Brummel
f26b33f345
Settled design from #153 (fieldtest friction of milestone #148): make the `aura run` cost-flag surface honest — a units/constraints note in the usage, a named non-negativity diagnostic, and a refuse-don't-guess rejection of cost flags on a non-R harness (the spec_gap; decided reject/exit-2, recorded on #153). CLI-ergonomics + one C10 ledger note only; no cost-model/R-math change. Boss-signed: grounding-check PASS (independent fresh-context agent; 6/6 load-bearing assumptions ratified by currently-green tests). refs #153