fix(log): inherit nested error codes

Co-Authored-By: Virgil <virgil@lethean.io>

docs/architecture.md

@@ -63,6 +63,9 @@ type Err struct {
     Msg  string // human-readable description
     Err  error  // underlying cause (optional)
     Code string // machine-readable code (optional, e.g. "VALIDATION_FAILED")
+    Retryable  bool          // whether the caller can retry the operation
+    RetryAfter *time.Duration // optional retry delay hint
+    NextAction string        // suggested next step when not retryable
 }
 ```
 
@@ -115,6 +118,9 @@ log(LevelInfo, "[INF]", ...)
   |     if any value implements `error`:
   |       extract Op  -> append "op"    key if not already present
   |       extract FormatStackTrace -> append "stack" key if not already present
+  |       extract recovery hints -> append "retryable",
+  |                                 "retry_after_seconds",
+  |                                 "next_action" if not already present
   +-- format key-value pairs:
   |     string values -> %q (quoted, injection-safe)
   |     other values  -> %v

docs/index.md

@@ -5,7 +5,7 @@ description: Structured logging and error handling for Core applications
 
 # go-log
 
-`forge.lthn.ai/core/go-log` provides structured logging and contextual error
+`dappco.re/go/core/log` provides structured logging and contextual error
 handling for Go applications built on the Core framework.  It is a small,
 zero-dependency library (only `testify` at test time) that replaces ad-hoc
 `fmt.Println` / `log.Printf` calls with level-filtered, key-value structured
@@ -15,7 +15,7 @@ stack.
 ## Quick Start
 
 ```go
-import "forge.lthn.ai/core/go-log"
+import "dappco.re/go/core/log"
 
 // Use the package-level default logger straight away
 log.SetLevel(log.LevelDebug)
@@ -54,6 +54,10 @@ log.Op(err)             // "user.Save"
 log.Root(err)           // the original underlyingErr
 log.StackTrace(err)     // ["user.Save", "db.Connect"]
 log.FormatStackTrace(err) // "user.Save -> db.Connect"
+
+// Recovery hints are also available when the error carries them
+log.IsRetryable(err)    // false unless a wrapped Err marks it retryable
+log.RecoveryAction(err) // "retry with backoff" when provided
 ```
 
 ### Combined Log-and-Return
@@ -70,7 +74,7 @@ if err != nil {
 | File | Purpose |
 |------|---------|
 | `log.go` | Logger type, log levels, key-value formatting, redaction, default logger, `Username()` helper |
-| `errors.go` | `Err` structured error type, creation helpers (`E`, `Wrap`, `WrapCode`, `NewCode`), introspection (`Op`, `ErrCode`, `Root`, `StackTrace`), combined log-and-return helpers (`LogError`, `LogWarn`, `Must`) |
+| `errors.go` | `Err` structured error type, creation helpers (`E`, `Wrap`, `WrapCode`, `NewCode`, and recovery-aware variants), introspection (`Op`, `ErrCode`, `Root`, `StackTrace`, recovery hints), combined log-and-return helpers (`LogError`, `LogWarn`, `Must`) |
 | `log_test.go` | Tests for the Logger: level filtering, key-value output, redaction, injection prevention, security logging |
 | `errors_test.go` | Tests for structured errors: creation, wrapping, code propagation, introspection, stack traces, log-and-return helpers |
 
@@ -89,7 +93,7 @@ code.
 ## Module Path
 
 ```
-forge.lthn.ai/core/go-log
+dappco.re/go/core/log
 ```
 
 Requires **Go 1.26+** (uses `iter.Seq` from the standard library).

errors.go

@@ -7,9 +7,9 @@ package log
 
 import (
 	"errors"
-	"fmt"
 	"iter"
 	"strings"
+	"time"
 )
 
 // Err represents a structured error with operational context.
@@ -19,24 +19,44 @@ type Err struct {
 	Msg  string // Human-readable message
 	Err  error  // Underlying error (optional)
 	Code string // Error code (optional, e.g., "VALIDATION_FAILED")
+	// Retryable indicates whether the caller can safely retry this error.
+	Retryable bool
+	// RetryAfter suggests a delay before retrying when Retryable is true.
+	RetryAfter *time.Duration
+	// NextAction suggests an alternative path when this error is not directly retryable.
+	NextAction string
 }
 
 // Error implements the error interface.
 func (e *Err) Error() string {
-	var prefix string
+	if e == nil {
-	if e.Op != "" {
+		return ""
-		prefix = e.Op + ": "
 	}
-	if e.Err != nil {
+
+	body := e.Msg
+	if body == "" {
 		if e.Code != "" {
-			return fmt.Sprintf("%s%s [%s]: %v", prefix, e.Msg, e.Code, e.Err)
+			body = "[" + e.Code + "]"
 		}
-		return fmt.Sprintf("%s%s: %v", prefix, e.Msg, e.Err)
+	} else if e.Code != "" {
+		body += " [" + e.Code + "]"
 	}
-	if e.Code != "" {
+
-		return fmt.Sprintf("%s%s [%s]", prefix, e.Msg, e.Code)
+	if e.Err != nil {
+		if body != "" {
+			body += ": " + e.Err.Error()
+		} else {
+			body = e.Err.Error()
+		}
 	}
-	return fmt.Sprintf("%s%s", prefix, e.Msg)
+
+	if e.Op != "" {
+		if body != "" {
+			return e.Op + ": " + body
+		}
+		return e.Op
+	}
+	return body
 }
 
 // Unwrap returns the underlying error for use with errors.Is and errors.As.
@@ -57,6 +77,22 @@ func E(op, msg string, err error) error {
 	return &Err{Op: op, Msg: msg, Err: err}
 }
 
+// EWithRecovery creates a new Err with operation context and recovery metadata.
+//
+//	return log.EWithRecovery("api.Call", "temporary failure", err, true, &retryAfter, "retry with backoff")
+func EWithRecovery(op, msg string, err error, retryable bool, retryAfter *time.Duration, nextAction string) error {
+	recoveryErr := &Err{
+		Op:  op,
+		Msg: msg,
+		Err: err,
+	}
+	inheritRecovery(recoveryErr, err)
+	recoveryErr.Retryable = retryable
+	recoveryErr.RetryAfter = retryAfter
+	recoveryErr.NextAction = nextAction
+	return recoveryErr
+}
+
 // Wrap wraps an error with operation context.
 // Returns nil if err is nil, to support conditional wrapping.
 // Preserves error Code if the wrapped error is an *Err.
@@ -68,12 +104,29 @@ func Wrap(err error, op, msg string) error {
 	if err == nil {
 		return nil
 	}
-	// Preserve Code from wrapped *Err
+	wrapped := &Err{Op: op, Msg: msg, Err: err, Code: inheritedCode(err)}
-	var logErr *Err
+	inheritRecovery(wrapped, err)
-	if As(err, &logErr) && logErr.Code != "" {
+	return wrapped
-		return &Err{Op: op, Msg: msg, Err: err, Code: logErr.Code}
+}
+
+// WrapWithRecovery wraps an error with operation context and explicit recovery metadata.
+//
+//	return log.WrapWithRecovery(err, "api.Call", "temporary failure", true, &retryAfter, "retry with backoff")
+func WrapWithRecovery(err error, op, msg string, retryable bool, retryAfter *time.Duration, nextAction string) error {
+	if err == nil {
+		return nil
 	}
-	return &Err{Op: op, Msg: msg, Err: err}
+	recoveryErr := &Err{
+		Op:   op,
+		Msg:  msg,
+		Err:  err,
+		Code: ErrCode(err),
+	}
+	inheritRecovery(recoveryErr, err)
+	recoveryErr.Retryable = retryable
+	recoveryErr.RetryAfter = retryAfter
+	recoveryErr.NextAction = nextAction
+	return recoveryErr
 }
 
 // WrapCode wraps an error with operation context and error code.
@@ -87,7 +140,29 @@ func WrapCode(err error, code, op, msg string) error {
 	if err == nil && code == "" {
 		return nil
 	}
-	return &Err{Op: op, Msg: msg, Err: err, Code: code}
+	wrapped := &Err{Op: op, Msg: msg, Err: err, Code: code}
+	inheritRecovery(wrapped, err)
+	return wrapped
+}
+
+// WrapCodeWithRecovery wraps an error with operation context, code, and recovery metadata.
+//
+//	return log.WrapCodeWithRecovery(err, "TEMPORARY_UNAVAILABLE", "api.Call", "temporary failure", true, &retryAfter, "retry with backoff")
+func WrapCodeWithRecovery(err error, code, op, msg string, retryable bool, retryAfter *time.Duration, nextAction string) error {
+	if err == nil && code == "" {
+		return nil
+	}
+	recoveryErr := &Err{
+		Op:   op,
+		Msg:  msg,
+		Err:  err,
+		Code: code,
+	}
+	inheritRecovery(recoveryErr, err)
+	recoveryErr.Retryable = retryable
+	recoveryErr.RetryAfter = retryAfter
+	recoveryErr.NextAction = nextAction
+	return recoveryErr
 }
 
 // NewCode creates an error with just code and message (no underlying error).
@@ -100,28 +175,121 @@ func NewCode(code, msg string) error {
 	return &Err{Msg: msg, Code: code}
 }
 
+// NewCodeWithRecovery creates a coded error with recovery metadata.
+//
+//	var ErrTemporary = log.NewCodeWithRecovery("TEMPORARY_UNAVAILABLE", "temporary failure", true, &retryAfter, "retry with backoff")
+func NewCodeWithRecovery(code, msg string, retryable bool, retryAfter *time.Duration, nextAction string) error {
+	return &Err{
+		Msg:        msg,
+		Code:       code,
+		Retryable:  retryable,
+		RetryAfter: retryAfter,
+		NextAction: nextAction,
+	}
+}
+
+// inheritRecovery copies recovery metadata from the first *Err in err's chain.
+func inheritRecovery(dst *Err, err error) {
+	if err == nil || dst == nil {
+		return
+	}
+	var source *Err
+	if As(err, &source) {
+		dst.Retryable = source.Retryable
+		dst.RetryAfter = source.RetryAfter
+		dst.NextAction = source.NextAction
+	}
+}
+
+// inheritedCode returns the first non-empty code found in an error chain.
+func inheritedCode(err error) string {
+	for err != nil {
+		if wrapped, ok := err.(*Err); ok && wrapped.Code != "" {
+			return wrapped.Code
+		}
+		err = errors.Unwrap(err)
+	}
+	return ""
+}
+
+// RetryAfter returns the first retry-after hint from an error chain, if present.
+//
+//	retryAfter, ok := log.RetryAfter(err)
+func RetryAfter(err error) (*time.Duration, bool) {
+	for err != nil {
+		if wrapped, ok := err.(*Err); ok && wrapped.RetryAfter != nil {
+			return wrapped.RetryAfter, true
+		}
+		err = errors.Unwrap(err)
+	}
+	return nil, false
+}
+
+// IsRetryable reports whether the error chain contains a retryable Err.
+//
+//	if log.IsRetryable(err) { /* retry the operation */ }
+func IsRetryable(err error) bool {
+	var wrapped *Err
+	if As(err, &wrapped) {
+		return wrapped.Retryable
+	}
+	return false
+}
+
+// RecoveryAction returns the first next action from an error chain.
+//
+//	next := log.RecoveryAction(err)
+func RecoveryAction(err error) string {
+	for err != nil {
+		if wrapped, ok := err.(*Err); ok && wrapped.NextAction != "" {
+			return wrapped.NextAction
+		}
+		err = errors.Unwrap(err)
+	}
+	return ""
+}
+
+func retryableHint(err error) bool {
+	for err != nil {
+		if wrapped, ok := err.(*Err); ok && wrapped.Retryable {
+			return true
+		}
+		err = errors.Unwrap(err)
+	}
+	return false
+}
+
 // --- Standard Library Wrappers ---
 
 // Is reports whether any error in err's tree matches target.
 // Wrapper around errors.Is for convenience.
+//
+//	if log.Is(err, context.DeadlineExceeded) { /* handle timeout */ }
 func Is(err, target error) bool {
 	return errors.Is(err, target)
 }
 
 // As finds the first error in err's tree that matches target.
 // Wrapper around errors.As for convenience.
+//
+//	var e *log.Err
+//	if log.As(err, &e) { /* use e.Code */ }
 func As(err error, target any) bool {
 	return errors.As(err, target)
 }
 
 // NewError creates a simple error with the given text.
 // Wrapper around errors.New for convenience.
+//
+//	return log.NewError("invalid state")
 func NewError(text string) error {
 	return errors.New(text)
 }
 
 // Join combines multiple errors into one.
 // Wrapper around errors.Join for convenience.
+//
+//	return log.Join(validateErr, persistErr)
 func Join(errs ...error) error {
 	return errors.Join(errs...)
 }
@@ -130,6 +298,8 @@ func Join(errs ...error) error {
 
 // Op extracts the operation name from an error.
 // Returns empty string if the error is not an *Err.
+//
+//	op := log.Op(err) // e.g. "user.Save"
 func Op(err error) string {
 	var e *Err
 	if As(err, &e) {
@@ -140,6 +310,8 @@ func Op(err error) string {
 
 // ErrCode extracts the error code from an error.
 // Returns empty string if the error is not an *Err or has no code.
+//
+//	code := log.ErrCode(err) // e.g. "VALIDATION_FAILED"
 func ErrCode(err error) string {
 	var e *Err
 	if As(err, &e) {
@@ -150,6 +322,8 @@ func ErrCode(err error) string {
 
 // Message extracts the message from an error.
 // Returns the error's Error() string if not an *Err.
+//
+//	msg := log.Message(err)
 func Message(err error) string {
 	if err == nil {
 		return ""
@@ -163,6 +337,8 @@ func Message(err error) string {
 
 // Root returns the root cause of an error chain.
 // Unwraps until no more wrapped errors are found.
+//
+//	cause := log.Root(err)
 func Root(err error) error {
 	if err == nil {
 		return nil
@@ -178,6 +354,8 @@ func Root(err error) error {
 
 // AllOps returns an iterator over all operational contexts in the error chain.
 // It traverses the error tree using errors.Unwrap.
+//
+//	for op := range log.AllOps(err) { /* "api.Call" → "db.Query" → ... */ }
 func AllOps(err error) iter.Seq[string] {
 	return func(yield func(string) bool) {
 		for err != nil {
@@ -195,6 +373,8 @@ func AllOps(err error) iter.Seq[string] {
 
 // StackTrace returns the logical stack trace (chain of operations) from an error.
 // It returns an empty slice if no operational context is found.
+//
+//	ops := log.StackTrace(err) // ["api.Call", "db.Query", "sql.Exec"]
 func StackTrace(err error) []string {
 	var stack []string
 	for op := range AllOps(err) {
@@ -204,6 +384,8 @@ func StackTrace(err error) []string {
 }
 
 // FormatStackTrace returns a pretty-printed logical stack trace.
+//
+//	trace := log.FormatStackTrace(err) // "api.Call -> db.Query -> sql.Exec"
 func FormatStackTrace(err error) string {
 	var ops []string
 	for op := range AllOps(err) {
@@ -237,7 +419,7 @@ func LogError(err error, op, msg string) error {
 		return nil
 	}
 	wrapped := Wrap(err, op, msg)
-	defaultLogger.Error(msg, "op", op, "err", err)
+	Default().Error(msg, "op", op, "err", err)
 	return wrapped
 }
 
@@ -252,7 +434,7 @@ func LogWarn(err error, op, msg string) error {
 		return nil
 	}
 	wrapped := Wrap(err, op, msg)
-	defaultLogger.Warn(msg, "op", op, "err", err)
+	Default().Warn(msg, "op", op, "err", err)
 	return wrapped
 }
 
@@ -264,7 +446,8 @@ func LogWarn(err error, op, msg string) error {
 //	log.Must(Initialize(), "app", "startup failed")
 func Must(err error, op, msg string) {
 	if err != nil {
-		defaultLogger.Error(msg, "op", op, "err", err)
+		wrapped := Wrap(err, op, msg)
-		panic(Wrap(err, op, msg))
+		Default().Error(msg, "op", op, "err", err)
+		panic(wrapped)
 	}
 }

errors_test.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -44,6 +45,20 @@ func TestErr_Error_EmptyOp_Good(t *testing.T) {
 	assert.Equal(t, "wrapped: underlying", err.Error())
 }
 
+func TestErr_Error_EmptyMsg_Good(t *testing.T) {
+	err := &Err{Op: "api.Call", Code: "TIMEOUT"}
+	assert.Equal(t, "api.Call: [TIMEOUT]", err.Error())
+
+	err = &Err{Op: "api.Call", Err: errors.New("underlying")}
+	assert.Equal(t, "api.Call: underlying", err.Error())
+
+	err = &Err{Op: "api.Call", Code: "TIMEOUT", Err: errors.New("underlying")}
+	assert.Equal(t, "api.Call: [TIMEOUT]: underlying", err.Error())
+
+	err = &Err{Op: "api.Call"}
+	assert.Equal(t, "api.Call", err.Error())
+}
+
 func TestErr_Unwrap_Good(t *testing.T) {
 	underlying := errors.New("underlying error")
 	err := &Err{Op: "test", Msg: "wrapped", Err: underlying}
@@ -73,6 +88,20 @@ func TestE_Good_NilError(t *testing.T) {
 	assert.Equal(t, "op.Name: message", err.Error())
 }
 
+func TestEWithRecovery_Good(t *testing.T) {
+	retryAfter := time.Second * 5
+	err := EWithRecovery("op.Name", "message", nil, true, &retryAfter, "retry once")
+
+	var logErr *Err
+	assert.NotNil(t, err)
+	assert.True(t, As(err, &logErr))
+	assert.True(t, logErr.Retryable)
+	if assert.NotNil(t, logErr.RetryAfter) {
+		assert.Equal(t, retryAfter, *logErr.RetryAfter)
+	}
+	assert.Equal(t, "retry once", logErr.NextAction)
+}
+
 func TestWrap_Good(t *testing.T) {
 	underlying := errors.New("base")
 	err := Wrap(underlying, "handler.Process", "processing failed")
@@ -95,6 +124,41 @@ func TestWrap_PreservesCode_Good(t *testing.T) {
 	assert.Contains(t, outer.Error(), "[VALIDATION_ERROR]")
 }
 
+func TestWrap_PreservesCode_FromNestedErrWithEmptyOuterCode_Good(t *testing.T) {
+	inner := WrapCode(errors.New("base"), "VALIDATION_ERROR", "inner.Op", "validation failed")
+	mid := &Err{Op: "mid.Op", Msg: "mid failed", Err: inner}
+
+	outer := Wrap(mid, "outer.Op", "outer context")
+
+	assert.NotNil(t, outer)
+	assert.Equal(t, "VALIDATION_ERROR", ErrCode(outer))
+	assert.Contains(t, outer.Error(), "[VALIDATION_ERROR]")
+}
+
+func TestWrap_PreservesRecovery_Good(t *testing.T) {
+	retryAfter := 15 * time.Second
+	inner := &Err{Msg: "inner", Retryable: true, RetryAfter: &retryAfter, NextAction: "inspect input"}
+
+	outer := Wrap(inner, "outer.Op", "outer context")
+
+	assert.NotNil(t, outer)
+	var logErr *Err
+	assert.True(t, As(outer, &logErr))
+	assert.True(t, logErr.Retryable)
+	if assert.NotNil(t, logErr.RetryAfter) {
+		assert.Equal(t, retryAfter, *logErr.RetryAfter)
+	}
+	assert.Equal(t, "inspect input", logErr.NextAction)
+}
+
+func TestWrap_PreservesCode_FromNestedChain_Good(t *testing.T) {
+	root := WrapCode(errors.New("base"), "CHAIN_ERROR", "inner", "inner failed")
+	wrapped := Wrap(fmt.Errorf("mid layer: %w", root), "outer", "outer context")
+
+	assert.Equal(t, "CHAIN_ERROR", ErrCode(wrapped))
+	assert.Contains(t, wrapped.Error(), "[CHAIN_ERROR]")
+}
+
 func TestWrap_NilError_Good(t *testing.T) {
 	err := Wrap(nil, "op", "msg")
 	assert.Nil(t, err)
@@ -112,6 +176,41 @@ func TestWrapCode_Good(t *testing.T) {
 	assert.Contains(t, err.Error(), "[INVALID_INPUT]")
 }
 
+func TestWrapCode_Good_EmptyCodeDoesNotInherit(t *testing.T) {
+	inner := WrapCode(errors.New("base"), "INNER_CODE", "inner.Op", "inner failed")
+
+	outer := WrapCode(inner, "", "outer.Op", "outer failed")
+
+	var logErr *Err
+	assert.True(t, As(outer, &logErr))
+	assert.Equal(t, "", logErr.Code)
+}
+
+func TestWrapCodeWithRecovery_Good(t *testing.T) {
+	retryAfter := time.Minute
+	err := WrapCodeWithRecovery(errors.New("validation failed"), "INVALID_INPUT", "api.Validate", "bad request", true, &retryAfter, "retry with backoff")
+
+	var logErr *Err
+	assert.NotNil(t, err)
+	assert.True(t, As(err, &logErr))
+	assert.True(t, logErr.Retryable)
+	assert.NotNil(t, logErr.RetryAfter)
+	assert.Equal(t, retryAfter, *logErr.RetryAfter)
+	assert.Equal(t, "retry with backoff", logErr.NextAction)
+	assert.Equal(t, "INVALID_INPUT", logErr.Code)
+}
+
+func TestWrapCodeWithRecovery_Good_EmptyCodeDoesNotInherit(t *testing.T) {
+	retryAfter := time.Minute
+	inner := WrapCodeWithRecovery(errors.New("validation failed"), "INNER_CODE", "inner.Op", "inner failed", true, &retryAfter, "retry later")
+
+	outer := WrapCodeWithRecovery(inner, "", "outer.Op", "outer failed", true, &retryAfter, "retry later")
+
+	var logErr *Err
+	assert.True(t, As(outer, &logErr))
+	assert.Equal(t, "", logErr.Code)
+}
+
 func TestWrapCode_Good_NilError(t *testing.T) {
 	// WrapCode with nil error but with code still creates an error
 	err := WrapCode(nil, "CODE", "op", "msg")
@@ -133,6 +232,19 @@ func TestNewCode_Good(t *testing.T) {
 	assert.Nil(t, logErr.Err)
 }
 
+func TestNewCodeWithRecovery_Good(t *testing.T) {
+	retryAfter := 2 * time.Minute
+	err := NewCodeWithRecovery("NOT_FOUND", "resource not found", false, &retryAfter, "contact support")
+
+	var logErr *Err
+	assert.NotNil(t, err)
+	assert.True(t, As(err, &logErr))
+	assert.False(t, logErr.Retryable)
+	assert.NotNil(t, logErr.RetryAfter)
+	assert.Equal(t, retryAfter, *logErr.RetryAfter)
+	assert.Equal(t, "contact support", logErr.NextAction)
+}
+
 // --- Standard Library Wrapper Tests ---
 
 func TestIs_Good(t *testing.T) {
@@ -197,6 +309,42 @@ func TestErrCode_Good_Nil(t *testing.T) {
 	assert.Equal(t, "", ErrCode(nil))
 }
 
+func TestRetryAfter_Good(t *testing.T) {
+	retryAfter := 42 * time.Second
+	err := &Err{Msg: "typed", RetryAfter: &retryAfter}
+
+	got, ok := RetryAfter(err)
+	assert.True(t, ok)
+	assert.Equal(t, retryAfter, *got)
+}
+
+func TestRetryAfter_Good_NestedChain(t *testing.T) {
+	retryAfter := 42 * time.Second
+	inner := &Err{Msg: "typed", RetryAfter: &retryAfter}
+	outer := &Err{Msg: "outer", Err: inner}
+
+	got, ok := RetryAfter(outer)
+	assert.True(t, ok)
+	assert.Equal(t, retryAfter, *got)
+}
+
+func TestIsRetryable_Good(t *testing.T) {
+	err := &Err{Msg: "typed", Retryable: true}
+	assert.True(t, IsRetryable(err))
+}
+
+func TestRecoveryAction_Good(t *testing.T) {
+	err := &Err{Msg: "typed", NextAction: "inspect"}
+	assert.Equal(t, "inspect", RecoveryAction(err))
+}
+
+func TestRecoveryAction_Good_NestedChain(t *testing.T) {
+	inner := &Err{Msg: "typed", NextAction: "inspect"}
+	outer := &Err{Msg: "outer", Err: inner}
+
+	assert.Equal(t, "inspect", RecoveryAction(outer))
+}
+
 func TestMessage_Good(t *testing.T) {
 	err := E("op", "the message", errors.New("base"))
 	assert.Equal(t, "the message", Message(err))
@@ -253,6 +401,23 @@ func TestLogError_Good(t *testing.T) {
 	assert.Contains(t, output, "op=\"db.Connect\"")
 }
 
+func TestLogError_Good_LogsOriginalErrorContext(t *testing.T) {
+	var buf bytes.Buffer
+	logger := New(Options{Level: LevelDebug, Output: &buf})
+	SetDefault(logger)
+	defer SetDefault(New(Options{Level: LevelInfo}))
+
+	underlying := E("db.Query", "query failed", errors.New("timeout"))
+	err := LogError(underlying, "db.Connect", "database unavailable")
+
+	assert.NotNil(t, err)
+
+	output := buf.String()
+	assert.Contains(t, output, "op=\"db.Connect\"")
+	assert.Contains(t, output, "stack=\"db.Query\"")
+	assert.NotContains(t, output, "stack=\"db.Connect -> db.Query\"")
+}
+
 func TestLogError_Good_NilError(t *testing.T) {
 	var buf bytes.Buffer
 	logger := New(Options{Level: LevelDebug, Output: &buf})
@@ -328,18 +493,18 @@ func TestStackTrace_Good(t *testing.T) {
 	assert.Equal(t, "op3 -> op2 -> op1", formatted)
 }
 
-func TestStackTrace_PlainError(t *testing.T) {
+func TestStackTrace_Bad_PlainError(t *testing.T) {
 	err := errors.New("plain error")
 	assert.Empty(t, StackTrace(err))
 	assert.Empty(t, FormatStackTrace(err))
 }
 
-func TestStackTrace_Nil(t *testing.T) {
+func TestStackTrace_Bad_Nil(t *testing.T) {
 	assert.Empty(t, StackTrace(nil))
 	assert.Empty(t, FormatStackTrace(nil))
 }
 
-func TestStackTrace_NoOp(t *testing.T) {
+func TestStackTrace_Bad_NoOp(t *testing.T) {
 	err := &Err{Msg: "no op"}
 	assert.Empty(t, StackTrace(err))
 	assert.Empty(t, FormatStackTrace(err))

log.go

@@ -11,6 +11,7 @@ import (
 	"os"
 	"os/user"
 	"slices"
+	"strings"
 	"sync"
 	"time"
 )
@@ -32,6 +33,19 @@ const (
 	LevelDebug
 )
 
+const (
+	defaultRotationMaxSize    = 100
+	defaultRotationMaxAge     = 28
+	defaultRotationMaxBackups = 5
+)
+
+func normaliseLevel(level Level) Level {
+	if level < LevelQuiet || level > LevelDebug {
+		return LevelInfo
+	}
+	return level
+}
+
 // String returns the level name.
 func (l Level) String() string {
 	switch l {
@@ -59,13 +73,18 @@ type Logger struct {
 	// RedactKeys is a list of keys whose values should be masked in logs.
 	redactKeys []string
 
-	// Style functions for formatting (can be overridden)
+	// StyleTimestamp formats the rendered timestamp prefix.
 	StyleTimestamp func(string) string
-	StyleDebug     func(string) string
+	// StyleDebug formats the debug level prefix.
-	StyleInfo      func(string) string
+	StyleDebug func(string) string
-	StyleWarn      func(string) string
+	// StyleInfo formats the info level prefix.
-	StyleError     func(string) string
+	StyleInfo func(string) string
-	StyleSecurity  func(string) string
+	// StyleWarn formats the warning level prefix.
+	StyleWarn func(string) string
+	// StyleError formats the error level prefix.
+	StyleError func(string) string
+	// StyleSecurity formats the security event prefix.
+	StyleSecurity func(string) string
 }
 
 // RotationOptions defines the log rotation and retention policy.
@@ -93,6 +112,7 @@ type RotationOptions struct {
 
 // Options configures a Logger.
 type Options struct {
+	// Level controls which messages are emitted.
 	Level Level
 	// Output is the destination for log messages. If Rotation is provided,
 	// Output is ignored and logs are written to the rotating file instead.
@@ -108,17 +128,25 @@ type Options struct {
 var RotationWriterFactory func(RotationOptions) goio.WriteCloser
 
 // New creates a new Logger with the given options.
+//
+//	logger := log.New(log.Options{
+//	    Level:      log.LevelInfo,
+//	    Output:     os.Stdout,
+//	    RedactKeys: []string{"password", "token"},
+//	})
 func New(opts Options) *Logger {
+	level := normaliseLevel(opts.Level)
+
 	output := opts.Output
 	if opts.Rotation != nil && opts.Rotation.Filename != "" && RotationWriterFactory != nil {
-		output = RotationWriterFactory(*opts.Rotation)
+		output = RotationWriterFactory(normaliseRotationOptions(*opts.Rotation))
 	}
 	if output == nil {
 		output = os.Stderr
 	}
 
 	return &Logger{
-		level:          opts.Level,
+		level:          level,
 		output:         output,
 		redactKeys:     slices.Clone(opts.RedactKeys),
 		StyleTimestamp: identity,
@@ -130,16 +158,40 @@ func New(opts Options) *Logger {
 	}
 }
 
+func normaliseRotationOptions(opts RotationOptions) RotationOptions {
+	if opts.MaxSize <= 0 {
+		opts.MaxSize = defaultRotationMaxSize
+	}
+	if opts.MaxAge == 0 {
+		opts.MaxAge = defaultRotationMaxAge
+	}
+	if opts.MaxBackups <= 0 {
+		opts.MaxBackups = defaultRotationMaxBackups
+	}
+	return opts
+}
+
 func identity(s string) string { return s }
 
+func safeStyle(style func(string) string) func(string) string {
+	if style == nil {
+		return identity
+	}
+	return style
+}
+
 // SetLevel changes the log level.
+//
+//	logger.SetLevel(log.LevelDebug)
 func (l *Logger) SetLevel(level Level) {
 	l.mu.Lock()
-	l.level = level
+	l.level = normaliseLevel(level)
 	l.mu.Unlock()
 }
 
 // Level returns the current log level.
+//
+//	current := logger.Level()
 func (l *Logger) Level() Level {
 	l.mu.RLock()
 	defer l.mu.RUnlock()
@@ -147,13 +199,20 @@ func (l *Logger) Level() Level {
 }
 
 // SetOutput changes the output writer.
+//
+//	logger.SetOutput(os.Stdout)
 func (l *Logger) SetOutput(w goio.Writer) {
+	if w == nil {
+		w = os.Stderr
+	}
 	l.mu.Lock()
 	l.output = w
 	l.mu.Unlock()
 }
 
 // SetRedactKeys sets the keys to be redacted.
+//
+//	logger.SetRedactKeys("password", "token", "secret")
 func (l *Logger) SetRedactKeys(keys ...string) {
 	l.mu.Lock()
 	l.redactKeys = slices.Clone(keys)
@@ -167,47 +226,67 @@ func (l *Logger) shouldLog(level Level) bool {
 }
 
 func (l *Logger) log(level Level, prefix, msg string, keyvals ...any) {
+	_ = level
 	l.mu.RLock()
 	output := l.output
 	styleTimestamp := l.StyleTimestamp
 	redactKeys := l.redactKeys
 	l.mu.RUnlock()
 
+	if styleTimestamp == nil {
+		styleTimestamp = identity
+	}
 	timestamp := styleTimestamp(time.Now().Format("15:04:05"))
 
+	existing := make(map[string]struct{}, len(keyvals)/2+2)
+	for i := 0; i < len(keyvals); i += 2 {
+		if key, ok := keyvals[i].(string); ok {
+			existing[key] = struct{}{}
+		}
+	}
+
 	// Automatically extract context from error if present in keyvals
 	origLen := len(keyvals)
 	for i := 0; i < origLen; i += 2 {
-		if i+1 < origLen {
+		if i+1 >= origLen {
-			if err, ok := keyvals[i+1].(error); ok {
+			continue
-				if op := Op(err); op != "" {
+		}
-					// Check if op is already in keyvals
+		err, ok := keyvals[i+1].(error)
-					hasOp := false
+		if !ok {
-					for j := 0; j < len(keyvals); j += 2 {
+			continue
-						if k, ok := keyvals[j].(string); ok && k == "op" {
+		}
-							hasOp = true
+		var logErr *Err
-							break
+		if As(err, &logErr) {
-						}
+			if _, hasRetryable := existing["retryable"]; !hasRetryable {
-					}
+				existing["retryable"] = struct{}{}
-					if !hasOp {
+				keyvals = append(keyvals, "retryable", retryableHint(err))
-						keyvals = append(keyvals, "op", op)
+			}
-					}
+			if retryAfter, ok := RetryAfter(err); ok {
+				if _, hasRetryAfter := existing["retry_after_seconds"]; !hasRetryAfter {
+					existing["retry_after_seconds"] = struct{}{}
+					keyvals = append(keyvals, "retry_after_seconds", retryAfter.Seconds())
 				}
-				if stack := FormatStackTrace(err); stack != "" {
+			}
-					// Check if stack is already in keyvals
+			if nextAction := RecoveryAction(err); nextAction != "" {
-					hasStack := false
+				if _, hasNextAction := existing["next_action"]; !hasNextAction {
-					for j := 0; j < len(keyvals); j += 2 {
+					existing["next_action"] = struct{}{}
-						if k, ok := keyvals[j].(string); ok && k == "stack" {
+					keyvals = append(keyvals, "next_action", nextAction)
-							hasStack = true
-							break
-						}
-					}
-					if !hasStack {
-						keyvals = append(keyvals, "stack", stack)
-					}
 				}
 			}
 		}
+
+		if op := Op(err); op != "" {
+			if _, hasOp := existing["op"]; !hasOp {
+				existing["op"] = struct{}{}
+				keyvals = append(keyvals, "op", op)
+			}
+		}
+		if stack := FormatStackTrace(err); stack != "" {
+			if _, hasStack := existing["stack"]; !hasStack {
+				existing["stack"] = struct{}{}
+				keyvals = append(keyvals, "stack", stack)
+			}
+		}
 	}
 
 	// Format key-value pairs
@@ -218,69 +297,95 @@ func (l *Logger) log(level Level, prefix, msg string, keyvals ...any) {
 			if i > 0 {
 				kvStr += " "
 			}
-			key := keyvals[i]
+			key := normaliseLogText(fmt.Sprintf("%v", keyvals[i]))
 			var val any
 			if i+1 < len(keyvals) {
 				val = keyvals[i+1]
 			}
 
 			// Redaction logic
-			keyStr := fmt.Sprintf("%v", key)
+			if shouldRedact(key, redactKeys) {
-			if slices.Contains(redactKeys, keyStr) {
 				val = "[REDACTED]"
 			}
 
 			// Secure formatting to prevent log injection
 			if s, ok := val.(string); ok {
-				kvStr += fmt.Sprintf("%v=%q", key, s)
+				kvStr += fmt.Sprintf("%s=%q", key, s)
 			} else {
-				kvStr += fmt.Sprintf("%v=%v", key, val)
+				kvStr += fmt.Sprintf("%s=%v", key, normaliseLogText(fmt.Sprintf("%v", val)))
 			}
 		}
 	}
 
-	_, _ = fmt.Fprintf(output, "%s %s %s%s\n", timestamp, prefix, msg, kvStr)
+	_, _ = fmt.Fprintf(output, "%s %s %s%s\n", timestamp, prefix, normaliseLogText(msg), kvStr)
 }
 
 // Debug logs a debug message with optional key-value pairs.
+//
+//	logger.Debug("processing request", "method", "GET", "path", "/api/users")
 func (l *Logger) Debug(msg string, keyvals ...any) {
 	if l.shouldLog(LevelDebug) {
-		l.log(LevelDebug, l.StyleDebug("[DBG]"), msg, keyvals...)
+		l.mu.RLock()
+		style := safeStyle(l.StyleDebug)
+		l.mu.RUnlock()
+		l.log(LevelDebug, style("[DBG]"), msg, keyvals...)
 	}
 }
 
 // Info logs an info message with optional key-value pairs.
+//
+//	logger.Info("server started", "port", 8080)
 func (l *Logger) Info(msg string, keyvals ...any) {
 	if l.shouldLog(LevelInfo) {
-		l.log(LevelInfo, l.StyleInfo("[INF]"), msg, keyvals...)
+		l.mu.RLock()
+		style := safeStyle(l.StyleInfo)
+		l.mu.RUnlock()
+		l.log(LevelInfo, style("[INF]"), msg, keyvals...)
 	}
 }
 
 // Warn logs a warning message with optional key-value pairs.
+//
+//	logger.Warn("high memory usage", "percent", 92)
 func (l *Logger) Warn(msg string, keyvals ...any) {
 	if l.shouldLog(LevelWarn) {
-		l.log(LevelWarn, l.StyleWarn("[WRN]"), msg, keyvals...)
+		l.mu.RLock()
+		style := safeStyle(l.StyleWarn)
+		l.mu.RUnlock()
+		l.log(LevelWarn, style("[WRN]"), msg, keyvals...)
 	}
 }
 
 // Error logs an error message with optional key-value pairs.
+//
+//	logger.Error("database connection failed", "err", err, "host", "db.local")
 func (l *Logger) Error(msg string, keyvals ...any) {
 	if l.shouldLog(LevelError) {
-		l.log(LevelError, l.StyleError("[ERR]"), msg, keyvals...)
+		l.mu.RLock()
+		style := safeStyle(l.StyleError)
+		l.mu.RUnlock()
+		l.log(LevelError, style("[ERR]"), msg, keyvals...)
 	}
 }
 
 // Security logs a security event with optional key-value pairs.
 // It uses LevelError to ensure security events are visible even in restrictive
 // log configurations.
+//
+//	logger.Security("brute force detected", "ip", remoteAddr, "attempts", 50)
 func (l *Logger) Security(msg string, keyvals ...any) {
 	if l.shouldLog(LevelError) {
-		l.log(LevelError, l.StyleSecurity("[SEC]"), msg, keyvals...)
+		l.mu.RLock()
+		style := safeStyle(l.StyleSecurity)
+		l.mu.RUnlock()
+		l.log(LevelError, style("[SEC]"), msg, keyvals...)
 	}
 }
 
 // Username returns the current system username.
 // It uses os/user for reliability and falls back to environment variables.
+//
+//	user := log.Username()
 func Username() string {
 	if u, err := user.Current(); err == nil {
 		return u.Username
@@ -289,54 +394,104 @@ func Username() string {
 	if u := os.Getenv("USER"); u != "" {
 		return u
 	}
-	return os.Getenv("USERNAME")
+	if u := os.Getenv("USERNAME"); u != "" {
+		return u
+	}
+	return "unknown"
+}
+
+var logTextCleaner = strings.NewReplacer(
+	"\r", "\\r",
+	"\n", "\\n",
+	"\t", "\\t",
+)
+
+func normaliseLogText(text string) string {
+	return logTextCleaner.Replace(text)
 }
 
 // --- Default logger ---
 
 var defaultLogger = New(Options{Level: LevelInfo})
+var defaultLoggerMu sync.RWMutex
 
 // Default returns the default logger.
+//
+//	logger := log.Default()
 func Default() *Logger {
+	defaultLoggerMu.RLock()
+	defer defaultLoggerMu.RUnlock()
 	return defaultLogger
 }
 
 // SetDefault sets the default logger.
+// Passing nil is ignored to preserve the current default logger.
+//
+//	log.SetDefault(customLogger)
 func SetDefault(l *Logger) {
+	if l == nil {
+		return
+	}
+	defaultLoggerMu.Lock()
 	defaultLogger = l
+	defaultLoggerMu.Unlock()
 }
 
 // SetLevel sets the default logger's level.
+//
+//	log.SetLevel(log.LevelDebug)
 func SetLevel(level Level) {
-	defaultLogger.SetLevel(level)
+	Default().SetLevel(level)
 }
 
 // SetRedactKeys sets the default logger's redaction keys.
+//
+//	log.SetRedactKeys("password", "token")
 func SetRedactKeys(keys ...string) {
-	defaultLogger.SetRedactKeys(keys...)
+	Default().SetRedactKeys(keys...)
 }
 
 // Debug logs to the default logger.
+//
+//	log.Debug("query started", "sql", query)
 func Debug(msg string, keyvals ...any) {
-	defaultLogger.Debug(msg, keyvals...)
+	Default().Debug(msg, keyvals...)
 }
 
 // Info logs to the default logger.
+//
+//	log.Info("server ready", "port", 8080)
 func Info(msg string, keyvals ...any) {
-	defaultLogger.Info(msg, keyvals...)
+	Default().Info(msg, keyvals...)
 }
 
 // Warn logs to the default logger.
+//
+//	log.Warn("retrying request", "attempt", 2)
 func Warn(msg string, keyvals ...any) {
-	defaultLogger.Warn(msg, keyvals...)
+	Default().Warn(msg, keyvals...)
 }
 
 // Error logs to the default logger.
+//
+//	log.Error("request failed", "err", err)
 func Error(msg string, keyvals ...any) {
-	defaultLogger.Error(msg, keyvals...)
+	Default().Error(msg, keyvals...)
 }
 
 // Security logs to the default logger.
+//
+//	log.Security("suspicious login", "ip", remoteAddr)
 func Security(msg string, keyvals ...any) {
-	defaultLogger.Security(msg, keyvals...)
+	Default().Security(msg, keyvals...)
+}
+
+func shouldRedact(key any, redactKeys []string) bool {
+	keyStr := fmt.Sprintf("%v", key)
+	for _, redactKey := range redactKeys {
+		if redactKey == keyStr {
+			return true
+		}
+	}
+	return false
 }

log_test.go

@@ -2,9 +2,12 @@ package log
 
 import (
 	"bytes"
+	"errors"
 	goio "io"
+	"os"
 	"strings"
 	"testing"
+	"time"
 )
 
 // nopWriteCloser wraps a writer with a no-op Close for testing rotation.
@@ -12,7 +15,7 @@ type nopWriteCloser struct{ goio.Writer }
 
 func (nopWriteCloser) Close() error { return nil }
 
-func TestLogger_Levels(t *testing.T) {
+func TestLogger_Levels_Good(t *testing.T) {
 	tests := []struct {
 		name     string
 		level    Level
@@ -62,7 +65,7 @@ func TestLogger_Levels(t *testing.T) {
 	}
 }
 
-func TestLogger_KeyValues(t *testing.T) {
+func TestLogger_KeyValues_Good(t *testing.T) {
 	var buf bytes.Buffer
 	l := New(Options{Level: LevelDebug, Output: &buf})
 
@@ -80,7 +83,7 @@ func TestLogger_KeyValues(t *testing.T) {
 	}
 }
 
-func TestLogger_ErrorContext(t *testing.T) {
+func TestLogger_ErrorContext_Good(t *testing.T) {
 	var buf bytes.Buffer
 	l := New(Options{Output: &buf, Level: LevelInfo})
 
@@ -98,7 +101,54 @@ func TestLogger_ErrorContext(t *testing.T) {
 	}
 }
 
-func TestLogger_Redaction(t *testing.T) {
+func TestLogger_ErrorContextIncludesRecovery_Good(t *testing.T) {
+	var buf bytes.Buffer
+	l := New(Options{Output: &buf, Level: LevelInfo})
+	retryAfter := 45 * time.Second
+
+	err := EWithRecovery("retryable.Op", "temporary failure", errors.New("temporary failure"), true, &retryAfter, "retry with backoff")
+	l.Error("request failed", "err", err)
+
+	output := buf.String()
+	if !strings.Contains(output, "retryable=true") {
+		t.Errorf("expected output to contain retryable=true, got %q", output)
+	}
+	if !strings.Contains(output, "retry_after_seconds=45") {
+		t.Errorf("expected output to contain retry_after_seconds=45, got %q", output)
+	}
+	if !strings.Contains(output, "next_action=\"retry with backoff\"") {
+		t.Errorf("expected output to contain next_action=\"retry with backoff\", got %q", output)
+	}
+}
+
+func TestLogger_ErrorContextIncludesNestedRecovery_Good(t *testing.T) {
+	var buf bytes.Buffer
+	l := New(Options{Output: &buf, Level: LevelInfo})
+	retryAfter := 30 * time.Second
+
+	inner := &Err{
+		Msg:        "inner failure",
+		Retryable:  true,
+		RetryAfter: &retryAfter,
+		NextAction: "retry later",
+	}
+	outer := &Err{Msg: "outer failure", Err: inner}
+
+	l.Error("request failed", "err", outer)
+
+	output := buf.String()
+	if !strings.Contains(output, "retryable=true") {
+		t.Errorf("expected output to contain retryable=true, got %q", output)
+	}
+	if !strings.Contains(output, "retry_after_seconds=30") {
+		t.Errorf("expected output to contain retry_after_seconds=30, got %q", output)
+	}
+	if !strings.Contains(output, "next_action=\"retry later\"") {
+		t.Errorf("expected output to contain next_action=\"retry later\", got %q", output)
+	}
+}
+
+func TestLogger_Redaction_Good(t *testing.T) {
 	var buf bytes.Buffer
 	l := New(Options{
 		Level:      LevelInfo,
@@ -120,7 +170,23 @@ func TestLogger_Redaction(t *testing.T) {
 	}
 }
 
-func TestLogger_InjectionPrevention(t *testing.T) {
+func TestLogger_Redaction_Bad_CaseMismatchNotRedacted(t *testing.T) {
+	var buf bytes.Buffer
+	l := New(Options{
+		Level:      LevelInfo,
+		Output:     &buf,
+		RedactKeys: []string{"password"},
+	})
+
+	l.Info("login", "PASSWORD", "secret123")
+
+	output := buf.String()
+	if !strings.Contains(output, "PASSWORD=\"secret123\"") {
+		t.Errorf("expected case-mismatched key to remain visible, got %q", output)
+	}
+}
+
+func TestLogger_InjectionPrevention_Good(t *testing.T) {
 	var buf bytes.Buffer
 	l := New(Options{Level: LevelInfo, Output: &buf})
 
@@ -137,7 +203,44 @@ func TestLogger_InjectionPrevention(t *testing.T) {
 	}
 }
 
-func TestLogger_SetLevel(t *testing.T) {
+func TestLogger_KeySanitization_Good(t *testing.T) {
+	var buf bytes.Buffer
+	l := New(Options{Level: LevelInfo, Output: &buf})
+
+	l.Info("message", "key\nwith newline", "value\nwith newline")
+	output := buf.String()
+
+	if !strings.Contains(output, "key\\nwith newline") {
+		t.Errorf("expected sanitized key, got %q", output)
+	}
+	if !strings.Contains(output, "value\\nwith newline") {
+		t.Errorf("expected sanitized value, got %q", output)
+	}
+
+	lines := strings.Split(strings.TrimSpace(output), "\n")
+	if len(lines) != 1 {
+		t.Errorf("expected 1 line, got %d", len(lines))
+	}
+}
+
+func TestLogger_MessageSanitization_Good(t *testing.T) {
+	var buf bytes.Buffer
+	l := New(Options{Level: LevelInfo, Output: &buf})
+
+	l.Info("message\nwith\tcontrol\rchars")
+	output := buf.String()
+
+	if !strings.Contains(output, "message\\nwith\\tcontrol\\rchars") {
+		t.Errorf("expected control characters to be escaped, got %q", output)
+	}
+
+	lines := strings.Split(strings.TrimSpace(output), "\n")
+	if len(lines) != 1 {
+		t.Errorf("expected 1 line, got %d", len(lines))
+	}
+}
+
+func TestLogger_SetLevel_Good(t *testing.T) {
 	l := New(Options{Level: LevelInfo})
 
 	if l.Level() != LevelInfo {
@@ -148,9 +251,14 @@ func TestLogger_SetLevel(t *testing.T) {
 	if l.Level() != LevelDebug {
 		t.Error("expected level to be Debug after SetLevel")
 	}
+
+	l.SetLevel(99)
+	if l.Level() != LevelInfo {
+		t.Errorf("expected invalid level to default back to info, got %v", l.Level())
+	}
 }
 
-func TestLevel_String(t *testing.T) {
+func TestLevel_String_Good(t *testing.T) {
 	tests := []struct {
 		level    Level
 		expected string
@@ -172,7 +280,7 @@ func TestLevel_String(t *testing.T) {
 	}
 }
 
-func TestLogger_Security(t *testing.T) {
+func TestLogger_Security_Good(t *testing.T) {
 	var buf bytes.Buffer
 	l := New(Options{Level: LevelError, Output: &buf})
 
@@ -206,6 +314,17 @@ func TestLogger_SetOutput_Good(t *testing.T) {
 	}
 }
 
+func TestLogger_SetOutput_Bad_NilFallsBackToStderr(t *testing.T) {
+	var buf bytes.Buffer
+	l := New(Options{Level: LevelInfo, Output: &buf})
+
+	l.SetOutput(nil)
+
+	if l.output != os.Stderr {
+		t.Errorf("expected nil output to fallback to os.Stderr, got %T", l.output)
+	}
+}
+
 func TestLogger_SetRedactKeys_Good(t *testing.T) {
 	var buf bytes.Buffer
 	l := New(Options{Level: LevelInfo, Output: &buf})
@@ -291,6 +410,32 @@ func TestNew_RotationFactory_Good(t *testing.T) {
 	}
 }
 
+func TestNew_RotationFactory_Good_DefaultRetentionValues(t *testing.T) {
+	original := RotationWriterFactory
+	defer func() { RotationWriterFactory = original }()
+
+	var captured RotationOptions
+	RotationWriterFactory = func(opts RotationOptions) goio.WriteCloser {
+		captured = opts
+		return nopWriteCloser{goio.Discard}
+	}
+
+	_ = New(Options{
+		Level:    LevelInfo,
+		Rotation: &RotationOptions{Filename: "test.log"},
+	})
+
+	if captured.MaxSize != defaultRotationMaxSize {
+		t.Errorf("expected default MaxSize=%d, got %d", defaultRotationMaxSize, captured.MaxSize)
+	}
+	if captured.MaxAge != defaultRotationMaxAge {
+		t.Errorf("expected default MaxAge=%d, got %d", defaultRotationMaxAge, captured.MaxAge)
+	}
+	if captured.MaxBackups != defaultRotationMaxBackups {
+		t.Errorf("expected default MaxBackups=%d, got %d", defaultRotationMaxBackups, captured.MaxBackups)
+	}
+}
+
 func TestNew_DefaultOutput_Good(t *testing.T) {
 	// No output or rotation — should default to stderr (not nil)
 	l := New(Options{Level: LevelInfo})
@@ -299,6 +444,13 @@ func TestNew_DefaultOutput_Good(t *testing.T) {
 	}
 }
 
+func TestNew_Bad_InvalidLevelDefaultsToInfo(t *testing.T) {
+	l := New(Options{Level: Level(99)})
+	if l.Level() != LevelInfo {
+		t.Errorf("expected invalid level to default to info, got %v", l.Level())
+	}
+}
+
 func TestUsername_Good(t *testing.T) {
 	name := Username()
 	if name == "" {
@@ -337,3 +489,47 @@ func TestDefault_Good(t *testing.T) {
 		}
 	}
 }
+
+func TestDefault_Bad_SetDefaultNilIgnored(t *testing.T) {
+	original := Default()
+	var buf bytes.Buffer
+	custom := New(Options{Level: LevelInfo, Output: &buf})
+	SetDefault(custom)
+	defer SetDefault(original)
+
+	SetDefault(nil)
+
+	if Default() != custom {
+		t.Error("expected SetDefault(nil) to preserve the current default logger")
+	}
+}
+
+func TestLogger_StyleHooks_Bad_NilHooksDoNotPanic(t *testing.T) {
+	var buf bytes.Buffer
+	l := New(Options{Level: LevelDebug, Output: &buf})
+	l.StyleTimestamp = nil
+	l.StyleDebug = nil
+	l.StyleInfo = nil
+	l.StyleWarn = nil
+	l.StyleError = nil
+	l.StyleSecurity = nil
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Fatalf("expected nil style hooks not to panic, got panic: %v", r)
+		}
+	}()
+
+	l.Debug("debug")
+	l.Info("info")
+	l.Warn("warn")
+	l.Error("error")
+	l.Security("security")
+
+	output := buf.String()
+	for _, tag := range []string{"[DBG]", "[INF]", "[WRN]", "[ERR]", "[SEC]"} {
+		if !strings.Contains(output, tag) {
+			t.Errorf("expected %s in output, got %q", tag, output)
+		}
+	}
+}

specs/RFC.md

@@ -0,0 +1,266 @@
+# log
+**Import:** `dappco.re/go/core/log`
+**Files:** 2
+
+## Types
+
+### Err
+`type Err struct`
+
+Structured error wrapper that carries operation context, a human-readable message, an optional wrapped cause, and an optional machine-readable code.
+It can also carry agent-facing recovery metadata that survives wrapping and is
+surfaced automatically in structured logs.
+
+Fields:
+- `Op string`: operation name. When non-empty, `Error` prefixes the formatted message with `Op + ": "`.
+- `Msg string`: human-readable message stored on the error and returned by `Message`.
+- `Err error`: wrapped cause returned by `Unwrap`.
+- `Code string`: optional machine-readable code. When non-empty, `Error` includes it in square brackets.
+- `Retryable bool`: whether the caller can safely retry the operation.
+- `RetryAfter *time.Duration`: optional retry delay hint when `Retryable` is true.
+- `NextAction string`: suggested next step when the error is not directly retryable.
+
+Methods:
+- `func (e *Err) Error() string`: formats the error text from `Op`, `Msg`, `Code`, and `Err`. The result omits missing parts, so the output can be `"{Msg}"`, `"{Msg} [{Code}]"`, `"{Msg}: {Err}"`, `"{Op}: {Msg} [{Code}]: {Err}"`, or a cleanly collapsed form such as `"{Op}"` when no message, code, or cause is present.
+- `func (e *Err) Unwrap() error`: returns `e.Err`.
+
+### Level
+`type Level int`
+
+Logging verbosity enum used by `Logger` and `Options`.
+
+Methods:
+- `func (l Level) String() string`: returns `quiet`, `error`, `warn`, `info`, or `debug`. Any other value returns `unknown`.
+
+### Logger
+`type Logger struct`
+
+Concurrency-safe structured logger. `New` clones the configured redaction keys, stores the configured level and writer, and initializes all style hooks to identity functions.
+
+Each log call writes one line in the form `HH:MM:SS {prefix} {msg}` followed by space-separated key/value pairs. String values are rendered with Go `%q` quoting, redacted keys are replaced with `"[REDACTED]"`, a trailing key without a value renders as `<nil>`, and any `error` value in `keyvals` can cause `op`, `stack`, `retryable`, `retry_after_seconds`, and `next_action` fields to be appended automatically if those keys were not already supplied.
+
+Fields:
+- `StyleTimestamp func(string) string`: transforms the rendered `HH:MM:SS` timestamp before it is written.
+- `StyleDebug func(string) string`: transforms the debug prefix passed to debug log lines.
+- `StyleInfo func(string) string`: transforms the info prefix passed to info log lines.
+- `StyleWarn func(string) string`: transforms the warn prefix passed to warning log lines.
+- `StyleError func(string) string`: transforms the error prefix passed to error log lines.
+- `StyleSecurity func(string) string`: transforms the security prefix passed to security log lines.
+
+Methods:
+- `func (l *Logger) SetLevel(level Level)`: sets the logger’s current threshold.
+- `func (l *Logger) Level() Level`: returns the logger’s current threshold.
+- `func (l *Logger) SetOutput(w goio.Writer)`: replaces the writer used for future log lines.
+- `func (l *Logger) SetRedactKeys(keys ...string)`: replaces the exact-match key list whose values are masked during formatting.
+- `func (l *Logger) Debug(msg string, keyvals ...any)`: emits a debug line when the logger level is at least `LevelDebug`.
+- `func (l *Logger) Info(msg string, keyvals ...any)`: emits an info line when the logger level is at least `LevelInfo`.
+- `func (l *Logger) Warn(msg string, keyvals ...any)`: emits a warning line when the logger level is at least `LevelWarn`.
+- `func (l *Logger) Error(msg string, keyvals ...any)`: emits an error line when the logger level is at least `LevelError`.
+- `func (l *Logger) Security(msg string, keyvals ...any)`: emits a security line with the security style prefix and the same visibility threshold as `LevelError`.
+
+### Options
+`type Options struct`
+
+Constructor input for `New`.
+
+Fields:
+- `Level Level`: initial logger threshold.
+- `Output goio.Writer`: destination used when rotation is not selected.
+- `Rotation *RotationOptions`: optional rotation configuration. `New` uses rotation only when this field is non-nil, `Rotation.Filename` is non-empty, and `RotationWriterFactory` is non-nil.
+- `RedactKeys []string`: keys whose values should be masked in formatted log output.
+
+### RotationOptions
+`type RotationOptions struct`
+
+Rotation configuration passed through to `RotationWriterFactory` when `New` selects a rotating writer.
+
+Fields:
+- `Filename string`: log file path. `New` only attempts rotation when this field is non-empty.
+- `MaxSize int`: value forwarded to the rotation writer factory.
+- `MaxAge int`: value forwarded to the rotation writer factory.
+- `MaxBackups int`: value forwarded to the rotation writer factory.
+- `Compress bool`: value forwarded to the rotation writer factory.
+
+## Functions
+
+### AllOps
+`func AllOps(err error) iter.Seq[string]`
+
+Returns an iterator over non-empty `Op` values found by repeatedly calling `errors.Unwrap` on `err`. Operations are yielded from the outermost `*Err` to the innermost one.
+
+### As
+`func As(err error, target any) bool`
+
+Thin wrapper around `errors.As`.
+
+### Debug
+`func Debug(msg string, keyvals ...any)`
+
+Calls `Default().Debug(msg, keyvals...)`.
+
+### Default
+`func Default() *Logger`
+
+Returns the package-level default logger. The package initializes it with `New(Options{Level: LevelInfo})`.
+
+### E
+`func E(op, msg string, err error) error`
+
+Returns `&Err{Op: op, Msg: msg, Err: err}` as an `error`. It always returns a non-nil error value, even when `err` is nil.
+
+### EWithRecovery
+`func EWithRecovery(op, msg string, err error, retryable bool, retryAfter *time.Duration, nextAction string) error`
+
+Returns `&Err{Op: op, Msg: msg, Err: err}` with explicit recovery metadata
+attached to the new error value.
+
+### ErrCode
+`func ErrCode(err error) string`
+
+If `err` contains an `*Err`, returns its `Code`. Otherwise returns the empty string.
+
+### Error
+`func Error(msg string, keyvals ...any)`
+
+Calls `Default().Error(msg, keyvals...)`.
+
+### FormatStackTrace
+`func FormatStackTrace(err error) string`
+
+Collects `AllOps(err)` and joins the operations with `" -> "`. Returns the empty string when no operations are found.
+
+### Info
+`func Info(msg string, keyvals ...any)`
+
+Calls `Default().Info(msg, keyvals...)`.
+
+### Is
+`func Is(err, target error) bool`
+
+Thin wrapper around `errors.Is`.
+
+### Join
+`func Join(errs ...error) error`
+
+Thin wrapper around `errors.Join`.
+
+### IsRetryable
+`func IsRetryable(err error) bool`
+
+Returns whether the first matching `*Err` in the chain is marked retryable.
+
+### NewCodeWithRecovery
+`func NewCodeWithRecovery(code, msg string, retryable bool, retryAfter *time.Duration, nextAction string) error`
+
+Returns `&Err{Msg: msg, Code: code}` with recovery metadata attached.
+
+### LogError
+`func LogError(err error, op, msg string) error`
+
+If `err` is nil, returns nil. Otherwise wraps the error with `Wrap(err, op, msg)`, logs `msg` through the default logger at error level with key/value pairs `"op", op, "err", err`, and returns the wrapped error.
+
+### LogWarn
+`func LogWarn(err error, op, msg string) error`
+
+If `err` is nil, returns nil. Otherwise wraps the error with `Wrap(err, op, msg)`, logs `msg` through the default logger at warn level with key/value pairs `"op", op, "err", err`, and returns the wrapped error.
+
+### Message
+`func Message(err error) string`
+
+Returns the `Msg` field from the first matching `*Err`. If `err` is nil, returns the empty string. For non-`*Err` errors, returns `err.Error()`.
+
+### Must
+`func Must(err error, op, msg string)`
+
+If `err` is nil, does nothing. Otherwise logs `msg` through the default logger at error level with key/value pairs `"op", op, "err", err`, then panics with `Wrap(err, op, msg)`.
+
+### New
+`func New(opts Options) *Logger`
+
+Constructs a logger from `opts`. It prefers a rotating writer only when `opts.Rotation` is non-nil, `opts.Rotation.Filename` is non-empty, and `RotationWriterFactory` is set; otherwise it uses `opts.Output`. If neither path yields a writer, it falls back to `os.Stderr`.
+
+### NewCode
+`func NewCode(code, msg string) error`
+
+Returns `&Err{Msg: msg, Code: code}` as an `error`.
+
+### RecoveryAction
+`func RecoveryAction(err error) string`
+
+Returns the first next-action hint from the error chain.
+
+### RetryAfter
+`func RetryAfter(err error) (*time.Duration, bool)`
+
+Returns the first retry-after hint from the error chain, if present.
+
+### NewError
+`func NewError(text string) error`
+
+Thin wrapper around `errors.New`.
+
+### Op
+`func Op(err error) string`
+
+If `err` contains an `*Err`, returns its `Op`. Otherwise returns the empty string.
+
+### Root
+`func Root(err error) error`
+
+Repeatedly unwraps `err` with `errors.Unwrap` until no further wrapped error exists, then returns the last error in that chain. If `err` is nil, returns nil.
+
+### Security
+`func Security(msg string, keyvals ...any)`
+
+Calls `Default().Security(msg, keyvals...)`.
+
+### SetDefault
+`func SetDefault(l *Logger)`
+
+Replaces the package-level default logger with `l`.
+
+### SetLevel
+`func SetLevel(level Level)`
+
+Calls `Default().SetLevel(level)`.
+
+### SetRedactKeys
+`func SetRedactKeys(keys ...string)`
+
+Calls `Default().SetRedactKeys(keys...)`.
+
+### StackTrace
+`func StackTrace(err error) []string`
+
+Collects `AllOps(err)` into a slice in outermost-to-innermost order. When no operations are found, the returned slice is nil.
+
+### Username
+`func Username() string`
+
+Returns the current username by trying `user.Current()` first, then the `USER` environment variable, then the `USERNAME` environment variable.
+
+### Warn
+`func Warn(msg string, keyvals ...any)`
+
+Calls `Default().Warn(msg, keyvals...)`.
+
+### Wrap
+`func Wrap(err error, op, msg string) error`
+
+If `err` is nil, returns nil. Otherwise returns a new `*Err` containing `op`, `msg`, and `err`. If the wrapped error chain already contains an `*Err` with a non-empty `Code`, the new wrapper copies that code.
+
+### WrapCodeWithRecovery
+`func WrapCodeWithRecovery(err error, code, op, msg string, retryable bool, retryAfter *time.Duration, nextAction string) error`
+
+Returns nil only when both `err` is nil and `code` is empty. Otherwise it
+returns a wrapped `*Err` with explicit recovery metadata attached.
+
+### WrapCode
+`func WrapCode(err error, code, op, msg string) error`
+
+Returns nil only when both `err` is nil and `code` is empty. In every other case it returns `&Err{Op: op, Msg: msg, Err: err, Code: code}` as an `error`.
+
+### WrapWithRecovery
+`func WrapWithRecovery(err error, op, msg string, retryable bool, retryAfter *time.Duration, nextAction string) error`
+
+Returns nil when `err` is nil. Otherwise it returns a wrapped `*Err` with explicit recovery metadata attached.