feat(kernel-utils): narrow default-guarded exos

[ci-belphegor]

Explanation

Most exos in this repo are built with makeDefaultExo, which produces M.interface(name, {}, { defaultGuards: 'passable' }) — an empty methodGuards map, so there is no per-method guard to conjoin a delta onto. Without this PR, narrow cannot narrow almost any existing exo: 79 non-test files use makeDefaultExo against 9 with explicit method guards.

defaultGuards: 'passable' means every method admits any passable arguments, so for a method absent from methodGuards a delta of length n synthesizes:

M.callWhen(...deltaPatterns).rest(M.any()).returns(M.any());

Sound on the same grounds as the general case: the synthesized guard admits no more calls than the base's own, and the method still forwards unaltered.

This replaces only the defaultGuards: 'passable' arm of the error PR 5 left as a seam. Unmarks one ratchet case.

Notes for reviewers

defaultGuards: 'raw' keeps throwing, deliberately. Raw guards pass arguments unmarshalled, which is not "admits any passable argument," so the soundness argument does not transfer. The it.each case that previously covered the 'passable' error now covers 'raw', so the surviving arm keeps its coverage rather than quietly becoming untested.

A length-0 delta is a proven no-op, not an approximation: the test pins the whole shape — zero required positions, zero optionals, and a rest guard admitting 'anything' and 42. So it is ⊆ with equality, which is the claim the design needs.

The cost, documented at the synthesis site. Such a base names no methods, so a delta naming one the base does not implement is indistinguishable from one it does, and no error can be raised at narrowing time. A misspelled method therefore mints a forwarder for a method that does not exist — which rejects at call time with target has no method "..." rather than silently returning undefined. That is why PR 6 refused an optional call in the forwarding path.

Probing past the case's own assertion shows the synthesized guard genuinely enforces, including .. rejection through the rest position: rejected:… ...rest: [0]: ".." - Must fail negated pattern: "..". A makeDefaultExo base with no guards of its own ends up as tightly scoped as an explicitly-guarded one.

Stack

PR 8 of 12. Base: #1053.