Small auto-observe fixes (#5788)

# About the pull request

Fixes/tweaks a couple of auto-observe things that I noticed after #5751.
Specifically:
- Fixes `runtime error: client_screen_add overridden. Use override =
TRUE to suppress this warning`/`runtime error: client_screen_remove
overridden. Use override = TRUE to suppress this warning`.
*This error was consistently thrown when a ghost who's body is being
observed re-enters their body. `observe_target_new_mind()` tries to
re-register the some signals on the body's new client, but didn't have
the `override` argument set.*

- Stops 'hidden' actions being added to the screen of observing players.
(e.g. the xeno tacmap action if the queen isn't ovied)

- Makes any observers transfer over to the new body when a xenomorph
evolves/de-evolves.
*(I also added `/mob/dead/observer` to the `observers` variable's
declaration since it wasn't particularly clear what the list held.)*

- Fixes the target player's action buttons disappearing for observers if
they reconnect or re-enter their body.
*(The actions were being shown to the player in
`Login()`>`show_hud()`>`update_action_buttons()` before the observer
could re-register signals in `observe_target_login()`.)
In order to fix this I renamed the existing `COMSIG_GLOB_MOB_LOGIN`,
`COMSIG_CLIENT_MOB_LOGIN`, `COMSIG_MOB_LOGIN` signals, and made
`COMSIG_MOB_LOGIN` send a bit earlier in the proc.*

# Explain why it's good for the game

Bugfixes :)


# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
fix: Fixed 'hidden' action buttons being shown to observing players.
qol: Made any observers transfer over when a Xenomorph
evolves/de-evolves.
/:cl:

code/__DEFINES/dcs/signals/atom/mob/signals_mob.dm

@@ -75,9 +75,13 @@
 #define COMSIG_MOB_PRE_CLICK "mob_pre_click"
 	#define COMPONENT_INTERRUPT_CLICK (1<<0)
 
-///from base of /mob/Login(): ()
+/// From base of /mob/Login(), called when a client logs into this mob: ()
+/// Not to be confused with [COMSIG_MOB_LOGGED_IN]
 #define COMSIG_MOB_LOGIN "mob_login"
-///from base of /mob/Logout(): ()
+/// From base of /mob/Login(), called after a client logs into this mob: ()
+/// Not to be confused with [COMSIG_MOB_LOGIN]
+#define COMSIG_MOB_LOGGED_IN "mob_logged_in"
+/// From base of /mob/Logout(): ()
 #define COMSIG_MOB_LOGOUT "mob_logout"
 
 /// From /mob/proc/change_real_name(): (old_name, new_name)

code/__DEFINES/dcs/signals/signals_client.dm

@@ -19,8 +19,8 @@
 /// Called after one or more verbs are added: (list of verbs added)
 #define COMSIG_CLIENT_VERB_REMOVED "client_verb_removed"
 
-/// Called after a client logs into a mob: (mob)
-#define COMSIG_CLIENT_MOB_LOGIN "client_mob_changed"
+/// Called from /mob/Login() after a client logs into a mob: (mob)
+#define COMSIG_CLIENT_MOB_LOGGED_IN "client_mob_logged_in"
 
 /// Called when something is added to a client's screen : /client/proc/add_to_screen(screen_add)
 #define COMSIG_CLIENT_SCREEN_ADD "client_screen_add"

code/__DEFINES/dcs/signals/signals_global.dm

@@ -34,9 +34,11 @@
 
 #define COMSIG_GLOB_REMOVE_VOTE_BUTTON "!remove_vote_button"
 
-#define COMSIG_GLOB_CLIENT_LOGIN "!client_login"
+/// Called from /client/New() when a client logs in to the game: (client)
+#define COMSIG_GLOB_CLIENT_LOGGED_IN "!client_logged_in"
 
-#define COMSIG_GLOB_MOB_LOGIN "!mob_login"
+/// Called from /mob/Login() when a client logs into a mob: (mob)
+#define COMSIG_GLOB_MOB_LOGGED_IN "!mob_logged_in"
 
 ///from /datum/controller/subsystem/ticker/PostSetup
 #define COMSIG_GLOB_POST_SETUP "!post_setup"

code/controllers/subsystem/ticker.dm

@@ -207,7 +207,7 @@ SUBSYSTEM_DEF(ticker)
 	CHECK_TICK
 	mode.announce()
 	if(mode.taskbar_icon)
-		RegisterSignal(SSdcs, COMSIG_GLOB_CLIENT_LOGIN, PROC_REF(handle_mode_icon))
+		RegisterSignal(SSdcs, COMSIG_GLOB_CLIENT_LOGGED_IN, PROC_REF(handle_mode_icon))
 		set_clients_taskbar_icon(mode.taskbar_icon)
 
 	if(GLOB.perf_flags & PERF_TOGGLE_LAZYSS)

code/controllers/subsystem/vote.dm

@@ -59,7 +59,7 @@ SUBSYSTEM_DEF(vote)
 	voting.Cut()
 	remove_action_buttons()
 
-	UnregisterSignal(SSdcs, COMSIG_GLOB_CLIENT_LOGIN)
+	UnregisterSignal(SSdcs, COMSIG_GLOB_CLIENT_LOGGED_IN)
 
 	for(var/c in GLOB.player_list)
 		update_static_data(c)
@@ -373,7 +373,7 @@ SUBSYSTEM_DEF(vote)
 			if(send_clients_vote)
 				C.mob.vote()
 
-		RegisterSignal(SSdcs, COMSIG_GLOB_CLIENT_LOGIN, PROC_REF(handle_client_joining))
+		RegisterSignal(SSdcs, COMSIG_GLOB_CLIENT_LOGGED_IN, PROC_REF(handle_client_joining))
 		SStgui.update_uis(src)
 		return TRUE
 	return FALSE

code/game/objects/items/devices/radio/headset.dm

@@ -233,7 +233,7 @@
 		), PROC_REF(turn_on))
 		wearer = user
 		RegisterSignal(user, COMSIG_MOB_STAT_SET_ALIVE, PROC_REF(update_minimap_icon))
-		RegisterSignal(user, COMSIG_MOB_LOGIN, PROC_REF(add_hud_tracker))
+		RegisterSignal(user, COMSIG_MOB_LOGGED_IN, PROC_REF(add_hud_tracker))
 		RegisterSignal(user, COMSIG_MOB_DEATH, PROC_REF(update_minimap_icon))
 		RegisterSignal(user, COMSIG_HUMAN_SET_UNDEFIBBABLE, PROC_REF(update_minimap_icon))
 		if(headset_hud_on)
@@ -250,7 +250,7 @@
 	UnregisterSignal(user, list(
 		COMSIG_LIVING_REJUVENATED,
 		COMSIG_HUMAN_REVIVED,
-		COMSIG_MOB_LOGIN,
+		COMSIG_MOB_LOGGED_IN,
 		COMSIG_MOB_DEATH,
 		COMSIG_HUMAN_SET_UNDEFIBBABLE,
 		COMSIG_MOB_STAT_SET_ALIVE

code/modules/client/client_procs.dm

@@ -444,7 +444,7 @@ GLOBAL_LIST_INIT(whitelisted_client_procs, list(
 
 	view = GLOB.world_view_size
 
-	SEND_GLOBAL_SIGNAL(COMSIG_GLOB_CLIENT_LOGIN, src)
+	SEND_GLOBAL_SIGNAL(COMSIG_GLOB_CLIENT_LOGGED_IN, src)
 
 	//////////////
 	//DISCONNECT//

code/modules/escape_menu/escape_menu.dm

@@ -49,7 +49,7 @@ GLOBAL_LIST_EMPTY(escape_menus)
 	show_page()
 
 	RegisterSignal(client, COMSIG_PARENT_QDELETING, PROC_REF(on_client_qdel))
-	RegisterSignal(client, COMSIG_CLIENT_MOB_LOGIN, PROC_REF(on_client_mob_login))
+	RegisterSignal(client, COMSIG_CLIENT_MOB_LOGGED_IN, PROC_REF(on_client_mob_login))
 
 	if (!isnull(ckey))
 		GLOB.escape_menus[ckey] = src

code/modules/mob/dead/observer/observer.dm

@@ -236,8 +236,9 @@
 	if(observe_target_client != new_client)
 		observe_target_client = new_client
 
-	RegisterSignal(observe_target_client, COMSIG_CLIENT_SCREEN_ADD, PROC_REF(observe_target_screen_add))
-	RegisterSignal(observe_target_client, COMSIG_CLIENT_SCREEN_REMOVE, PROC_REF(observe_target_screen_remove))
+	// Override the signal from any previous targets.
+	RegisterSignal(observe_target_client, COMSIG_CLIENT_SCREEN_ADD, PROC_REF(observe_target_screen_add), TRUE)
+	RegisterSignal(observe_target_client, COMSIG_CLIENT_SCREEN_REMOVE, PROC_REF(observe_target_screen_remove), TRUE)
 
 /// When the observe target logs in our observer connect to the new client
 /mob/dead/observer/proc/observe_target_login(mob/living/new_character)
@@ -246,8 +247,9 @@
 	if(observe_target_client != new_character.client)
 		observe_target_client = new_character.client
 
-	RegisterSignal(observe_target_client, COMSIG_CLIENT_SCREEN_ADD, PROC_REF(observe_target_screen_add))
-	RegisterSignal(observe_target_client, COMSIG_CLIENT_SCREEN_REMOVE, PROC_REF(observe_target_screen_remove))
+	// Override the signal from any previous targets.
+	RegisterSignal(observe_target_client, COMSIG_CLIENT_SCREEN_ADD, PROC_REF(observe_target_screen_add), TRUE)
+	RegisterSignal(observe_target_client, COMSIG_CLIENT_SCREEN_REMOVE, PROC_REF(observe_target_screen_remove), TRUE)
 
 ///makes the ghost see the target hud and sets the eye at the target.
 /mob/dead/observer/proc/do_observe(atom/movable/target)
@@ -266,6 +268,7 @@
 	client.clear_screen()
 	client.eye = carbon_target
 	observe_target_mob = carbon_target
+
 	carbon_target.auto_observed(src)
 
 	RegisterSignal(src, COMSIG_MOVABLE_MOVED, PROC_REF(observer_move_react))

code/modules/mob/living/carbon/carbon.dm

@@ -431,8 +431,12 @@
 	observers |= observer
 	hud_used.show_hud(hud_used.hud_version, observer)
 
+	// Add the player's action buttons (not the actions themselves) to the observer's screen.
 	for(var/datum/action/action as anything in actions)
-		// Add the action's button (not the action itself) to the observer's screen.
+		// Skip any hidden ones (of course).
+		if(action.hidden || action.player_hidden)
+			continue
+
 		observer.client.add_to_screen(action.button)
 
 //generates realistic-ish pulse output based on preset levels

code/modules/mob/living/carbon/xenomorph/Xenomorph.dm

@@ -766,6 +766,11 @@
 	var/datum/mob_hud/MH = GLOB.huds[MOB_HUD_XENO_INFECTION]
 	MH.add_hud_to(src, src)
 
+// Transfer any observing players over to the xeno's new body (`target`) on evolve/de-evolve.
+/mob/living/carbon/xenomorph/transfer_observers_to(atom/target)
+	for(var/mob/dead/observer/observer as anything in observers)
+		observer.clean_observe_target()
+		observer.do_observe(target)
 
 /mob/living/carbon/xenomorph/check_improved_pointing()
 	//xeno leaders get a big arrow and less cooldown

code/modules/mob/login.dm

@@ -18,6 +18,8 @@
 
 	update_Login_details()
 
+	SEND_SIGNAL(src, COMSIG_MOB_LOGIN)
+
 	client.images = null
 	client.screen = null //remove hud items just in case
 	if(!hud_used)
@@ -58,6 +60,6 @@
 
 	client.init_verbs()
 
-	SEND_GLOBAL_SIGNAL(COMSIG_GLOB_MOB_LOGIN, src)
-	SEND_SIGNAL(client, COMSIG_CLIENT_MOB_LOGIN, src)
-	SEND_SIGNAL(src, COMSIG_MOB_LOGIN)
+	SEND_GLOBAL_SIGNAL(COMSIG_GLOB_MOB_LOGGED_IN, src)
+	SEND_SIGNAL(client, COMSIG_CLIENT_MOB_LOGGED_IN, src)
+	SEND_SIGNAL(src, COMSIG_MOB_LOGGED_IN)

code/modules/mob/mob_defines.dm

@@ -28,7 +28,8 @@
 	I'll make some notes on where certain variable defines should probably go.
 	Changing this around would probably require a good look-over the pre-existing code.
 	*/
-	var/list/observers //The list of people observing this mob.
+	/// The list of people observing this mob.
+	var/list/mob/dead/observer/observers
 	var/zone_selected = "chest"
 
 	var/use_me = 1 //Allows all mobs to use the me verb by default, will have to manually specify they cannot
@@ -429,4 +430,3 @@
 			return
 
 		src.regenerate_icons()
-

code/modules/vehicles/van/van.dm

@@ -83,7 +83,7 @@
 
 	icon_state = null
 
-	RegisterSignal(SSdcs, COMSIG_GLOB_MOB_LOGIN, PROC_REF(add_default_image))
+	RegisterSignal(SSdcs, COMSIG_GLOB_MOB_LOGGED_IN, PROC_REF(add_default_image))
 
 	for(var/I in GLOB.player_list)
 		add_default_image(SSdcs, I)
@@ -125,7 +125,7 @@
 
 	mobs_under += L
 	RegisterSignal(L, COMSIG_PARENT_QDELETING, PROC_REF(remove_under_van))
-	RegisterSignal(L, COMSIG_MOB_LOGIN, PROC_REF(add_client))
+	RegisterSignal(L, COMSIG_MOB_LOGGED_IN, PROC_REF(add_client))
 	RegisterSignal(L, COMSIG_MOVABLE_MOVED, PROC_REF(check_under_van))
 
 	if(L.client)
@@ -141,7 +141,7 @@
 
 	UnregisterSignal(L, list(
 		COMSIG_PARENT_QDELETING,
-		COMSIG_MOB_LOGIN,
+		COMSIG_MOB_LOGGED_IN,
 		COMSIG_MOVABLE_MOVED,
 	))