[jeremydmiller]

Fixes #3438.

The gap

The main-store integration aliases EventSubscriptionAgentFamily to both IAgentFamily and IEventSubscriptionAgentFamily. The ancillary integration registered only the concrete type, with a standing // TODO -- watch the service registrations. So a host whose only store wanting managed distribution is ancillary — no main AddMarten that opts in — registered no IEventSubscriptionAgentFamily. Wolverine's managed distribution and external tooling (CritterWatch's projection admin: rebuild/pause/restart) resolve the family through that interface and got an empty result.

What I found beyond the issue

The issue's repro assumes an AncillaryMartenIntegration.UseWolverineManagedEventSubscriptionDistribution flag — which didn't exist. And the per-store IProjectionCoordinator<T> resolver only consulted the main MartenIntegration, which is null/absent for an ancillary-only host. So the fix is three coordinated parts, not a one-line alias add:

1. New flag UseWolverineManagedEventSubscriptionDistribution on AncillaryMartenIntegration, mirroring the main store's. This is the opt-in an ancillary-only host previously had no way to express.
2. Gated alias registration. When the flag is set, the ancillary path registers the two interface aliases via TryAddSingleton — Try so a main store that already aliased them wins and one family instance (it already takes IEnumerable<IEventStore>) covers every store. Gated on the flag because NodeAgentController distributes the agents of every registered IAgentFamily; an ancillary host that never opted in must not suddenly start distributing.
3. Resolver consults the ancillary flag too, so an ancillary-only host gets the managed WolverineProjectionCoordinator<T> instead of silently falling back to the non-managed coordinator.

Test

ancillary_managed_distribution_family_registration: an ancillary store opts in while the main store deliberately does not, so any family resolving through the interface must come from the ancillary path. Asserts the family resolves through IEventSubscriptionAgentFamily, is present as an IAgentFamily for distribution, and that the ancillary store gets the managed coordinator.

Verified red/green: with the flag present but the registration reverted, all three assertions fail; with the fix they pass. The existing with_ancillary_stores tests (main+ancillary) still pass — no regression on that path. Full wolverine.slnx builds clean (0 warnings).

Note: one unrelated multi-node failover test (tenant_partitioned_distribution_multinode.agents_fail_over...) flaked under full-suite load and passes in isolation; it uses a main store, not ancillary, so it's untouched by this change.

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