[codex] Preserve specialized TypeVar bounds

[cneuralnetwork]

Fixes #3285.

Summary

This fixes a false-positive bad-argument-type error when looking up a classmethod through a type[T] where T is a protocol-bounded TypeVar whose bound is itself specialized, for example T: SQLExpr[Any].

The PR changes recursive type-argument truncation so it only erases generic arguments when there is an actual recursive path back to the same class. Non-recursive specialized bounds such as P[Any] are now preserved.

Root Cause

TParams::truncate_recursive_targs was intentionally preventing fixpoint growth for recursive TypeVar bounds. The old predicate was too broad: it stripped type arguments from any ClassType whose formal type parameters had non-trivial restrictions.

That meant a bound like:

P_co = TypeVar("P_co", bound="P[Any]", covariant=True)

could be truncated from P[Any] to bare P because P's own type parameter had a bound. Later, attribute lookup on type[P_co] instantiated classmethod parameters from bare P, so the method leaked P's class TypeVar instead of using the specialized Any from the bound.

In the original issue this made:

self._expr.from_elementwise

look like:

(cls: type[SQLExprT], func: (Sequence[NativeExprT]) -> NativeExprT) -> None

instead of the expected:

(cls: type[SQLExprT], func: (Sequence[Any]) -> Any) -> None

Fix

The truncation logic now walks the restriction graph and only strips ClassType arguments when the class's embedded type parameters can reach back to the same class through their own bounds or constraints.

That keeps the recursion guard for shapes like Bar[Any] where Bar participates in its own bound cycle, while preserving ordinary specialized bounds used for protocol classmethod lookup.

Tests

Added a regression test covering a reduced protocol form of the issue:

class Namespace(Protocol[P_co, T_co]):
    @property
    def item(self) -> type[P_co]: ...

    def test(self) -> None:
        def f(x: Sequence[T_co]) -> T_co:
            return x[0]

        self.item.make(f)

Validation run locally:

cargo test test_protocol_typevar_bound_preserves_specialized_targs
cargo run -q -p pyrefly --bin pyrefly -- check /tmp/pyrefly_issue_3285.py
cargo test test_recursively_constrained_typevar
python3 test.py --no-test --no-conformance --no-jsonschema
git diff --check

I also reran a reveal_type probe for the original reproducer and confirmed the classmethod parameter is now specialized as (Sequence[Any]) -> Any.

AI Disclosure

This PR was prepared with help from Codex.