As one way of leaving the victim of a public execution sufficiently intact for a magician to use it as a meat puppet, let me present:
In this method, the condemned is brought to the place of execution, where a large, tall, thick-walled glass vessel stands, filled with water perhaps half-way up. There is a platform around the top of the vessel, and the condemned is brought up to it, possibly stripped off so that it can be shown that the condemned has no breathing tube hidden in their clothing (and to titillate the crowd), their feet shackled to a metal gridwork platform, which is then slowly lowered into the glass vessel, where the watching crowd can observe the condemned's slow descent into the water and their death struggles as they descend below the surface, and even approach the vessel and jeer at the condemned through the glass.
For criminals convicted of the more heinous crimes for which the sentence is execution, the experience of drowning can be repeated many times, submerging the condemned until they fall unconscious, then swiftly extracting them, reviving them and repeating the process.
For more entertainment, the heavy metal grid to which the condemned is shackled can be lowered on ropes, and the condemned's hands left unbound (but unable to undo the shackles, which would be locked or bolted closed) so that they can hold onto the rim of the vessel and keep themselves above the water until they tire and lose grip and fall into the water, or for more certainty, the grid can be lowered on poles, so that it can be pushed down.
The glass vessel need not be as clear as modern glass to be sufficiently clear to serve the purpose of allowing others to see a person inside it, and glass is a material known since ancient times.
For more entertainment, this means of execution is not 100% certain. The condemned may smuggle in a key for the shackle locks (Chinese locks were pretty simple) or may secrete a length of tubing in certain body cavities, thus prolonging their struggles, or both. Where the authorities really want someone to die, such devices could be "overlooked" , but there could be guards above who could remove any breathing apparatus after some time (or pour water into it), and if the condemned gets free of the shackles, guards could close a spiked grate over the vessel and if necessary, stand on it. Otherwise, stripping the condemned and conducting a last-moment body-cavity search could both eliminate such possibilities and further titillate the crowd
Another option, if rainfall is heavy and common, is to place the condemned in an empty vessel for a certain amount of time, but the vessel will be filled by rainfall collected from nearby roofs, leaving a degree of uncertainty as to whether the condemned will live or die, depending upon the "will of the gods" (more accurately, the vagaries of the weather).
The beauty of drowning for this purpose is that it does relatively little damage to the body, and unless fatal, can be treated fairly rapidly, leaving the victim capable of action shortly thereafter. Lung infections may be an issue, but if the magic that makes a body into a meat puppet is as destructive as the OP says, then that won't be an issue.
One possible drawback of this method is that drowning tends to lead to raised blood pressure that may result in burst blood vessels on/in/around the eyes (potential partial or complete blindness) in particular, but also visible on the skin on other parts of the body and/or cerebral haemorrhage (strokes) that may leave a victim in a less-than-completely-useable state, but this will not occur in many cases.