchmod -R a-w %s\n", ws.ShellQuote(guestPath))
-		if err := client.RunScript(ctx, chmodScript, &chmodLog); err != nil {
-			return model.WorkspacePrepareResult{}, ws.FormatStepError("set workspace readonly", err, chmodLog.String())
-		}
-	}
 	return model.WorkspacePrepareResult{
 		VMID:          vm.ID,
 		SourcePath:    spec.SourcePath,
@@ -222,7 +214,6 @@ func (s *WorkspaceService) prepareVMWorkspaceGuestIO(ctx context.Context, vm mod
 		RepoName:      spec.RepoName,
 		GuestPath:     guestPath,
 		Mode:          mode,
-		ReadOnly:      readOnly,
 		HeadCommit:    spec.HeadCommit,
 		CurrentBranch: spec.CurrentBranch,
 		BranchName:    spec.BranchName,

internal/daemon/workspace_test.go

@@ -555,7 +555,7 @@ func TestExportVMWorkspace_DoesNotMutateRealIndex(t *testing.T) {
 	apiSock := filepath.Join(t.TempDir(), "fc.sock")
 	firecracker := startFakeFirecracker(t, apiSock)
 
-	vm := testVM("exportbox-readonly", "image-export", "172.16.0.107")
+	vm := testVM("exportbox-noindex-mutation", "image-export", "172.16.0.107")
 	vm.State = model.VMStateRunning
 	vm.Runtime.State = model.VMStateRunning
 	vm.Runtime.APISockPath = apiSock

internal/model/types.go

@@ -172,7 +172,6 @@ type WorkspacePrepareResult struct {
 	RepoName      string               `json:"repo_name"`
 	GuestPath     string               `json:"guest_path"`
 	Mode          WorkspacePrepareMode `json:"mode"`
-	ReadOnly      bool                 `json:"readonly"`
 	HeadCommit    string               `json:"head_commit,omitempty"`
 	CurrentBranch string               `json:"current_branch,omitempty"`
 	BranchName    string               `json:"branch_name,omitempty"`