what defines "possession?"
When a VRC-specific definition of a word is not presented in the Game Manual, a dictionary definition should be used. The Oxford dictionary definition of "possession" is "the state of having, owning, or controlling something".
It is important to remember that the only mention of the word "possession" in the VRC Tower Takeover is in rule G12d:
G12> Don’t destroy other Robots. But, be prepared to encounter defense. Strategies aimed solely at the destruction, damage, tipping over, or Entanglement of opposing Robots are not part of the ethos of the VEX Robotics Competition and are not allowed. If the tipping, Entanglement, or damage is ruled to be intentional or egregious, the offending Team may be Disqualified from that Match. Repeated
offenses could result in Disqualification from the entirety of the competition.
d. Game elements in possession of a Robot are an extension of that Robot. Therefore, Entanglement (e.g., grasping, hooking, attaching) with Cubes that are in the possession of an opposing Robot is a violation of this rule.
As noted in the Q&A that you linked, the primary intent of this rule is to provide a specific interpretation of SG7 as it should be applied to G12:
<SG7> Use Cubes to play the game. Cubes may not be used to accomplish actions that would be otherwise illegal if they were attempted by Robot mechanisms. Examples include (but are not limited to):
• Encroaching upon an opponent’s Protected Zone per <SG3>.
• Interfering with an opponent’s Autonomous Period per <SG2>.
When a Head Referee is making a G12 judgment call, their primary concern should be determining whether the destruction, damage, tipping over, or Entanglement was intentional, incidental, egregious, etc. The nuances of the definition of the word "possession" should ultimately be irrelevant in this evaluation. If a scenario does present itself where the Head Referee's decision hinges solely upon determining whether the Robot in question was "having, owning, or controlling" the Cube, then we would direct them to rule G3, "Use common sense".