docs: MESHBAY_DESIGN.md — one reference for the design

Thirty documents under docs/ described this system between them: two
architecture drafts, three security reviews, eleven design notes, a roadmap and
a decisions file. Reading any one of them meant following cross-references into
four others, and several were flatly wrong — the keystore KDF, the protocol
version, and four features whose headers still said "not implemented" months
after they shipped.

This is the synthesis. It states design rather than history: a section says why
the node wraps the group key itself, not which finding made it necessary.
Development history, spikes and reversed directions are gone. The security
findings survive as section 13, where each label names the invariant it stands
for today rather than the defect it was reported as.

Two things it is careful about, because hundreds of code comments depend on
them. Every short label — C1, H3, NS6, T3, C5b, W2, E9, F1 — is defined in
section 13, including the three colliding namespaces (each review numbered its
findings from C1, and the code means the second review's). And section 16 maps
every "<doc> section n" reference the code makes onto its replacement, so no
comment has to be edited to stay resolvable.

transfers-v1.md comes in from outside the tree with it. The lease design is
section 5.5; what a synthesis cannot carry is that document's failure-mode
analysis — every way a slot can be lost, every way a client can be left
waiting — and what a live pass found after the work was called done.

Every claim was checked against the code rather than the drafts.
Suites green: 2256 passed, 4 skipped.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YVoHVCcfBqud6ZjG4db3y7

0 files changed, 0 insertions, 0 deletions