ADR 0143: a consumer verifies the grant it is given

A grant is four facts and a credential — the provision, the machine, the port, and
who the consumer is when it connects — and it is the whole mechanism by which
anything in the mesh reaches anything else. The mesh asserted it and never found
out whether it was true. Issue 145 is what that cost: eleven hours of 'every module
current with its source' while a module could not reach its database.

The consumer verifies it, from its own network position. Not the control plane,
which reaches the address by a path no consumer uses. Not the machine, whose own
packets carried a source address the filter admitted while every container's was
refused — so a host-side check would have passed throughout the outage it exists to
catch. That is inference from the rule that was loaded, stated as such.

A connection and nothing more; speaking each provision's protocol would be a second
implementation of every provision. One failure is not news, only consecutive ones,
and the count is reported rather than the last attempt. A consumer that is not
running reads unchecked, which is a different sentence from broken.

What it costs to be wrong is the constraint on all of it: a check that calls a
working provision broken trains a reader to ignore the report.

02-DECISIONS/README.md

@@ -223,6 +223,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0139** — [A network is forwarded because a module declared it](0139-a-network-is-forwarded-because-a-module-declared-it.md)  *(superseded)*
 - **0140** — [The filter constrains what arrives from outside, and says nothing about a machine's own guests](0140-the-filter-constrains-what-arrives-from-outside.md)
 - **0141** — [The host delivers its own successor, and versions live side by side](0141-the-host-delivers-its-own-successor.md)
+- **0143** — [A consumer verifies the grant it is given](0143-a-consumer-verifies-the-grant-it-is-given.md)
 
 ### How it is built