# Diagnostics (Phase 0)
Phase 0 diagnostics are CLI stderr lines of the form:
```text
error[<category>]: <message>; remediation: <hint>
```
Categories: `config`, `profile`, `unsupported`, `validation`, `internal`, `io`.
Structured JSON Lines tracing, handle IDs, packet/PC context, and sanitizer findings arrive with later phases. Logging must remain bounded and must not leak secrets by default once traces exist.