Translates the schedules tool's error reasons into messages a worker can act on. Called by YmerNode.Mcp.Tools.Schedules's Wymcp.Tool.handle_error/1.

Every message names the next call rather than describing the fault. The runner's pre-run refusals arrive here too, from add and update, which check a call the way a run would (YmerNode.Scripts.Runner.check/3); those messages already name the script and the action, so each clause adds only where to look next.