The layout paragraph the unit asks for: server.rs as the server, the
router and the request machinery; one tools/<group>.rs per tool group
with its router; tools/helpers.rs for the helpers several groups share;
server_tests.rs for the tests that span the surface and each group's own
tests in its file. plan/served.md's U0a "As built" block records the
split, the two departures (settings_tools as the module name, the test
bodies beside server.rs) and the stale 118-tool count (the surface is
122, identical to main's).
swaits
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