See this Comm Center thread by Don Elledge. Prevent starting a Plan with any Observation that would enter the "cone of exclusion" set by the Tilt-Up limit, and also mind the possibility of the derotator hitting it's rotation limits. This should be done in the context of a constraint like the ACP "hard limits" horizon is now, internally to the Scheduler, so it is automatic and does not require any user input. Detect it being an alt-az from ACP settings. For the derotator somehow will need the PABias and the derotator limits???
While you're at it, generalize the tilt-up limits protection for Fork and German mounts as well, prevent the Plan from starting if it would ever put the mount into the exclusion region.