As we know, it is impossible to record a pre-recorded midi clip session into an arrangement on a single midi track simultaneously with a live performance, because Ableton has set the priority so that starting the clip blocks the input of signals from the keyboard (but not vice versa)!
Therefore, we have to use two tracks: a service track (with a pre-recorded playback) and a main track that will record the combined signals from the keyboard and from the service track.
I need to block the signals of a pre-recorded midi clip located on a service track when I press any note key on the main track, in order to replace some of the playback notes with a live performance when recording a set.
However, this simple task cannot be solved by simply assigning note keys to control the trigger, as Ableton uses them in "toggle" mode instead of "momentary" mode for some reason, and simply releasing the keys to resume playback is not enough (they need to be pressed again).
To overcome this limitation, I can convert the note information to Control Change momentary and use it to control the trigger.
The problem is that Ableton doesn't have a service device that can send MIDI control signals (CC#) without delay to the "Remote Control" panel for midi-mapping (in Windows, this can only be done through a third-party virtual driver like LoopMIDI or LoopBe). Unfortunately, all of these third-party devices have a few-millisecond delay, which causes the trigger to fire with a certain delay relative to the MIDI note of the pressed key! As a result of this, some midi notes of the session clip (which were launched in the interval between pressing the note key and triggering the service track disabling trigger) cause false instrument triggers.
Of course, it is possible to artificially delay all note signals from the keyboard by the amount of virtual midi driver delay, but this option is not suitable for live performance, as the total delay will become noticeable when combined with audio interface delays, causing a "sluggish" performance.
It seems to me that if the regular "External Instrument" service device had the ability to send midi signals directly to the midi track inputs, then it would be possible to transmit CC# without delay (as well as musical information), but this is not possible at the moment.
Is there a way to solve this technical issue in a different way?