Module reload 

Per-kind hot-reload discipline orchestration.

ReloadDispatcher is invoked between the drain and commit phases of Uni::reload. By the time it runs, the old plugin has already been removed from the registry (so new captures cannot see its surfaces), but in-flight queries that captured Arc<dyn Foo> before the swap still operate against the old instances.

The dispatcher’s job is to run the per-kind handoff each surface needs before committing the new plugin’s registrations. The handoffs are spelled out below:

Surface	Discipline
Scalar / aggregate / …	Clean — no protocol step needed.
StorageBackend	Clean — old Storage continues until drained.
IndexKindProvider	persist() on old handle → open() on new.
BackgroundJobProvider	Clean — next tick picks up the new provider.
CdcOutputProvider	checkpoint() on old → start(lsn) on new.
CrdtKindProvider	Schema-compat round-trip — hard error on mismatch.
LogicalTypeProvider	Arrow extension contract unchanged — hard error.

Per-kind handoffs that the trait surface already exposes (e.g., CdcStream::checkpoint) are invoked directly. Surfaces that need a richer contract (CRDT / logical-type schema-compat) get a default-method on the trait (schema_compat_check, compat_check) that providers can override.

Stateful surfaces with in-flight private resources (live IndexHandles, open CdcStreams) are reload-managed by the host that owns those resources — the dispatcher receives them through the ReloadKindHandlers builder rather than by registry walk, because the registry only tracks providers, not the per-instance resources those providers spawn.

Structs

CdcHandoff

One live CDC stream and the new provider that will resume it.

IndexHandoff

One live index handle and the new provider that will reopen it.

OldProviders

Pre-swap snapshot of the old plugin’s stateful providers.

ReloadDispatcher

Orchestrates per-kind reload discipline between drain and commit.

ReloadKindHandlers

Host-supplied handlers wiring per-kind in-flight resources into the reload pipeline.

ReloadOutcome

The outcome of a successful reload — opaque container for any new in-flight resources the dispatcher constructed (reopened index handles, restarted CDC streams) so the host can re-attach them.