Task A of campaign phase 2: the lead-gain candidate set is now pure env, so the
live arms need no recompile.
- common_libs/guns/bitbrain_gun.nim: BB_GAINS_ENV (TR_BITBRAIN_GAINS); the
candidate list is parsed once at gun construction into a dynamic seq, so the
hit counts/hit rates are sized to it. Unset/unparsable -> the shipped
BB_CAND set [0,0.25,0.5,0.75,1.0] (byte-identical behaviour). Exactly ONE
candidate degenerates to a FIXED gain applied from the first shot (learning
bypassed), still gated to the long bands. parseGains clamps to [0,8],
de-dupes and sorts so the argmax tie rule is unchanged. The [bb] line now
prints the APPLIED gain AND the resulting angular shift, so a run's
correction is auditable from stdout.
- ModularBot_garage/src/env_report.nim: emit TR_BITBRAIN_GAINS (resolved
candidate set) and add BB_GAINS_ENV to the known-name list.
- tools/ab/arms_leadgain.txt: the 6-arm phase-2 sweep definition.
