fix(sandbox): classify helper-tool errors with usefulerror (#272)

* fix(sandbox): classify helper-tool errors with usefulerror

Sandbox helper commands (profile lint/diff/show/init/list) used to bubble
up plain fmt.Errorf chains from the registry layer, which the TUI then
classified as Unknown and decorated with a bug-report link. Wrap each
error path at the cmd/sandbox boundary so the TUI prints NotFound,
InvalidArgument, or PermissionDenied with actionable hints instead.

Closes #269

* refactor(sandbox): classify registry errors via sentinel wrapping

Replace the fragile substring match in profileLoadError with errors.Is
against new sandbox.ErrProfileNotFound / sandbox.ErrProfileInvalid
sentinels. Every fmt.Errorf in registry.go that previously communicated
"missing" or "malformed" by message text now wraps the corresponding
sentinel, so the cmd layer can classify without inspecting strings.

* fix(sandbox): detect IO error class when wrapping helper errors

Replace static ErrCodeUnknown / ErrCodePermissionDenied wrappings with
ioErrorCode, which inspects the error chain for fs.ErrPermission and
fs.ErrNotExist before falling back. Applied to runProfileList (where an
unreadable user profile directory now classifies as PermissionDenied),
registryInitError, and the stat/MkdirAll/WriteFile paths in profile init.

Also drop redundant doc comments on helpers whose names are self-evident.

---------

Co-authored-by: Claude <noreply@anthropic.com>

cmd/sandbox/helpers.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"regexp"
 	"strings"
 
@@ -62,6 +63,56 @@ func notFoundError(message, help string) error {
 		Wrap(errors.New(message))
 }
 
+// Idempotent: returns err unchanged when nil or already useful, so call
+// sites can apply it without losing more precise pre-classified errors.
+func wrapUseful(err error, code, help string) error {
+	if err == nil {
+		return nil
+	}
+	if _, ok := usefulerror.AsUsefulError(err); ok {
+		return err
+	}
+	return usefulerror.Useful().
+		WithCode(code).
+		WithHumanError(err.Error()).
+		WithHelp(help).
+		Wrap(err)
+}
+
+func profileLoadError(err error) error {
+	if err == nil {
+		return nil
+	}
+	if _, ok := usefulerror.AsUsefulError(err); ok {
+		return err
+	}
+	switch {
+	case errors.Is(err, pmgsandbox.ErrProfileNotFound):
+		return wrapUseful(err, usefulerror.ErrCodeNotFound,
+			"Use `pmg sandbox profile list` to see available profiles, or pass an existing profile YAML path.")
+	case errors.Is(err, pmgsandbox.ErrProfileInvalid):
+		return wrapUseful(err, usefulerror.ErrCodeInvalidArgument,
+			"Check the profile YAML for syntax/schema issues and verify any 'inherits:' parent name.")
+	}
+	return wrapUseful(err, usefulerror.ErrCodeUnknown,
+		"Failed to load the sandbox profile. Run with --verbose for the underlying cause.")
+}
+
+func registryInitError(err error) error {
+	return wrapUseful(err, ioErrorCode(err, usefulerror.ErrCodeUnknown),
+		"Failed to initialise the sandbox profile registry. Run with --verbose for details.")
+}
+
+func ioErrorCode(err error, fallback string) string {
+	switch {
+	case errors.Is(err, fs.ErrPermission):
+		return usefulerror.ErrCodePermissionDenied
+	case errors.Is(err, fs.ErrNotExist):
+		return usefulerror.ErrCodeNotFound
+	}
+	return fallback
+}
+
 func writeJSONIndent(out io.Writer, v any) error {
 	enc := json.NewEncoder(out)
 	enc.SetIndent("", "  ")

cmd/sandbox/profile_diff.go

@@ -9,6 +9,7 @@ import (
 	"github.com/pmezard/go-difflib/difflib"
 	pmgsandbox "github.com/safedep/pmg/sandbox"
 	"github.com/safedep/pmg/sandbox/platform"
+	"github.com/safedep/pmg/usefulerror"
 	"github.com/spf13/cobra"
 	"gopkg.in/yaml.v3"
 )
@@ -68,7 +69,7 @@ func runProfileDiff(out io.Writer, errOut io.Writer, nameA, nameB string, opts *
 
 	registry, err := factory()
 	if err != nil {
-		return &diffOpError{err: err}
+		return &diffOpError{err: registryInitError(err)}
 	}
 
 	dataA, err := materialize(registry, nameA, opts)
@@ -82,7 +83,8 @@ func runProfileDiff(out io.Writer, errOut io.Writer, nameA, nameB string, opts *
 
 	if bytes.Equal(dataA, dataB) {
 		if _, err := fmt.Fprintln(errOut, "profiles are identical"); err != nil {
-			return &diffOpError{err: err}
+			return &diffOpError{err: wrapUseful(err, usefulerror.ErrCodeUnknown,
+				"Failed to write diff output. Check that stderr is writable.")}
 		}
 		return nil
 	}
@@ -96,16 +98,20 @@ func runProfileDiff(out io.Writer, errOut io.Writer, nameA, nameB string, opts *
 	}
 	text, err := difflib.GetUnifiedDiffString(diff)
 	if err != nil {
-		return &diffOpError{err: fmt.Errorf("failed to render diff: %w", err)}
+		return &diffOpError{err: wrapUseful(fmt.Errorf("failed to render diff: %w", err),
+			usefulerror.ErrCodeUnknown,
+			"Could not render the unified diff. Re-run with --verbose for the underlying cause.")}
 	}
 
 	if _, err := io.WriteString(out, text); err != nil {
-		return &diffOpError{err: err}
+		return &diffOpError{err: wrapUseful(err, usefulerror.ErrCodeUnknown,
+			"Failed to write diff output. Check that stdout is writable.")}
 	}
 
 	if !strings.HasSuffix(text, "\n") {
 		if _, err := fmt.Fprintln(out); err != nil {
-			return &diffOpError{err: err}
+			return &diffOpError{err: wrapUseful(err, usefulerror.ErrCodeUnknown,
+				"Failed to write diff output. Check that stdout is writable.")}
 		}
 	}
 
@@ -118,11 +124,16 @@ func materialize(registry pmgsandbox.ProfileRegistry, name string, opts *profile
 		Home: opts.home,
 	})
 	if err != nil {
-		return nil, err
+		return nil, profileLoadError(err)
 	}
 
 	if opts.driver != "" {
-		return platform.Render(pmgsandbox.DriverName(opts.driver), policy)
+		rendered, err := platform.Render(pmgsandbox.DriverName(opts.driver), policy)
+		if err != nil {
+			return nil, wrapUseful(err, usefulerror.ErrCodeInvalidArgument,
+				"Could not render the policy for the requested driver. Verify the driver is supported on this host.")
+		}
+		return rendered, nil
 	}
 
 	// Strip inherits since both sides are post-resolution.
@@ -130,7 +141,9 @@ func materialize(registry pmgsandbox.ProfileRegistry, name string, opts *profile
 
 	data, err := yaml.Marshal(policy)
 	if err != nil {
-		return nil, fmt.Errorf("failed to marshal resolved policy %s: %w", name, err)
+		return nil, wrapUseful(fmt.Errorf("failed to marshal resolved policy %s: %w", name, err),
+			usefulerror.ErrCodeUnknown,
+			"Failed to marshal the resolved policy to YAML. Re-run with --verbose for the underlying cause.")
 	}
 	return data, nil
 }

cmd/sandbox/profile_diff_test.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/safedep/pmg/usefulerror"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -96,6 +97,9 @@ func TestProfileDiffUnknownProfile(t *testing.T) {
 	assert.Empty(t, stdout)
 	assert.Empty(t, stderr)
 	assert.Contains(t, err.Error(), "no-such-profile-xyz")
+	usefulErr, ok := usefulerror.AsUsefulError(err)
+	require.True(t, ok, "diff error should expose a UsefulError through Unwrap")
+	assert.Equal(t, usefulerror.ErrCodeNotFound, usefulErr.Code())
 }
 
 func TestProfileDiffUnknownDriver(t *testing.T) {
@@ -107,6 +111,9 @@ func TestProfileDiffUnknownDriver(t *testing.T) {
 	assert.Empty(t, stdout)
 	assert.Empty(t, stderr)
 	assert.Contains(t, err.Error(), "unknown driver")
+	usefulErr, ok := usefulerror.AsUsefulError(err)
+	require.True(t, ok, "diff error should expose a UsefulError through Unwrap")
+	assert.Equal(t, usefulerror.ErrCodeInvalidArgument, usefulErr.Code())
 }
 
 func TestProfileDiffMissingProfileShowsUsage(t *testing.T) {

cmd/sandbox/profile_init.go

@@ -8,6 +8,7 @@ import (
 	"regexp"
 	"strings"
 
+	"github.com/safedep/pmg/usefulerror"
 	"github.com/spf13/cobra"
 )
 
@@ -59,7 +60,7 @@ func runProfileInit(out io.Writer, name string, opts *profileInitOptions, factor
 
 	registry, err := factory()
 	if err != nil {
-		return err
+		return registryInitError(err)
 	}
 
 	userDir := registry.UserProfileDir()
@@ -93,17 +94,23 @@ func runProfileInit(out io.Writer, name string, opts *profileInitOptions, factor
 			"Choose a different profile name, or edit the existing profile file to merge changes.",
 		)
 	} else if !os.IsNotExist(err) {
-		return fmt.Errorf("failed to stat %s: %w", target, err)
+		return wrapUseful(fmt.Errorf("failed to stat %s: %w", target, err),
+			ioErrorCode(err, usefulerror.ErrCodeUnknown),
+			"Could not stat the target profile path. Check the user profile directory permissions.")
 	}
 
 	if err := os.MkdirAll(userDir, 0o755); err != nil {
-		return fmt.Errorf("failed to create user profile directory %s: %w", userDir, err)
+		return wrapUseful(fmt.Errorf("failed to create user profile directory %s: %w", userDir, err),
+			ioErrorCode(err, usefulerror.ErrCodePermissionDenied),
+			"Could not create the user profile directory. Check filesystem permissions for "+userDir+".")
 	}
 
 	content := renderScaffold(name, opts.description, opts.from, pms, placeholderPM)
 
 	if err := os.WriteFile(target, []byte(content), 0o644); err != nil {
-		return fmt.Errorf("failed to write %s: %w", target, err)
+		return wrapUseful(fmt.Errorf("failed to write %s: %w", target, err),
+			ioErrorCode(err, usefulerror.ErrCodePermissionDenied),
+			"Could not write the scaffolded profile. Check filesystem permissions for "+target+".")
 	}
 
 	_, err = fmt.Fprintln(out, target)

cmd/sandbox/profile_lint.go

@@ -56,12 +56,12 @@ func (e *lintFailError) ExitCode() int { return ExitCodeLintFail }
 func runProfileLint(out io.Writer, name string, opts *profileLintOptions, factory registryFactory) error {
 	registry, err := factory()
 	if err != nil {
-		return err
+		return registryInitError(err)
 	}
 
 	policy, resolvedName, err := resolveProfileForLint(name, registry)
 	if err != nil {
-		return err
+		return profileLoadError(err)
 	}
 
 	issues := pmgsandbox.LintProfile(policy)
@@ -89,7 +89,7 @@ func resolveProfileForLint(name string, registry pmgsandbox.ProfileRegistry) (*p
 	if _, ok := registry.BuiltinProfileYAML(name); ok {
 		policy, err := registry.GetProfile(name)
 		if err != nil {
-			return nil, "", err
+			return nil, "", profileLoadError(err)
 		}
 		return policy, name, nil
 	}
@@ -102,7 +102,7 @@ func resolveProfileForLint(name string, registry pmgsandbox.ProfileRegistry) (*p
 		if s.Source == pmgsandbox.ProfileSourceUser && s.Name == name {
 			policy, loadErr := registry.LoadCustomProfile(s.Path)
 			if loadErr != nil {
-				return nil, "", loadErr
+				return nil, "", profileLoadError(loadErr)
 			}
 			return policy, s.Path, nil
 		}
@@ -111,7 +111,7 @@ func resolveProfileForLint(name string, registry pmgsandbox.ProfileRegistry) (*p
 	if _, statErr := os.Stat(name); statErr == nil {
 		policy, loadErr := registry.LoadCustomProfile(name)
 		if loadErr != nil {
-			return nil, "", loadErr
+			return nil, "", profileLoadError(loadErr)
 		}
 		return policy, name, nil
 	}

cmd/sandbox/profile_lint_test.go

@@ -196,6 +196,24 @@ func TestProfileLintMissingTargetShowsUsage(t *testing.T) {
 	assert.Contains(t, stdout.String(), "pmg sandbox profile lint npm-restrictive")
 }
 
+func TestProfileLint_InvalidYAMLReturnsInvalidArgument(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "broken.yml")
+	require.NoError(t, os.WriteFile(path, []byte("name: broken\npackage_managers:\n  - npm\n  invalid: : :\n"), 0o644))
+
+	cmd := newProfileLintCommand(newTestRegistry(t, dir))
+	var stdout, stderr bytes.Buffer
+	cmd.SetOut(&stdout)
+	cmd.SetErr(&stderr)
+	cmd.SetArgs([]string{"broken"})
+
+	err := cmd.Execute()
+	require.Error(t, err)
+	usefulErr, ok := usefulerror.AsUsefulError(err)
+	require.True(t, ok)
+	assert.Equal(t, usefulerror.ErrCodeInvalidArgument, usefulErr.Code())
+}
+
 func TestProfileLint_LiteralPath(t *testing.T) {
 	dir := t.TempDir()
 	path := writeUserProfileLint(t, dir, "literal", `name: literal

cmd/sandbox/profile_list.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/safedep/pmg/internal/ui"
 	pmgsandbox "github.com/safedep/pmg/sandbox"
+	"github.com/safedep/pmg/usefulerror"
 	"github.com/spf13/cobra"
 )
 
@@ -39,12 +40,13 @@ func newProfileListCommand(factory registryFactory) *cobra.Command {
 func runProfileList(out io.Writer, opts *profileListOptions, factory registryFactory) error {
 	registry, err := factory()
 	if err != nil {
-		return err
+		return registryInitError(err)
 	}
 
 	summaries, err := registry.ListProfiles()
 	if err != nil {
-		return err
+		return wrapUseful(err, ioErrorCode(err, usefulerror.ErrCodeUnknown),
+			"Failed to enumerate sandbox profiles. Check the user profile directory permissions.")
 	}
 
 	if opts.jsonOut {

cmd/sandbox/profile_list_test.go

@@ -3,6 +3,9 @@ package sandbox
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
+	"fmt"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"testing"
@@ -11,6 +14,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	pmgsandbox "github.com/safedep/pmg/sandbox"
+	"github.com/safedep/pmg/usefulerror"
 )
 
 func newTestRegistry(t *testing.T, userDir string) registryFactory {
@@ -100,6 +104,43 @@ func TestProfileListShadowedTag(t *testing.T) {
 	assert.Contains(t, stdout.String(), "SHADOWED")
 }
 
+func TestProfileListRegistryFailureReturnsUseful(t *testing.T) {
+	factory := func() (pmgsandbox.ProfileRegistry, error) {
+		return nil, errors.New("boom")
+	}
+
+	cmd := newProfileListCommand(factory)
+	var stdout, stderr bytes.Buffer
+	cmd.SetOut(&stdout)
+	cmd.SetErr(&stderr)
+	cmd.SetArgs([]string{})
+
+	err := cmd.Execute()
+	require.Error(t, err)
+	usefulErr, ok := usefulerror.AsUsefulError(err)
+	require.True(t, ok)
+	assert.Equal(t, usefulerror.ErrCodeUnknown, usefulErr.Code())
+	assert.Contains(t, err.Error(), "boom")
+}
+
+func TestProfileListRegistryPermissionErrorReturnsPermissionDenied(t *testing.T) {
+	factory := func() (pmgsandbox.ProfileRegistry, error) {
+		return nil, fmt.Errorf("read dir: %w", fs.ErrPermission)
+	}
+
+	cmd := newProfileListCommand(factory)
+	var stdout, stderr bytes.Buffer
+	cmd.SetOut(&stdout)
+	cmd.SetErr(&stderr)
+	cmd.SetArgs([]string{})
+
+	err := cmd.Execute()
+	require.Error(t, err)
+	usefulErr, ok := usefulerror.AsUsefulError(err)
+	require.True(t, ok)
+	assert.Equal(t, usefulerror.ErrCodePermissionDenied, usefulErr.Code())
+}
+
 func TestProfileListRejectsUnexpectedArgs(t *testing.T) {
 	cmd := newProfileListCommand(newTestRegistry(t, ""))
 	var stdout, stderr bytes.Buffer

cmd/sandbox/profile_show.go

@@ -8,6 +8,7 @@ import (
 	"github.com/safedep/dry/log"
 	pmgsandbox "github.com/safedep/pmg/sandbox"
 	"github.com/safedep/pmg/sandbox/platform"
+	"github.com/safedep/pmg/usefulerror"
 	"github.com/spf13/cobra"
 	"gopkg.in/yaml.v3"
 )
@@ -53,7 +54,7 @@ func runProfileShow(out io.Writer, name string, opts *profileShowOptions, factor
 
 	registry, err := factory()
 	if err != nil {
-		return err
+		return registryInitError(err)
 	}
 
 	if opts.driver != "" {
@@ -70,7 +71,7 @@ func runProfileShow(out io.Writer, name string, opts *profileShowOptions, factor
 func runProfileShowRaw(out io.Writer, name string, opts *profileShowOptions, registry pmgsandbox.ProfileRegistry) error {
 	source, path, data, err := loadProfileSource(name, registry)
 	if err != nil {
-		return err
+		return profileLoadError(err)
 	}
 
 	if opts.jsonOut {
@@ -93,7 +94,7 @@ func runProfileShowResolved(out io.Writer, name string, opts *profileShowOptions
 		Home: opts.home,
 	})
 	if err != nil {
-		return err
+		return profileLoadError(err)
 	}
 
 	if opts.jsonOut {
@@ -106,7 +107,9 @@ func runProfileShowResolved(out io.Writer, name string, opts *profileShowOptions
 
 	data, err := yaml.Marshal(policy)
 	if err != nil {
-		return fmt.Errorf("failed to marshal resolved policy: %w", err)
+		return wrapUseful(fmt.Errorf("failed to marshal resolved policy: %w", err),
+			usefulerror.ErrCodeUnknown,
+			"Failed to marshal the resolved policy to YAML. Re-run with --verbose for the underlying cause.")
 	}
 
 	_, err = out.Write(data)
@@ -119,12 +122,13 @@ func runProfileShowDriver(out io.Writer, name string, opts *profileShowOptions,
 		Home: opts.home,
 	})
 	if err != nil {
-		return err
+		return profileLoadError(err)
 	}
 
 	rendered, err := platform.Render(pmgsandbox.DriverName(opts.driver), policy)
 	if err != nil {
-		return err
+		return wrapUseful(err, usefulerror.ErrCodeInvalidArgument,
+			"Could not render the policy for the requested driver. Verify the driver is supported on this host.")
 	}
 
 	if opts.jsonOut {

cmd/sandbox/profile_show_test.go

@@ -148,4 +148,7 @@ func TestProfileShowDriverNonNativeErrors(t *testing.T) {
 	require.Error(t, err)
 	assert.Empty(t, stderr.String())
 	assert.Contains(t, err.Error(), "not available")
+	usefulErr, ok := usefulerror.AsUsefulError(err)
+	require.True(t, ok, "non-native driver error should be reported as a UsefulError")
+	assert.Equal(t, usefulerror.ErrCodeInvalidArgument, usefulErr.Code())
 }