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Tekashi 6ix9ine already knows what he'll be up to after he serves his 3-month prison sentence next year ... because a judge also ordered him to 12 months of supervised release with some pretty strict conditions.

According to court papers, obtained by TMZ, the rapper's supervised release will include a mental health treatment program focused on anger management and an outpatient drug treatment program. Getty

Last week, 6ix9ine told us he wasn't worried about doing his prison bid -- set to start January 6 -- because he plans on using the time to get in shape.

The "Gooba" artist said he's all but guaranteed to be kept out of the general population behind bars because of his "snitch" status, and he told us he plans to put the seclusion to good use.

Currently walking aro

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