Type Alias CapsuleJointReachRule

A joint-end reach rule, injectable purely so a test can substitute a WRONG one. Under the shipped rule the clip is exactly inert — every sweep row measures identically with and without it — so deleting the clip leaves the suite green and the line reads as dead code to the next reader. The negative control (line-capsule.test.ts) feeds the pre-#1488 half-disc rule through here and asserts the sweep CHOPS, which is what makes the clip's presence observable.

Exported deliberately, despite having one in-repo caller: the docstrings above {@link} it, and a link to a non-exported symbol trips the TypeDoc warning ratchet (86/86 with the export). Do not un-export it as cleanup.