A merge produces a tiered plan the mesh keeps (hq ADR 0162)

A module's dependencies are one relation in the catalogue — stands-on, packages, built-by, declared —
answered by one call. A merge takes what moved and everything reachable from it, sorts the set into
tiers (a code dependency in the same tier, a build dependency after its base is built, a runtime
dependency after the build machine is built and running; the build machine's own base comes first,
built by the one that runs), writes the plan to the store, asks the first tier and returns. Every
outcome advances the plan; a ticker advances what outcomes cannot; a controller replaced mid-plan
resumes it. status lists open plans and names one that has waited too long.

cmd/mesh-controller/build.go

@@ -581,6 +581,8 @@ type answers struct {
 	// pair that answers "has it caught up", which waiting alone cannot (the sent digest is
 	// recorded at send, not at apply).
 	reported []inventory.Reported
+	// plans is what the last merges produced and where each stands (novox/hq ADR 0162).
+	plans []inventory.Plan
 	// refused is why a machine cannot be worked out at all, by name. A different thing from every
 	// other answer here: those are about a machine that was told something, and this is about one
 	// that cannot be told anything — it never reaches waiting, because nothing was computed for it