It is almost like the GDC was thinking of that!
As for the legality of adding this to an alliance partner’s robot, I1 defines a “MAJOR MECHANISM” as “a group of COMPONENTS and/or MECHANISMS assembled together to address at least one (1) game challenge: robot movement, game piece control, field element manipulation, or performance of a scorable task.”
Although this hook is a simple mechanism, it meets the definition of a MAJOR MECHANISM and “MAJOR MECHANISMS must be built by the FIRST Robotics Competition team.” and should follow the spirit of the rule as laid out in the blue box, “Neither I1 nor the language in its Blue Box define specific thresholds for how much of a MAJOR MECHANISM must be the result of the team’s effort. I1 expects and requires the team’s honest assessment of whether they built the MAJOR MECHANISMS of their ROBOT.
Attempts to exploit loopholes in the definition of MAJOR MECHANISM in order to bypass this requirement are not in the spirit of I1 or the FIRST Robotics Competition. Examples of exploitation include:
a. assembling pieces of a MAJOR MECHANISM provided by another team
b. receiving a mostly complete MAJOR MECHANISM from another team and providing a small piece”
So the exact border line falls into a grey area, a grey area that gets very dark grey if the part suddenly appears 20 minutes after the alliance selection process.
A leading team could approach this in a couple of ways… they could have a handout describing how to build a hook, could share this handout with teams on Thursday or Friday, and let teams know that they have plenty of COTS stock for those who wish to build their own hook. They could also let teams know that having a hook like that would be something they will be looking for during the alliance selection process, should they be an alliance captain. That would give teams time to add the hook to their robot and test it during practice and/or qualifying, and the leading team would clearly be seen as “helping everyone to build their own scoring mechanisms” rather than “building parts for an alliance partner”.
This isn’t so much a “legality” issue… if a team insists that they built a part for their robot during lunch time on Saturday, I’d have a hard time proving them wrong (but it would trip my BS detectors)… but if they did it on Thursday, or over the course of the day on Friday… particularly with a bit of guidance from a senior team, well that’s what ‘helping’ is all about. This is more of a GP issue than a strict ‘rules’ issue.