2.x — research (history slot)

Per-era research (spike/exploration) record for the 2.x architecture track. This is part of the versioned history beneath the living architecture (see ../../README.md for the boundary and decay rules).

This slot exists so the decay path has a home: when a living exploration is superseded, it is demoted into the matching research/ directory of its era — history accrues by version, nothing is deleted.

Empty until a living research artifact decays into the 2.x era.