Empty tuple construction raises KeyError #2168

Bug Description

Constructing an empty tuple inside a Warp kernel raises KeyError: 'args'. A zero-element tuple should be a valid statically shaped value with length zero.

import warp as wp


@wp.kernel(enable_backward=False)
def evaluate(out: wp.array[int]):
    values = ()
    out[0] = len(values)


out = wp.zeros(1, dtype=int, device="cpu")
wp.launch(evaluate, dim=1, inputs=[out], device="cpu")
print(out.numpy())

Expected: [0].

Actual: KeyError: 'args', from tuple_value_func() in warp/_src/builtins.py:

return tuple_t(arg_types["args"], arg_values["args"])

The variadic argument mappings omit args for a zero-argument call. Tuple construction should handle that case and support the resulting value consistently in length queries and function calls.

Related: #2099, #2100, #2101, #2166, #2167. This reproducer disables backward generation and does not use nesting, reassignment, or unpacking.

System Information

• Warp 1.20.0.dev0, main commit 0c1ed78f7.
• Python 3.12.3, Linux x86_64, CPU device.
• Reproduced before applying tuple fixes; failure occurs during code generation.