Add godoc strings to all exported types, functions, and fields

Documents:
- cli: NO_COLOR, RunOptions fields, CLIApp, VersionString
- checker: Result fields, Status constants, CheckStatus fields
- scanner: EnumerateStatus, ScanStatus, Options, FileEntry fields
- log: Level alias, DisableStyling, Init, Info/Debug functions,
  verbosity helpers, GetLogger, GetLevel, WithError
- mfer: ManifestScanOptions, New, NewFromPaths, NewFromFS, MAGIC

internal/checker/checker.go

@@ -16,21 +16,21 @@ import (
 
 // Result represents the outcome of checking a single file.
 type Result struct {
-	Path    string
-	Status  Status
-	Message string
+	Path    string // Relative path from manifest
+	Status  Status // Verification result status
+	Message string // Human-readable description of the result
 }
 
 // Status represents the verification status of a file.
 type Status int
 
 const (
-	StatusOK Status = iota
-	StatusMissing
-	StatusSizeMismatch
-	StatusHashMismatch
-	StatusExtra // File exists on disk but not in manifest
-	StatusError
+	StatusOK           Status = iota // File matches manifest (size and hash verified)
+	StatusMissing                    // File not found on disk
+	StatusSizeMismatch               // File size differs from manifest
+	StatusHashMismatch               // File hash differs from manifest
+	StatusExtra                      // File exists on disk but not in manifest
+	StatusError                      // Error occurred during verification
 )
 
 func (s Status) String() string {
@@ -54,12 +54,12 @@ func (s Status) String() string {
 
 // CheckStatus contains progress information for the check operation.
 type CheckStatus struct {
-	TotalFiles   int64
-	CheckedFiles int64
-	TotalBytes   int64
-	CheckedBytes int64
-	BytesPerSec  float64
-	Failures     int64
+	TotalFiles   int64   // Total number of files in manifest
+	CheckedFiles int64   // Number of files checked so far
+	TotalBytes   int64   // Total bytes to verify (sum of all file sizes)
+	CheckedBytes int64   // Bytes verified so far
+	BytesPerSec  float64 // Current throughput rate
+	Failures     int64   // Number of verification failures encountered
 }
 
 // Checker verifies files against a manifest.

internal/cli/entry.go

@@ -7,6 +7,8 @@ import (
 	"github.com/spf13/afero"
 )
 
+// NO_COLOR disables colored output when set. Automatically true if the
+// NO_COLOR environment variable is present (per https://no-color.org/).
 var NO_COLOR bool
 
 func init() {
@@ -17,15 +19,16 @@ func init() {
 }
 
 // RunOptions contains all configuration for running the CLI application.
+// Use DefaultRunOptions for standard CLI execution, or construct manually for testing.
 type RunOptions struct {
-	Appname string
-	Version string
-	Gitrev  string
-	Args    []string
-	Stdin   io.Reader
-	Stdout  io.Writer
-	Stderr  io.Writer
-	Fs      afero.Fs
+	Appname string    // Application name displayed in help and version output
+	Version string    // Version string (typically set at build time)
+	Gitrev  string    // Git revision hash (typically set at build time)
+	Args    []string  // Command-line arguments (typically os.Args)
+	Stdin   io.Reader // Standard input stream
+	Stdout  io.Writer // Standard output stream
+	Stderr  io.Writer // Standard error stream
+	Fs      afero.Fs  // Filesystem abstraction for file operations
 }
 
 // DefaultRunOptions returns RunOptions configured for normal CLI execution.

internal/cli/mfer.go

@@ -11,6 +11,8 @@ import (
 	"sneak.berlin/go/mfer/internal/log"
 )
 
+// CLIApp is the main CLI application container. It holds configuration,
+// I/O streams, and filesystem abstraction to enable testing and flexibility.
 type CLIApp struct {
 	appname     string
 	version     string
@@ -19,13 +21,10 @@ type CLIApp struct {
 	exitCode    int
 	app         *cli.App
 
-	// I/O streams - all program input/output should go through these
-	Stdin  io.Reader
-	Stdout io.Writer
-	Stderr io.Writer
-
-	// Fs is the filesystem abstraction - defaults to OsFs for real filesystem
-	Fs afero.Fs
+	Stdin  io.Reader // Standard input stream
+	Stdout io.Writer // Standard output stream for normal output
+	Stderr io.Writer // Standard error stream for diagnostics
+	Fs     afero.Fs  // Filesystem abstraction for all file operations
 }
 
 const banner = `
@@ -45,6 +44,7 @@ func (mfa *CLIApp) printBanner() {
 	fmt.Fprintln(mfa.Stdout, banner)
 }
 
+// VersionString returns the version and git revision formatted for display.
 func (mfa *CLIApp) VersionString() string {
 	return fmt.Sprintf("%s (%s)", mfa.version, mfa.gitrev)
 }

internal/log/log.go

@@ -13,6 +13,7 @@ import (
 	"github.com/pterm/pterm"
 )
 
+// Level is an alias for apex/log.Level for use by callers without importing apex/log.
 type Level = log.Level
 
 var (
@@ -48,6 +49,7 @@ func GetStderr() io.Writer {
 	return stderr
 }
 
+// DisableStyling turns off colors and styling for terminal output.
 func DisableStyling() {
 	pterm.DisableColor()
 	pterm.DisableStyling()
@@ -59,6 +61,7 @@ func DisableStyling() {
 	pterm.Fatal.Prefix.Text = ""
 }
 
+// Init initializes the logger with the CLI handler and default log level.
 func Init() {
 	mu.RLock()
 	w := stderr
@@ -67,22 +70,27 @@ func Init() {
 	log.SetLevel(log.InfoLevel)
 }
 
+// Infof logs a formatted message at info level.
 func Infof(format string, args ...interface{}) {
 	log.Infof(format, args...)
 }
 
+// Info logs a message at info level.
 func Info(arg string) {
 	log.Info(arg)
 }
 
+// Debugf logs a formatted message at debug level with caller location.
 func Debugf(format string, args ...interface{}) {
 	DebugReal(fmt.Sprintf(format, args...), 2)
 }
 
+// Debug logs a message at debug level with caller location.
 func Debug(arg string) {
 	DebugReal(arg, 2)
 }
 
+// DebugReal logs at debug level with caller info from the specified stack depth.
 func DebugReal(arg string, cs int) {
 	_, callerFile, callerLine, ok := runtime.Caller(cs)
 	if !ok {
@@ -92,14 +100,18 @@ func DebugReal(arg string, cs int) {
 	log.Debug(tag + arg)
 }
 
+// Dump logs a spew dump of the arguments at debug level.
 func Dump(args ...interface{}) {
 	DebugReal(spew.Sdump(args...), 2)
 }
 
+// EnableDebugLogging sets the log level to debug.
 func EnableDebugLogging() {
 	SetLevel(log.DebugLevel)
 }
 
+// VerbosityStepsToLogLevel converts a -v count to a log level.
+// 0 returns InfoLevel, 1+ returns DebugLevel.
 func VerbosityStepsToLogLevel(l int) log.Level {
 	switch l {
 	case 0:
@@ -111,14 +123,17 @@ func VerbosityStepsToLogLevel(l int) log.Level {
 	return log.DebugLevel
 }
 
+// SetLevelFromVerbosity sets the log level based on -v flag count.
 func SetLevelFromVerbosity(l int) {
 	SetLevel(VerbosityStepsToLogLevel(l))
 }
 
+// SetLevel sets the global log level.
 func SetLevel(arg log.Level) {
 	log.SetLevel(arg)
 }
 
+// GetLogger returns the underlying apex/log Logger.
 func GetLogger() *log.Logger {
 	if logger, ok := log.Log.(*log.Logger); ok {
 		return logger
@@ -126,10 +141,12 @@ func GetLogger() *log.Logger {
 	panic("unable to get logger")
 }
 
+// GetLevel returns the current log level.
 func GetLevel() log.Level {
 	return GetLogger().Level
 }
 
+// WithError returns a log entry with the error attached.
 func WithError(e error) *log.Entry {
 	return GetLogger().WithError(e)
 }

internal/scanner/scanner.go

@@ -21,8 +21,8 @@ import (
 
 // EnumerateStatus contains progress information for the enumeration phase.
 type EnumerateStatus struct {
-	FilesFound int64
-	BytesFound int64
+	FilesFound int64 // Number of files discovered so far
+	BytesFound int64 // Total size of discovered files (from stat)
 }
 
 // Phase 2: Scan (ToManifest)
@@ -32,27 +32,27 @@ type EnumerateStatus struct {
 
 // ScanStatus contains progress information for the scan phase.
 type ScanStatus struct {
-	TotalFiles   int64
-	ScannedFiles int64
-	TotalBytes   int64
-	ScannedBytes int64
-	BytesPerSec  float64
+	TotalFiles   int64   // Total number of files to scan
+	ScannedFiles int64   // Number of files scanned so far
+	TotalBytes   int64   // Total bytes to read (sum of all file sizes)
+	ScannedBytes int64   // Bytes read so far
+	BytesPerSec  float64 // Current throughput rate
 }
 
 // Options configures scanner behavior.
 type Options struct {
-	IgnoreDotfiles bool
-	FollowSymLinks bool
-	Fs             afero.Fs // Filesystem to use, defaults to OsFs
+	IgnoreDotfiles bool     // Skip files and directories starting with a dot
+	FollowSymLinks bool     // Resolve symlinks instead of skipping them
+	Fs             afero.Fs // Filesystem to use, defaults to OsFs if nil
 }
 
 // FileEntry represents a file that has been enumerated.
 type FileEntry struct {
-	Path    string // Relative path (used in manifest)
-	AbsPath string // Absolute path (used for reading file content)
-	Size    int64
-	Mtime   time.Time
-	Ctime   time.Time
+	Path    string    // Relative path (used in manifest)
+	AbsPath string    // Absolute path (used for reading file content)
+	Size    int64     // File size in bytes
+	Mtime   time.Time // Last modification time
+	Ctime   time.Time // Creation time (platform-dependent)
 }
 
 // Scanner accumulates files and generates manifests from them.

mfer/manifest.go

@@ -39,9 +39,10 @@ func (m *manifest) String() string {
 	return fmt.Sprintf("<Manifest count=%d totalSize=%d>", len(m.files), m.totalFileSize)
 }
 
+// ManifestScanOptions configures behavior when scanning directories for manifest generation.
 type ManifestScanOptions struct {
-	IgnoreDotfiles bool
-	FollowSymLinks bool
+	IgnoreDotfiles bool // Skip files and directories starting with a dot
+	FollowSymLinks bool // Resolve symlinks instead of skipping them
 }
 
 func (m *manifest) HasError() bool {
@@ -77,11 +78,13 @@ func (m *manifest) addInputFS(f afero.Fs) error {
 	return nil
 }
 
+// New creates an empty manifest.
 func New() *manifest {
 	m := &manifest{}
 	return m
 }
 
+// NewFromPaths creates a manifest configured to scan the given filesystem paths.
 func NewFromPaths(options *ManifestScanOptions, inputPaths ...string) (*manifest, error) {
 	log.Dump(inputPaths)
 	m := New()
@@ -95,6 +98,7 @@ func NewFromPaths(options *ManifestScanOptions, inputPaths ...string) (*manifest
 	return m, nil
 }
 
+// NewFromFS creates a manifest configured to scan the given afero filesystem.
 func NewFromFS(options *ManifestScanOptions, fs afero.Fs) (*manifest, error) {
 	m := New()
 	m.scanOptions = options

mfer/serialize.go

@@ -10,9 +10,7 @@ import (
 	"google.golang.org/protobuf/proto"
 )
 
-// was go-generate protoc --go_out=. --go_opt=paths=source_relative mf.proto
-
-// rot13("MANIFEST")
+// MAGIC is the file format magic bytes prefix (rot13 of "MANIFEST").
 const MAGIC string = "ZNAVSRFG"
 
 func newTimestampFromTime(t time.Time) *Timestamp {