Send files over 64 KiB by digest through the bus's object bucket to nodes that read them, grant it, and warn at 75 percent (issues 1696, 1697, 1698; ADR 0486 step 3)

A node that reports file-references gets the digest and size of each file over 64 KiB that may travel so, and the content is put in
the bucket declaration-files before the declaration is sent; others get every content inline. The controller alone writes the
bucket and node-engines read an object by name (the four grants the node-engine's own fetch makes, no list, no write). An object
goes a day after no node's latest declaration names it. The near-limit condition warns at 75 percent, and a test holds the control
node's declaration, in the reference form, under half the bus's largest message.

cmd/mesh-controller/declaration_room.go

@@ -13,8 +13,8 @@ import (
 
 // **A declaration is one bus message, and the bus's largest message is a cliff** (novox/hq issue 1689). On 2026-10-21
 // the control node's declaration passed it by 2 KB and nothing reached that node until two assignments were undone.
-// So the size is measured at every send: a warning condition from 90% of the limit, urgent over it, cleared when
-// the declaration is back under 90%. The limit is the connection's own, not a constant.
+// So the size is measured at every send: a warning condition from 75% of the limit (ADR 0486 §8, issue 1698: it was 90% while every file travelled inline), urgent over it, cleared when
+// the declaration is back under 75%. The limit is the connection's own, not a constant.
 
 // kindDeclarationNearLimit is a declaration at or near the bus's largest message.
 const kindDeclarationNearLimit = "declaration-near-limit"