Handoff: retrieval layer, tool-surface A/B, editing benchmark

One document covering the three connected pieces of work, what is verified,
what is not, and where every artifact lives. Written for a reader who was not
here.

Marked explicitly as unverified: the sidecar key fix (bakes were unreachable
from the tool layer because the key included the caller's id; fixed, but the
confirming run did not complete), and the sidecar read path end to end
through library_read / library_links.

Marked explicitly as wrong and unfixed: the citator join, where evidence_ids
carry paragraph pinpoints so keys like rvtak2005bcca293para4 match nothing.
The C4 conclusion that citator witnesses are "unjoinable on this bed" is a
defect in our key normalisation, not a fact about the data.

Also records the claim that reversed: the address grammar alone costs 14.6%
MORE than the surface it replaces, and progressive disclosure is what pays
for it. An earlier "23% cheaper" came from a partial run with three changes
bundled.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01H9ToHYJVDxfeJcJwdzrP2H