feat!: receive parallels send — Client::onMessage delivers the default transport only

[genmon]

Summary

• Breaking: Client::onMessage now fires only for messages arriving on the default transport — the receive-side mirror of Client::send(doc) routing to the default transport only. The guard is evaluated per dispatch, so a runtime setDefaultTransport() switch takes effect immediately. defaultTransport = null now closes the default lane in both directions.
• Every other transport delivers via its per-transport hooks (onText/onBinary/MQTT's topic-aware onMessage), which become the receive path for non-default transports.
• New: UdpTransport::onText(cb) — raw per-packet receive hook, same idiom as WebSocketTransport::onText (UDP previously had no per-transport receive path).
• Version → 0.6.0-dev; changelog + CLAUDE.md updated.

Why

One rule in both directions: the default transport is the client-level lane; everything else is per-transport. This removes the aggregate-dispatch ambiguity that made multi-transport consumers filter by transport name, and it lets topic-aware consumers (e.g. MQTT topic routing in downstream layers) own their delivery without double-dispatch through the client callback. Groundwork for channel-based routing in Resident/Hawthorn (which needs MQTT consumed via its topic hook only).

Migration

Multi-transport users who relied on onMessage receiving all transports' messages should register per-transport hooks for the non-default transports (or setDefaultTransport to the lane they want at the client level). Downstream: Resident ≥0.7 defaults defaultTransport to "ws" when unset and a host is configured.

Tests

• 4 new contract tests in test_client (default-only dispatch, per-transport hook delivery on non-default transports, runtime default switch, null-default closed lane); 4 pre-existing tests adapted to the new contract (no assertions weakened).
• ./tools/run-tests.py unit: 163/163 pass; static-analysis clean.

🤖 Generated with Claude Code