The real jcalixte/notes clone (570 MB pack, 1179 files) proved both index
strategies are O(N_tree) and unshippable: index.write re-hashes the tree
(611 s), and the index-free read_tree is 77 s cold and OOMs the mmap cache
(zlib crash). Record the run in the tradeoff curve, revise the verdict to an
O(depth) TreeBuilder walk, and add a handoff note with the design, firmware
call sites, and bench steps for the next session.
