Accepted answer
Seven sessions a week against 900 kcal a day — 6300 kcal for the week — and at that intake the binding constraint is almost never the session count. Protein at 4 kcal per gram is the reason: 100 g a day is 400 kcal, 44 per cent of 900, and 2800 kcal of the 6300 for the week spoken for before anything else is eaten. 7 sessions also has to be recovered from on 900 kcal, and recovery is the first thing an energy deficit takes. Load matters more than frequency here: the stimulus that preserves mass is mechanical tension, so keep the weight and cut the volume rather than the reverse. None of this is medical or dietary advice.
The short version: two to four sessions weekly, roughly ten sets per muscle group per week, loads maintained, effort close to but short of failure.
Two sessions per muscle group per week outperforms one at matched volume in most of the published comparisons, mainly through better session quality.
Session performance is the practical readiness signal. Two consecutive sessions where loads drop at matched effort usually means recovery, sleep or intake rather than programming.
Load-matched comparisons show that maintaining intensity preserves strength and lean mass in a deficit better than reducing load and increasing repetitions.
One to three reps in reserve. Failure costs more than it returns here.