Raised as the hardest test of the rule: a board showing nodes, modules,
pipelines, agents and tasks wants to read a dozen stores, and under exclusive
ownership it can read none of them.
It survives, and not by luck. The board is a SURFACE, and surfaces already may
not do this — the skeleton puts `api/` in the control plane as the one interface
every surface speaks to, and tier 3 as thin, no logic. A board reading stores
directly is a surface reaching past the context that owns the data, which the
tier rule forbids for reasons that have nothing to do with databases.
So it is not a counter-example; it is an instance the rule catches. And the two
rules turn out to be one rule seen from two sides: exclusive ownership is the
tier rule expressed in terms of storage.
The general shape for anything needing to see across many things: consume the
record and own your own view. A reporting context builds a projection from
events and reads its own store, never anybody else's.
The cost said plainly rather than buried: a projection is more work than a join,
and it lags. A board queries the mesh's own database directly today — ordinary,
working — and this rule makes that a migration rather than a preference. The
reason to pay it is §4's already-measured cost, not elegance.
jschoubben
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