Shuttles have air again. (ParadiseSS13#27884)

code/controllers/subsystem/SSair.dm

@@ -85,6 +85,9 @@ SUBSYSTEM_DEF(air)
 	/// Are we currently running in a MILLA-safe context, i.e. is is_synchronous *guaranteed* to be TRUE. Nothing outside of this file should change this.
 	VAR_PRIVATE/in_milla_safe_code = FALSE
 
+	/// Are we in MILLA-safe code that can safely sleep?
+	VAR_PRIVATE/safe_to_sleep = FALSE
+
 	/// A list of callbacks waiting for MILLA to finish its tick and enter synchronous mode.
 	var/list/waiting_for_sync = list()
 	var/list/sleepable_waiting_for_sync = list()
@@ -724,16 +727,24 @@ SUBSYSTEM_DEF(air)
 	waiting_for_sync += CB
 
 /// Similar to addtimer, but triggers once MILLA enters synchronous mode. This version allows for sleeping if it's absolutely necessary.
-/datum/controller/subsystem/air/proc/sleepable_synchronize(datum/milla_safe/CB)
+/datum/controller/subsystem/air/proc/sleepable_synchronize(datum/milla_safe_must_sleep/CB)
+	if(safe_to_sleep)
+		var/was_safe = SSair.in_milla_safe_code
+		SSair.in_milla_safe_code = TRUE
+		// This is one of two intended places to call this otherwise-unsafe proc.
+		CB.private_unsafe_invoke()
+		SSair.in_milla_safe_code = was_safe
+		return
+
 	sleepable_waiting_for_sync += CB
 
 /datum/controller/subsystem/air/proc/is_in_milla_safe_code()
 	return in_milla_safe_code
 
 /datum/controller/subsystem/air/proc/on_milla_tick_finished()
-	run_sleepless_callbacks()
 	run_sleeping_callbacks()
 	is_synchronous = TRUE
+	run_sleepless_callbacks()
 
 /datum/controller/subsystem/air/proc/run_sleepless_callbacks()
 	// Just in case someone is naughty and decides to sleep, make sure that this method runs fully anyway.
@@ -748,11 +759,13 @@ SUBSYSTEM_DEF(air)
 
 /datum/controller/subsystem/air/proc/run_sleeping_callbacks()
 	in_milla_safe_code = TRUE
+	safe_to_sleep = TRUE
 	for(var/datum/milla_safe_must_sleep/CB as anything in sleepable_waiting_for_sync)
 		// This is one of two intended places to call this otherwise-unsafe proc.
 		CB.private_unsafe_invoke()
 	sleepable_waiting_for_sync.Cut()
 	in_milla_safe_code = FALSE
+	safe_to_sleep = FALSE
 
 /proc/milla_tick_finished()
 	// Any proc that wants MILLA to be synchronous should not sleep.

code/modules/shuttle/shuttle.dm

@@ -448,12 +448,12 @@
 		if(!canMove())
 			return -1
 
-	var/datum/milla_safe/docking_port_dock/milla = new()
+	var/datum/milla_safe_must_sleep/docking_port_dock/milla = new()
 	milla.invoke_async(src, S1, force, transit)
 
-/datum/milla_safe/docking_port_dock
+/datum/milla_safe_must_sleep/docking_port_dock
 
-/datum/milla_safe/docking_port_dock/on_run(obj/docking_port/mobile/mobile_port, obj/docking_port/stationary/S1, force, transit)
+/datum/milla_safe_must_sleep/docking_port_dock/on_run(obj/docking_port/mobile/mobile_port, obj/docking_port/stationary/S1, force, transit)
 	// Re-check that it's OK to dock.
 	if(S1.get_docked() == mobile_port)
 		mobile_port.remove_ripples()