Enforced by the database
Every record belongs to one company. The database itself refuses to show one company’s rows to another, so a mistake in the application alone cannot leak data across. Uploaded files are stored in a separate space per company.
Why departments share
Marketing needs to know what the website promised; finance needs to know what marketing offered. Inside one company, departments read each other’s documents and a shared company memory, and each entry says where it came from. That is what stops a team from contradicting itself.
