The question again: can you stipulate some thing which is neither temporally delimited nor composed of parts? I suggest not.

either there is a foundation, or there's a vicious infinite regress of ever-deeper layers of reality - which I reject. — Relativist

So you acknowledge that science can’t say what the foundation is, but you nevertheless claim, presumably as an act of faith, that if there is a foundation, then it must be material in nature.

At some stage in history materialism might have been able to claim that the atom was imperishable and eternal - which was, after all, the basis of materialism in Greek philosophy - but that is no longer considered feasible. Fundamental particles, so-called, have an intrinsically ambiguous nature, and they seem to be at bottom to be best conceived as an excitation of fields, however fields might be conceived.

I personally reject deism because it depends on an infinitely complex intelligence, with magical knowledge, just happening to exist by brute fact. — Relativist

That’s a Richard Dawkins argument - that whatever constructs must be more complex than what is constructed by it. But in the classical tradition, God is not complex at all, but is simple. And the best analogy I can think of for that is - you! Your body comprises billions upon billions of cells, the brain is the most complex natural phenomenon known to science with more neural connections than stars in the sky (or so I once read). And yet, you yourself are a simple unity. That, I think is the meaning (or one meaning) of ‘imago dei’.

The question again: can you stipulate some thing which is neither temporally delimited nor composed of parts? I suggest not. — Wayfarer

Even a God is temporally delimited if the past is finite. He simply exists at all times. The same is true of a material foundation. Regarding parts:why assume something exists without parts? I gave a good reason to believe the past is finite and there's a bottom layer of reality. I've never encountered a reason to assume the foundation of existence lacks parts. If there is, then it would be easy to stipulate that, and then build an ontology based on it.

So you acknowledge that science can’t say what the foundation is, but you nevertheless claim, presumably as an act of faith, that if there is a foundation, then it must be material in nature. — Wayfarer

Not an act of faith: an inference to best explanation. I see no reason to think anything immaterial exists. An immaterial foundation adds no explanatory power, so it's unparsimonious. A 3-omni God is unparsimonious to the extreme.

At some stage in history materialism might have been able to claim that the atom was imperishable and eternal - which was, after all, the basis of materialism in Greek philosophy - but that is no longer considered feasible. Fundamental particles, so-called, have an intrinsically ambiguous nature, and they seem to be at bottom to be best conceived as an excitation of fields, however fields might be conceived. — Wayfarer

Sure. Quantum field theory proposes that quantum fields (perhaps a single quantum field- in a sense, one "part") may constitute the bottom layer of reality.

Regardless, there are good reasons to believe the world is fundamentally quantum mechanical, and an implication is that our intuitions (which are the primary tool of metaphysics) are problematic for developing a reliable metaphysical theory.

That’s a Richard Dawkins argument - that whatever constructs must be more complex than what is constructed by it. But in the classical tradition, God is not complex at all, but is simple. — Wayfarer

I didn't assert there to be some metaphysical rule that, "whatever constructs must be more complex than what is constructed by it". Rather, I pointed to the complexity of God's knowledge. Divine simplicity seems a rationalization, one that depends on treating knowledge as a magical property. Every verifiable fact points to knowledge being composed of data, and data being encoded. The assumption of a 3-omni God is treated as a carte blanche magical answer to any question, and theists never address the prima facie implausibility of omniscience.

the brain is the most complex natural phenomenon known to science with more neural connections than stars in the sky (or so I once read). And yet, you yourself are a simple unity. — Wayfarer

When we look at a picture of a triangle, how many things do we see? We see 4 things: the sides, and the triangle. The triangle is a "unity" (a single thing) but is more than just 3 lines (contrast it with 3 unconnected lines on a page). So a triangle is more complex than the individual lines that composed it, just like I am more complex than the particles that comprise me. So I accept calling me a "unity", but not simple.