CPU limit

Convert a relative quota into cpu.max and define behaviour when exhausted. Preserve earlier capabilities and use the fixture only to make observation deterministic.

Contract

The harness receives a JSON process description and returns a syscall, mount, and limit plan. Real privileged execution stays outside the runner, but the plan must match Linux.

{
  "op": "cpu-limit",
  "name": "demo",
  "pid": 42,
  "quota": 0.5,
  "periodUs": 100000
}

produces exactly:

{
  "writes": [
    ["demo/cpu.max", "50000 100000"],
    ["demo/cgroup.procs", "42"]
  ]
}

Emit compact JSON with a final newline. Invalid input leaves stdout empty, writes error to stderr, and exits non-zero.

Design and limits

Separate policy, mutable state, and system effects. Make resource ownership, cleanup order, and pre/post-operation invariants explicit. Do not replace the central mechanism with a simulation: the fixture controls inputs and time while your code implements isolation, memory, or synchronisation as appropriate.

Test empty boundaries, mid-operation failures, and idempotent cleanup. Sort output only at the presentation boundary.

Acceptance

• The example produces the exact output.
• Resources are not leaked and work is not duplicated.
• Failure leaves the system coherent.