A capability reading must be tied to the runner that made it, so the grants
part can tell an older runner's reading from the running one's.
Builds: design 46 7 §6 (the announcement carries the runner's fingerprint), lead answer A-203 (key `fingerprint`)
Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h