/*
Package xerrors provides structured application errors with stable machine-readable
codes, human-readable messages, cause chaining, and key-value context fields.

Each error carries a [Code] that maps to a well-known category (invalid input,
not found, internal, etc.) and is stable across versions — safe to persist,
transmit in API responses, or switch on programmatically.

# Basic usage

	err := xerrors.New(xerrors.ErrNotFound, "user not found")

	// With cause chaining
	err := xerrors.Wrap(xerrors.ErrInternal, "failed to query database", dbErr)

	// Convenience constructors
	err := xerrors.NotFound("user %s not found", userID)

	// Builder pattern
	err := xerrors.New(xerrors.ErrInvalidInput, "validation failed").
	    WithContext("field", "email").
	    WithContext("tag", "required")

# Cause chaining

[Err.Unwrap] is implemented, so [errors.Is] and [errors.As] walk the full
cause chain:

	if errors.Is(err, io.ErrUnexpectedEOF) { ... }

	var e *xerrors.Err
	if errors.As(err, &e) {
	    log.Println(e.Code())
	}

# Structured logging (duck-typing bridge)

[Err.ErrorCode] and [Err.ErrorContext] satisfy the private interfaces that logz
defines internally. Passing an *Err to logger.Error automatically enriches the
log record with error_code and context fields — without xerrors importing logz
or logz importing xerrors.
*/
package xerrors