A concrete class that leaves an abstract CLR base member unimplemented is SPY0908 CS0534 — the checker never refuses it

[antonsynd]

Found during the #2138 fix (plan-0ca7b7 verification, 2026-09-27). Same result at BASE acd1d40, b59615b and after the #2138 fix.

import system.collections.generic as scg

class Rev(scg.Comparer[int]):
    @override
    def compare(self, x: int) -> int:   # arity mismatch: not an override of Compare(int, int)
        return x

def main():
    print(Rev().compare(1))

This is SPY0908 CS0534 ("'Rev' does not implement inherited abstract member 'Comparer.Compare(int, int)'"). An abstract Sharpy base gets a semantic refusal for an unimplemented abstract member. A CLR base should get the same, naming the member in python spelling (compare(x: int, y: int) -> int), and the @override arity mismatch should report once. Class contract (#2138 ruling): the override and abstractness rules read a CLR base's members the same way they read a Sharpy base's. The base-member lookup is now FindClrOverrideTarget. Meta-class: SPY0908 as a net.

[antonsynd]

Batching 2026-09-30 @ db8e05b — charter .claude/plans/remediation-round-2026-09-20-batching.md §3.26, P31 — CLR-base subclassing totality (order N20).

Contract (the #2138 ruling): the override, abstractness, base-constructor and interface-implementation rules read a CLR base exactly as they read a Sharpy base — an unimplemented abstract CLR member, a CLR base without a parameterless constructor, a module-qualified annotation, or a nullable-spelled interface parameter is decided in Semantic with python-spelled member names, never CS0534/CS7036/CS0535 behind SPY0908. Standing harness: ClrBaseOverrideRouteMatrixTests (extend the base-kind and member-state axes). Lane / reach: ice · program; FIRST in the group. This issue is the class tracker. No seam hypothesis — the plan measures the seam.

#2117 cell 2 posted here: class F(IFormattable) with def to_string(self, format: str?, provider: IFormatProvider?) -> str → SPY0908 CS0535 (the nullable parameter spelling does not match the interface member) @ acd1d40 (HEAD = BASE). Lane ice, reach program. Found by the plan-0ca7b7 class-cure review.