Either each Warp Point would have a flag for "covered by Tachyon beams" or the check would just happen when the ships want to move, and if they appear trapped they would wait to try again in 5 minutes or whatever. I'd probably go with a 2-pass check: Is the wormhole itself covered? If so, wait 5 minutes and try again. If not, select a random path from the system edge to the wormhole. If that path is Tachyon free leave the system to where ever the cloaked ships are converging by circling the outer system edge to reach their exit path. If the exit path is blocked, check another few paths and eventually default to waiting 5 more minutes.