Spell it out...
Is it not true that the GC and landlord are free-riding on your design effort?
When a project is design-build...
You as EC need some boiler-plate protecting you from free-riding.
I'd start with copy-writing my submissions and establish ownership of the plans....
If, subsequently, the GC just happens to have followed the submitted design...
It's time for court.
I'd also tack on a liquidated damages clause to any design-build.
If the player wants to use submitted proposals then a fee for services rendered is due.
Free-riding is going to be the bane of D/B until some construct brings it to a halt.
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Everyone: post your solutions.