Inter-processor Communication (IPC) Subsystem

Design notes for the typed IPC stack. The current trait stack, transports, and doorbells are documented in the IPC introduction and in each crate’s README; these chapters record the reasoning and proposals behind them.

• IPC QoS Design — a proposal for priority and back-pressure across channels. Not implemented.
• IPC Design — the original vision for the doorbell → transport → codec → channel layering. Crate names and trait signatures have since changed; the layering has not.

The register model of each doorbell — IPCC, MU, and HSEM — is documented on its consortium_core::bell module, next to the shared wait protocol.