Lifts the error-signal slice of F.0 forward as a D.0 prelude. ANSI
strip + canonical bash/sh error fingerprints classify each command's
post-execution output window; Command gains errored / output_bytes
fields. PII discipline preserved — only a bool and an int leave the
helper, the stripped output text is dropped on return.
Drives D.1 (cognitive_load error_rate term) and D.5–D.7 (error_resilience
family). Phase F.0 will subsume this with PS1 + exit-code parsing.
