Research: concurrency and coordination pattern candidates

[Skymly]

Part of #244

Question

For the concurrency / coordination family, which new pattern domain candidates fit DesignPatterns’ primitive + compile-time-glue model?

Constraints: longlist only; new domains only; exclude work that is only an enhancement to an already-shipped domain’s API.

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

[Skymly]

Research note: docs/.Local/research/concurrency-candidates.md on branch research/concurrency-candidates (commit 186fbbe).

Candidates (longlist only)

• Channel Pipeline (staged producer–consumer) — Attribute-registered stages; generator wires typed Channel<T> edges + Keys / missing-edge diagnostics.
• Phased Barrier Coordination — Named phases + participant attributes; generator emits counts/Keys over BCL Barrier / CountdownEvent.
• Actor Mailbox — Addressable actors with typed handlers + mailbox queue; compile-time routing (not Event Aggregator pub/sub).
• Fork–Join Work Graph — Attribute DAG of work steps; generator validates acyclicity and emits join orchestration.

ROADMAP F2+/long-term enhancements of shipped domains (e.g. Composite parallel traversal, Factory pooling, async traces) are listed as EXCLUDED, not candidates. No admission gates applied; map #244 untouched.