[VDR][v0.6.0] Surprising / destructive CLI defaults

[anwithk]

Theme issue grouping v0.6.0-cycle VDR findings: Surprising / destructive CLI defaults.

Finding	Severity	Summary
CLI-00845c9f	🟠 high	gym env test with no arguments silently starts a ~2-hour, ~145 GB all-servers run

Child issues are linked as sub-issues below.

_{DX review Gym-1-20260821203248 — incremental from v0.5.0 to fa0d25158. Parent tracker #2214.}