The trailing-slash directory form was hardcoded to serve `browse`. Add a
`dir_tool` .zddc key (cascades leaf→root, floors at `browse`) so an
operator can point a subtree's slash form at another directory-oriented
tool — the symmetric counterpart to `default_tool` (the no-slash
"specialized app"). handler.ServeDirectory now resolves it via
zddc.DirToolAt; JSON listing requests are unaffected (raw listing
always served, so browse can still enumerate).
Also collapse the no-slash dispatch: the on-disk-directory and the
virtual-declared-path branches in main.go each carried their own copy
of "default_tool → tables-carveout-or-apps.Serve → 302", with
inconsistent ACL checks. Extract one chokepoint, serveSpecializedNoSlash,
that enforces ACL uniformly for every default_tool route.
Updates ARCHITECTURE.md and AGENTS.md: the stale "Special folders" /
hardcoded-availability sections now describe the .zddc-cascade model
(defaults.zddc.yaml, the schema-key table, the slash/no-slash
convention, WORM, standard roles).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>