Review found the first pass aliased its answer under both ends of a mapping, which is
wrong wherever two mappings share a number: the alias lands on a key belonging to another
mapping, the later write wins, and the filter and the container then disagree — the very
fault this change exists to close. Two reproduced cases: a module publishing 8080:80 beside
9090:8080 had an explicit setting silently overwritten; a module publishing 4001:80 beside
4002:80 composed both containers onto one machine port, where before it was safely refused.
Now a mapping's answer is filed once, under the end the module names in its listens — the
number the plan, the filter, the openings, the guard and the consumer all ask for — and a
key that names two mappings is refused in the same words as a setting that does.
Also: the guard assertion in the end-to-end test failed open when the resource was absent;
the plan-mirroring helper now says it stands in only where the plan does not allocate, and
the assertions it feeds are narrowed to the port under test.
A module publishing `2222:22` — the machine's own ssh daemon holds 22, so
the module takes 2222 and says so in `listens` — could not be moved. The
setting was read against the last segment of each mapping alone, so the
number the module uses everywhere else was refused as a port it does not
publish, and the node's every push failed for as long as the setting was
stored. The one key that was accepted, the container's own port, was then
read only when the container's mapping was rewritten: the mapping moved
and the ports map, the filter, the adopted node's openings, its guard and
what a consumer is told all stayed on the number the software had left.
Either end of a mapping now names it, and a given port comes back under
both, so every reader finds the same number under the key it holds.
Ambiguity is refused where it is real — one number naming two different
mappings, or the two ends of one mapping given two different numbers.
jschoubben