ores.cpp.history-provider-registrar

A junction is stored with its history: each link has a version, an author, a reason and a validity range, and a closing ends the range and deletes nothing. Until a junction asked for it, nothing read that history back. A junction model states :history: true in its * Flags to get the surface below. It is opt-in, because a provider nothing wires into its component's registrar is dead code.

• A link has two keys, so a provider cannot be read by one link's id. A junction's provider is read by the id of its parent side (the side that states :list_by:, the left when both or neither does) and answers every version of every link of that parent, closed links included. The facet adds the repository read read_all_by_<parent>, which returns a <junction>_history_row.
• The history row holds the domain type beside closed_at, and the actor and the time flat, which is what the history builder reads. The domain type is final, so the row composes it. A link is closed by ending its validity, not by writing a version, so a version that ended because the link was closed carries closed_at, and a version that a later version replaced does not. The store records when a link ended and not who ended it, so a closing has no author.
• The field mapper names the link by both keys in its first field, ID, so the versions of one link pair up in a stream that holds many. The provider numbers and diffs each link on its own, because a version number is a link's.
• The provider needs the junction's own read code (<component>::<name>:read), or the code the model names with :history_read_permission:. A history holds every version of the rows its reads serve, so it must not be easier to read than they are.
• A junction column is rendered by type. A type the table in core.py (_HISTORY_VALUE_EXPRESSIONS) does not name is refused when the model is generated, so a history never leaves a field out without saying so.

The per-component registrar.cpp still lists each provider by hand. Add the include and the call when a junction states :history: true.

Replaces the pattern of hand-wiring one ~10-line register_history_provider() lambda per entity directly into each component's registrar.cpp. That hand-maintained surface has already drifted: refdata's registrar registers only 53 of its 64 mapper-bearing entities. A small per-component aggregator (not generated; it mirrors ores::refdata::core::messaging::registrar) calls each generated per-entity function, the same way it already calls the CRUD register_<entity>_handlers() functions. refdata's registrar keeps its current 53 calls, so the registered key set is unchanged. The 11 mapper-bearing entities with no provider today stay unregistered, with identical runtime behaviour, until their own wiring work adds them.