Design typed instruction programs for logical QEC and physical lowering

[qciaran]

Summary

• propose a Rust-owned InstrProgram with reusable InstrModule definitions and appendable typed InstrGraph bodies
• generalize PECOS original QuantumCircuit late-bound instruction idea into stable typed definitions, calls, selectable implementations, hierarchy, and deterministic resolution
• keep the generic layer deliberately smaller than a general compiler IR and generate PHIR as the MLIR-like compiler artifact
• define QEC as typed semantic interfaces covering code blocks, logical transformations, logical/physical Pauli frames, conditional control, and protocol plans
• describe thin Python wrappers with ergonomic APIs matching Rust
• retain the Guppy to HUGR/QIS to QIS trace to normalized TickCircuit to DEM route while adding Rust-only PHIR emission
• connect the proposal to issues [RFC] Layered abstractions and an HDL-style design model for QEC #508 through Document layered QEC abstractions and end-to-end workflows #516

Scope

This is a design-only draft. It adds no Rust or Python implementation code.

Testing

Documentation-only change. Markdown fence, whitespace, and Git diff checks pass.