fix: tuple_the_args binds to its own signature; all_pk_signature keeps a forced keyword-only; replace_kwargs_using drops a source *args

[thorwhalen]

Resolves the two design questions left open by #92, decided with a use-site inventory across i2's 102 local dependents and an independent adversarial review. The decisions, options and evidence are on the issues: #78 and #93.

Changes (all in i2/signatures.py)

• ch_variadics_to_non_variadic_kind / tuple_the_args (tuple_the_args: passing the tupled *args by keyword fails, and ch_func_to_all_pk can't handle a required keyword-only after *args #93 part 1): the wrapper binds the call to the signature it advertises (Sig.map_arguments) and rebuilds the call to the original function with _args_and_kwargs_from_all_pk_arguments (the helper Cloud sweep: fix ch_func_to_all_pk with *args, partialx reordering, pyproject + uv CI, runnable README #92 added, now shared). The tupled param can be given by keyword, defaults skipped before it are filled, and a variadic keyword given by name as a dict is spread. Calls the advertised signature rejects raise FuncCallNotMatchingSignature (a TypeError). On 0.1.74 even tuple_the_args(lambda a, b=1, *args: ...)(1) raised IndexError.
• all_pk_signature (tuple_the_args: passing the tupled *args by keyword fails, and ch_func_to_all_pk can't handle a required keyword-only after *args #93 part 2): a required keyword-only param after a param with a default stays keyword-only, and so does everything after it (and after an untupled *args), instead of the constructor raising. ch_func_to_all_pk(lambda x, *y, z: ...) is now (x, y=(), *, z).
• replace_kwargs_using (Change replace_kwargs_using so it will create keyword-only params for wrapped variadic #78): a source *args is no longer injected as a required keyword-only param the target could never forward.

Behaviour changes, deliberate, for direct tuple_the_args users only: an unknown keyword for a function without **kwargs now raises instead of being silently dropped; a by-name kwargs={...} dict is spread instead of silently dropped.

Tests

• i2: 805 passed, 2 xfailed (Cloud sweep: fix ch_func_to_all_pk with *args, partialx reordering, pyproject + uv CI, runnable README #92 baseline: 785 / 2). 26 new tests + 5 doctests, written before the implementation.
• Dependents, run against this branch with the local editable i2 (all direct users of the changed functions plus Cloud sweep: fix ch_func_to_all_pk with *args, partialx reordering, pyproject + uv CI, runnable README #92's gate set): meshed 60 passed, config2py 96, dol 591, ju 11, lined 6, oa 7. py2http: 3 passed + 1 collection error identical on master (test-side arity bug, unrelated). aix: conftest import error from a broken pyOpenSSL install, unrelated.
• Probe: a meshed DAG with nodes shaped f(x, *y, z) and g(a, *args, **kw) builds and runs; both crashed at construction before.
• Adversarial review (separate agent, ≈430 calls compared with 0.1.74): APPROVE with findings; one folded in (the untupled *args rule), one filed as ch_func_to_all_pk: unify the excess-keyword policy of the with-*args and without-*args paths #95.

Closes #78
Closes #93

https://claude.ai/code/session_01MCpYkDGuVEygBHheTCcURV