Target capability constraints

Purpose and scope

Proposes rejecting compilation when a target does not meet a required gate set, connectivity or bounded reference error budget. Advisory warnings and mandatory target requirements become distinct.

Core design rules

• @target_capabilities names the profile, required gates, connectivity and error bound.
• Requirements are checked against explicit profile data; missing information is not treated as success.
• The check produces evidence and diagnostics that can be carried consistently across tools.

Example from the original

This example illustrates the design recorded in the original. It is not by itself a claim of executable or stable support; check required options and the current version.

module native_bell;
@target("superconducting");
@target_capabilities(profile: "superconducting", gate_set: ["H", "CNOT"], connectivity: "line", max_error: 0.08);

fn main() {
  let q: QReg<2> = qreg[2];
  H(q[0]);
  CNOT(q[0], q[1]);
  return q;
}

Limits and interpretation

• A reference profile error budget is not physical-device calibration or a hardware guarantee.
• A target description alone does not authorize execution with that provider.

Status and implementation boundary

The source records the runtime-experimental scope negotiated by experimental.targetCapabilityConstraints=true. Current profile and execution support require separate verification.