A method fetched with getattr() crashed when called without its defaults

Reported 2026-10-20 by neo-73. getattr(c, "f")(1.0) against def f(self, x, limit=50) compiled cleanly and died with SIGSEGV (rc 139) on x86-64 and aarch64. c.f(1.0) and m = c.f; m(1.0) were fine, as was a getattr call that wrote every argument.

Cause: the runtime getattr path (pydynattr_get's method-as-value arm) built the bound pair with pybound_new_star, which carries no PYSIG record. The call bridge fills omitted parameters only from that record, so it entered the two-parameter body through a one-argument call. m = c.f gets its record at compile time.

Fix: take the method's PYSIG record from its RTTI (the extra word after the kinds and names, RTTI_METH_FLAG_HASSIG), the same record pyeval's reflected call reads, and build the pair with pybound_new_sig. Keyword arguments through a getattr'd method now bind by name as well.

Test: test_nilpy_getattr_method_value_fills_its_defaults (python3's output; also matches on aarch64 under qemu).