V47 Gate 3: Define seller and buyer state-machine law #1109

Job	Run time
Validate GitHub Actions workflows	25s
Lint, Type-Check & Build	2m 49s
CodeQL Analysis	-1s
Unit & Integration Tests (mocks)	55s
Super Linter (misc files)	0s
E2E, Visual & DB Tests	-1s
	4m 7s

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