A `**kwargs` collector beside named parameters needs the remainder

Type: bug (NilPy call lowering) — Track N by ownership, but see the pin note: it cannot be shipped from a worker session.
Split from [[bug-n-star-forwarder-spreads-a-dict-onto-a-kwargs-callee]], fixed 2026-08-17 for the kwIdx = 0 case only.

Repro

def f(a=1, **kw):
    return a * 100 + len(kw)

print(f(**{"a": 5, "x": 7, "y": 8}))


CPython	`502` — `a=5`, `kw={"x":7,"y":8}`
pxx	`TypeError: forwarded call got 3 arguments, expected 2 to 2`

Why it was left failing rather than half-fixed

The collector case was fixed for a callee whose ONLY parameter is the collector, where the whole dict goes in and nothing is consumed first. Extending the same code to kwIdx > 0 is a two-line change and would be wrong: it would hand kw the entire dict, answering len(kw) = 3 where CPython says 1. A wrong value is worse than the error, so kwIdx > 0 is explicitly reset to -1 in PyStarForwardCall and keeps the old behaviour.

What it needs, and why a worker cannot ship it

A runtime helper that returns the dict minus a set of consumed names — pystar_kwrest(d, n1, n2, ...) or equivalent. pylib.pas today has pystar_arg_kw, pystar_has, pystar_argc, pystar_check_arity / _kw, pystar_no_kwargs, and nothing that subtracts.

pylib.pas is compiler/builtin/**, so the change needs make stabilize-fast && make pin — Track B and the lib tests build with $(PXX_STABLE) and cannot see an unpinned builtin. A pin holds the repo lock and stalls every lane, which makes it coordinator-scheduled. Do not claim this as a worker. (devdocs/dev/session-roster.md.)

Sketch, once someone with the pin takes it

pystar_kwrest(d: TPyDict; const names: array of AnsiString): TPyDict — a copy of d without the listed keys. The frontend knows the named parameters, so the name list is a compile-time constant, exactly as pystar_arg_kw already receives a name literal per slot.
In PyStarForwardCall, stop resetting kwIdx > 0 to -1; set total := kwIdx (the named parameters are the ones before the collector) and assign pystar_kwrest(dict, <the kwIdx names>) to the collector's slot instead of the dict itself.
The arity guard stays the list-only pystar_check_arity — keys landing on named slots must not count as positional arguments. Note the guard's dict splice is conditional on the same flag; both must move together, which is the step that was got wrong once already.
CPython also raises TypeError: got multiple values for argument 'a' when a key duplicates an explicitly-passed positional. Not modelled; decide whether to implement or leave it.

Gate