Replace `getattr` introspection with `system.option()` for mixing kernels

[jc-macdonald]

Problem Resolved

The op_engine provider currently reads mixing kernels from the system via getattr(system, "mixing_kernels", {}).

Update (Apr 8): The engine provider code already uses system.option("mixing_kernels", None) — the getattr pattern described originally was already replaced. The system-side fix (op_system populating self.options) landed in op_system PR #56 (merged Apr 8).

Remaining work

The only remaining introspection in the engine provider is:

stepper: SystemProtocol = system._stepper  # noqa: SLF001

This should be replaced with system.bind() now that flepimop2 PR #182 has merged (Apr 8). This is tracked in #49.

Scope

• Can be closed together with Replace system._stepper access with public bind API #49 (one-line change)
• Blocked by op_system update flepimop2 provider pacakge #12 Unblocked — op_system PR Update pyproject.toml metadata, closes #38 #56 wired mixing_kernels into self.options
• Blocked by flepimop2 #131 No longer relevant — ModuleABC.options + option() is the standard mechanism

Related

• op_system PR Update pyproject.toml metadata, closes #38 #56 (merged) — wired mixing_kernels into self.options
• Replace system._stepper access with public bind API #49 — replace system._stepper with system.bind()
• Implement validate_system() in flepimop2 provider #41 — extend validate_system() to also use system.option()