composition.md

Composition of full trees and addressed access

The full structural contract is WireTree = DeixisNode<Wire>, exactly parallel to Bitstore's DataTree = DeixisNode<Data>. The primitives differ only in their operation: Wire.send(message) admits interaction; Data.read() retrieves fixed bytes. Decision 0012 replaces the earlier practice of calling addressed access the full structure.

Full tree composition

Each node contains its own primitive and a complete map of byte-keyed child trees. Keys are arbitrary exact bytes; empty and non-UTF-8 keys remain distinct. A tree is finite and acyclic. The same child instance may be shared under more than one name. Construction rejects duplicate byte keys and protects the structure from mutation through caller-owned collections.

The common methods are own, children, at and decompose. Runtime construction preserves primitive/child identities and supports both directions:

decompose(compose(own, children)) ≅ { own, children }
compose(decompose(tree))         ≅ tree
select(tree, [])                 ≅ tree
select(select(tree, a), b)       ≅ select(tree, a ++ b)

The selection equation applies when the first selection exists. Missing paths return no node; they do not invoke an ancestor's own primitive as fallback. For existing paths the operation is entirely determined by structure:

send(tree, path, message) = select(tree, path).own().send(message)
read(tree, path)          = select(tree, path).own().read()

A subtree can be inserted beneath another key without changing the primitive. A retained primitive's state survives decomposition and reconstruction because reconstruction preserves that capability, rather than copying its hidden state. Complete parts also expose all the capabilities they hold. Delegate restricted access separately if the caller must not have the complete structure.

Addressed access and carriers

AddressedWire.send(path, message) preserves the former addressed interface. It can be derived from a tree with an explicit key mapping, but an arbitrary AddressedWire is not itself a tree. It may hide routes, dispatch dynamically or route through cycles; none can satisfy the complete finite structural contract by changing a type annotation.

Binding a prefix of addressed access is therefore a separate operation from structural at. A prefix can be bound without knowing whether a route exists; structural selection answers whether a node is present. Similarly, refusal to send does not prove that a child is absent.

Existing carrier paths contain Unicode-scalar strings. Tree keys contain any bytes. The unchanged bitwire/1 carrier supports the exact UTF-8 image only; an adapter must reject other keys or specify an additional encoding/profile. No implicit normalization or lossy conversion is permitted.

Endpoint extends AddressedWire with one receive attachment and closure. Selected receiving views share a dispatcher's attachment. Pure routing keeps local return identity and received context. A physical hop has additional profile-defined correlation, context and live-reference obligations. ReturnAddress.wire remains addressed because its profile has response and invocation-lifecycle paths. Replacing it with a primitive Wire would erase those operations and requires a separate explicit lifecycle design.

Ownership and evidence

Bitwire owns the declarations, laws, protocol and independent expectations. bitruntime owns production tree construction, derived operators, carriers and profile execution. Consumers own application meaning, interpretation identity and authority policy. Sharing a tree interface does not translate incompatible payloads or make an access handle proof of authorization.

The tree reference cases exercise the new structural contract using test-only interpreters. The full-tree cases run it against released bitruntime, including across its carriers, bound and served by bitruntime's Bind and Serve (the reference realization uses test-only adapters); the carrier model they describe is a test model, not part of this contract. The declared composition evidence and runnable example catalogue retain the older addressed interpretation and its versioned runtime observations. Historical green cases are not full WireTree runtime adoption. The language matrix records source declarations, publication and consumer adoption separately.