65f7e608410bed97e852c6eea3afc4273dd4269d  Fix outside-flat-tree TODO

Classified as not security-relevant.
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: security_assert (+4.87), area:third_party/blink/renderer/core/ (+2.5), surgical (+1.3)