A sink is a role, not a type: recording is an out-of-graph side effect a
node performs in eval, pushing to a destination it holds as a field. No
Sink type, no trait, no engine sink-awareness. The engine stays the
router for in-graph routing (edge table = graph-as-data); the node-side
push is the only out-of-graph escape, and that boundary is the
determinism boundary. A node may be producer and sink at once (C8 both).
Engine surface shrinks: Ctx gains now(); the observe index (field,
bounds check, per-cycle collection) is removed; bootstrap drops its 4th
param; run returns (). Recording streams are sparse and timestamped
(only fired cycles), replacing the dense Vec<Option<row>>.
Realization notes land on C8 and C22; no new contract.
refs #2
Brummel
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