Law enforcement sources tell TMZ, cops were called to the Malibu home of 38-year-old Courtney Wagner last Sunday -- when someone heard a woman screaming ... followed by a gunshot.

When officers arrived, we're told Courtney was found in possession of cocaine and heroin. She was arrested on suspicion of felony drug possession.

The other person involved in the argument -- a male -- was placed under arrest for negligent discharge of a firearm. We're told nobody was injured.

Courtney has since posted $10,000 bail. It's unclear if the other person is still in custody. - more on this story

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