Make EventSubscriptionAgentFamily.DatabaseKeyOf public

[jeremydmiller]

EventSubscriptionAgentFamily.DatabaseKeyOf (src/Wolverine/Runtime/Agents/EventSubscriptionAgentFamily.cs:327) is internal, so anything outside Wolverine that wants to group event-subscription agents by the database they belong to has to re-implement the agent URI grammar.

internal static string DatabaseKeyOf(Uri uri)
    => uri.Segments.Length >= 3
        ? $"{uri.Host}/{uri.Segments[1].Trim('/')}/{uri.Segments[2].Trim('/')}"
        : uri.AbsoluteUri;

That grammar is exactly what group affinity keys on when distributing agents, so a consumer reasoning about agent placement per database — a test asserting co-location, an admin view, a readiness probe — needs the same key, and today can only get it by copying it.

This is already happening inside this repo

src/Persistence/MartenTests/MultiTenancy/blue_green_version_bump_assignment.cs:221-226 copies the implementation verbatim:

// The (type, name, databaseId) prefix of an agent URI, mirroring the internal
// EventSubscriptionAgentFamily.DatabaseKeyOf that group affinity keys on.
private static string DatabaseKeyOf(Uri uri) =>
    uri.Segments.Length >= 3
        ? $"{uri.Host}/{uri.Segments[1].Trim('/')}/{uri.Segments[2].Trim('/')}"
        : uri.AbsoluteUri;

while its sibling tests (sharded_two_databases_affine_colocation.cs:150, durability_projection_affinity_real_stores.cs:124) call the internal directly. So the duplication the request is about already exists in Wolverine's own test suite, and a copy can silently drift from the real distribution key it's supposed to mirror.

Ask

Make DatabaseKeyOf public. TenantNeutralKeyOf (:351) is worth considering in the same pass — it's the supersession relation's key and already has full XML docs written as if it were public, and CoreTests reaches for it too (src/Testing/CoreTests/Runtime/Agents/event_subscription_family_cardinality_assignment.cs:373).

Consistent with the existing position that consumers should not hand-build event-subscription agent URIs but call the public helpers — this is the read side of the same rule.

Raised from marten#5170, whose reporter runs a 512-shard-database deployment and hit this writing a test that reasons about agent placement per database.