fix: type the middleware factory to FastStream's construction contract - #39
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ty 0.0.69 added `unbound-type-variable` and the weekly dependency check went red: `_DIMiddlewareFactory.__call__` declared `*args: P.args, **kwargs: P.kwargs` with the ParamSpec `P` bound to nothing. It was never solvable, which is why the code carried two `# ty: ignore[invalid-argument-type]` comments conceding it did not match `BrokerMiddleware`. Declare FastStream's real contract instead -- `__call__(msg, /, *, context: ContextRepo) -> _DiMiddleware`, mirrored on `_DiMiddleware.__init__` -- and drop `P` plus `typing.Generic[P]`. Both ignore comments come out and `add_middleware(...)` now type-checks on its own, so a future upstream contract change is a ty error at the call site rather than a first-message runtime failure. `msg: object` rather than `Any`: the protocol's message parameter is contravariant and the value is only forwarded to `BaseMiddleware.__init__`. This fired the revisit trigger on the two-class-split decision. Collapsing to `functools.partial` was built and measured -- it is ~10 LOC shorter and equally clean -- but rejected: `partial` types as `(*args: Any, **kwargs: Any)` and satisfies any protocol, so breaking the construction contract under it leaves ty silent. The decision file records the outcome and a new trigger. Closes #38 Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Closes #38.
ty0.0.69 addedunbound-type-variableand the weekly dependency check went red:_DIMiddlewareFactory.__call__declared*args: P.args, **kwargs: P.kwargswithPbound to nothing — never solvable, which is why the code carried two# ty: ignore[invalid-argument-type]comments conceding it did not matchBrokerMiddleware. This declares FastStream's real contract instead, and both ignores come out.Rationale, alternatives, and verification:
planning/changes/2026-08-10.01-middleware-contract-typed.md.Collapsing to
functools.partial(the revisit trigger on the two-class-split decision) was built and measured, then rejected —partialtypes as(*args: Any, **kwargs: Any)and satisfies any protocol, so a contract break under it leavestysilent. That file records the outcome and a new trigger.Verified locally on the upgraded lock:
just lint-ciclean, 6 passed, 100% coverage.