GENERAL NOTES

The definition that survives every stratum: a router is an address space, a matching function, and transition semantics. BGP matches prefixes and forwards with no memory; an HTTP framework matches path patterns into a stateless response; an edge ruleset rewrites and proxies; a SPA router matches a URL into a view tree through a cancellable lifecycle; a state router matches into a named hierarchy through guarded, resolving transitions.

What changes with ascent is the transition. At the bedrock a transition is a forwarding decision that forgets itself immediately. Each stratum upward, transitions acquire more: statefulness, interceptability, cancellation, resolved data, meaning. By the surface a transition is a first-class object with a lifecycle — which is precisely the layer sheet 1 drew.

Why this sheet is mostly writing: no mechanism spans these strata — an IP hop and a ui-view activation share a definition, not a wire. Drawing more than a core sample here would be decoration, and the reference's own rule applies: the drawing earns exactly as much ink as the mechanism deserves.