Surgical add of the two radar-authored planning docs onto architecture (both new
files, no conflict). Migration strategy: duplicate->cutover->diverge, strangler edge
+ layer-split shadow-diff, host-trio critical path. abstractions.md is the evidence
base the strategy cites (A1 done, W1/W4/W8 substrate-adoption findings).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
