release: 0.2.5840 — live walker and outline/read on miss

Stamp the next patch after v0.2.5839. Agents get a just-added file from
codedb_outline or codedb_read without calling codedb_index first, and
the live walker skips unchanged directories while still seeing in-place
edits.

Co-Authored-By: Codegraff <blackfloofie@codegraff.com>