Module boundary_config 

TC.3 — the config schema / value boundary: arena on the wire, tree in the host.

Design: docs/dev/architecture/typed-configuration.md.

WIT has no recursive types. A schema and a value are both trees, and the obvious spelling — a variant whose arm holds another variant — does not parse: “type config-schema depends on itself”. So both cross as an arena: a flat list of nodes plus the index of the root, children referenced by index. This module is where that arena becomes a tree and back.

What the boundary has to defend against

An arena is guest-controlled input in a shape that invites two failures no other boundary in this crate has:

• an index that points nowhere — trivially rejected, and
• an index that points back up the tree, i.e. a cycle. Following one naively is unbounded recursion on the host’s stack, from a value a plugin chose. The tree-building walk therefore carries the set of nodes currently on its own path and refuses a node it is already inside.

Both are typed errors, never a trap and never a panic: a malformed declaration registers nothing and the plugin is told so, the same contract register-option has for a default that does not parse.

Enums

ArenaError

What went wrong turning an arena into a tree. Rendered into the false / warn paths the config seam already uses — a guest never traps over one.

Functions

schema_from_wit

A guest’s schema arena as a ConfigSchema.

schema_to_wit

A ConfigSchema as an arena for the guest. The mirror of schema_from_wit, for :describe-option-shaped reads from a plugin.

value_from_wit

A guest’s value arena as a ConfigValue.

value_to_wit

A ConfigValue as an arena for the guest.