CLAUDE: item-4 R3c - timestamp matching keys on canonical sec_usec prefix (merged labels carry -N suffix)

First A/B run 07/20 00:22 failed loud: merged-stack slice labels are
'<ts>-0' while -CUAS-RT-LOG labels are bare '<ts>' - exact match missed
all 497. tsKey() takes the leading digits/underscore run from both sides.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>