e3e3003de50fb5686ce6ae0fc145b6fc94f84a95  [line-clamp] line-clamp: auto cannot clamp between sibling blocks

Classified as not security-relevant.
Triage note: Reworks LineClampUpdater::autoClampPoint/isAutoLineClampRoot and adds clampAfterBox plumbing for the auto line-clamp point. Pure layout-feature logic for css-overflow-4 line clamping; no security bug addressed.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+6.47), null_guard (+2.59), clamp_saturate (+1.8), msg_soft (+1.0), msg_noise (-2.5), area:Source/WebCore/layout (+2.0)