Research: messaging and command-routing pattern candidates

[Skymly]

Part of #244

Question

For the messaging / command routing family, which new pattern domain candidates fit DesignPatterns’ primitive + compile-time-glue model (including but not limited to Command routing vs MediatR-shaped approaches)?

Constraints: longlist only; new domains only; note factual overlap with shipped Event Aggregator where relevant — do not decide admission.

Output: 2–4 candidates (name + one-line shape). Research note on research/ branch; link from this issue.

[Skymly]

Research complete

Longlist for messaging / command-routing new domains (no admission):

1. Command Router (request/response) — 1:1 typed Send/TrySend with [RegisterCommandHandler] → generated registry + missing/duplicate-handler diagnostics (MediatR IRequest shape; not EA 1:N Publish).
2. Request Pipeline Behaviors — ordered cross-cutting wrappers around a single command handler, composed at compile time (MediatR IPipelineBehavior; EA has fan-out, not request pipeline).
3. Stream Request Router — 1:1 progressive IAsyncEnumerable<T> responses with compile-time handler binding (MediatR IStreamRequest; no EA analogue).
4. Correlated Request/Reply Messenger — in-process request/reply with correlation id + typed reply routing (addresses EA documented non-goal of request/response correlation IDs).

Overlap note: MediatR INotification / 1:N pub-sub overlaps shipped Event Aggregator — notification-shaped ideas omitted from the longlist.

Note: docs/.Local/research/messaging-command-candidates.md on branch research/messaging-command-candidates.

Map #244 not edited.