apologies if this is old news, haven't walked the entire 57 page thread to check, but just encountered this in my game.
Disassembly of less than one complete part ends with negative component counts, and unlimited disassembly potential.
fresh start, conventional, no pre-assigned tech
SM mode, gifted myself all the engine techs, to produce a single size 50 photonic engine, gifted the design tech.
Then SM Added the component to the stockpile. Then removed all tech, returning me to Conventional start.
Confirmed with checking the design tech, can't build anything but starter tech.
Then designed a new ship, really just a small cargo hold in a hull. It fits 0.4 of a 50HS engine. That leaves 0.6 in the planet stockpile.
Stockpile now shows 0x engines. Disassembly gets me to -1x, etc.
A couple hundred repeated disassemblies gets me the complete engine tech line. I can now build photonic drives, while still being conventional... can't even make reactors yet.
Perhaps the payout from disassembly should be modified by how much of the part you disassemble. Stops us at zero components instead of negatives, pays out the same amount whether the whole unit in one disassembly, or across multiple smaller disassembles, and still allows moving large components incrementally as needed.