Error Codes

Normalized error codes shared across adapters and plugins.

Code	Default retryability	Typical source
`ABORTED`	`false`	Aborted send signal
`AUTH`	`false`	Invalid provider credential
`CANCELLED`	`false`	Hooks policy cancellation
`INVALID_MESSAGE`	`false`	Validation, rendering, or provider payload validation
`RECIPIENT_REJECTED`	`false`	Provider rejects the recipient
`RATE_LIMITED`	`true`	Provider rate limit
`PROVIDER_UNAVAILABLE`	`true`	Network or provider availability failure
`TIMEOUT`	`true`	Request timeout
`UNKNOWN`	`false`	An unmapped exception

PostboteError also includes message, provider, retryable, and an optional cause. The error brand is global-symbol based; use isPostboteError() for a reliable guard.