Prevent partial smellers from detecting cloaked entities (#5557)

## Short description
<!-- What do you propose to change with your PR? -->
Make partial smellers (vulpkanins) unable to detect cloaked entities
using stealth.
This was an unintended feature for partial smellers.

## Why we need to add this
<!-- What is the reason for adding these changes? Please post links to
Discussions as well as Bug Reports here. Please describe how this will
change the game balance. -->
The scent system was designed to do things _**like**_ catching cloaked
entities. I want scent perception to be a strong pull to the future K9
implementation.
However, giving this to vulps has presented periodic balance concerns
when it comes to this.
Recently, I've noticed umbrae vampires and other cloaked antags being
immediately outed by their scent trail by vulpkanin security. That's not
exactly what we want out of the scent system. It's okay for the K9 to do
because there's gonna be like one of them and their ability set will be
limited. But for anyone to roll vulp and invalidate the entire stealth
kit is unhealthy.

## Media (Video/Screenshots)
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of the changes.
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https://github.com/user-attachments/assets/db09283d-519c-474f-8655-c3ed46391450


## Checks
<!-- check boxes for faster reviewing of your PR -->

- [X] I do not require assistance to complete the PR.
- [X] Before posting/requesting review of a PR, I have verified that the
changes work.
- [X] I have added screenshots/videos of the changes, or this PR does
not change in-game mechanics.
- [X] I affirm that my changes are licensed under the [MIT
License](https://github.com/ss14Starlight/space-station-14/blob/Starlight/LICENSE.TXT)
and grant permission for use in this repository under its conditions.

**Changelog**
:cl: Sparlight
- tweak: Partial smellers (vulpkanins) can no longer detect scent
emissions from cloaked entities.
<!--
If you want the players to know about changes made in this PR, specify
them using the template outside the comment. Short and informative.

:cl: STARLIGHT TEAM
- add: Added Starlight.
- remove: Removed SS13.
- tweak: Changed SS14.
- fix: Fixed Rinary.
-->

Author: Sparlight

Content.Client/_Starlight/Scent/Systems/ScentTrackingSystem.cs

@@ -123,9 +123,10 @@ private void ApplyFilter(Entity<ScentMarkerComponent> ent, SmellerComponent smel
             return;
 
         var visible = !IsPerceptionBlocked(smeller) &&
-                      !(smeller.Perception == ScentPerception.Partial && ent.Comp.ContainedIn != null && !ent.Comp.WasDead) &&
-                      !(smeller.Perception == ScentPerception.Partial && IsOutsideOwnEnclosure(ent, enclosure)) &&
-                      (smeller.TrackedScentId == null || ent.Comp.ScentId == smeller.TrackedScentId);
+                        !(smeller.Perception == ScentPerception.Partial && ent.Comp.WasCloaked) &&
+                        !(smeller.Perception == ScentPerception.Partial && ent.Comp.ContainedIn != null && !ent.Comp.WasDead) &&
+                        !(smeller.Perception == ScentPerception.Partial && IsOutsideOwnEnclosure(ent, enclosure)) &&
+                        (smeller.TrackedScentId == null || ent.Comp.ScentId == smeller.TrackedScentId);
         _sprite.SetVisible((ent.Owner, sprite), visible);
     }
 

Content.Server/_Starlight/Scent/Systems/ScentSystem.cs

@@ -24,6 +24,8 @@
 using Content.Shared.Nutrition.EntitySystems;
 using Content.Shared.Popups;
 using Content.Shared.Storage.Components;
+using Content.Shared.Stealth;
+using Content.Shared.Stealth.Components;
 using Content.Shared.Tag;
 using Content.Shared.Verbs;
 using Content.Shared.Zombies;
@@ -36,20 +38,21 @@
 
 namespace Content.Server._Starlight.Scent.Systems;
 
-public sealed class ScentSystem : SharedScentSystem
+public sealed partial class ScentSystem : SharedScentSystem
 {
-    [Dependency] private readonly IRobustRandom _random = default!;
-    [Dependency] private readonly IGameTiming _timing = default!;
-    [Dependency] private readonly SharedEyeSystem _eye = default!;
-    [Dependency] private readonly SharedUserInterfaceSystem _ui = default!;
-    [Dependency] private readonly DoAfterSystem _doAfterSystem = default!;
-    [Dependency] private readonly PopupSystem _popup = default!;
-    [Dependency] private readonly SharedAudioSystem _audio = default!;
-    [Dependency] private readonly SharedTransformSystem _transform = default!;
-    [Dependency] private readonly IPrototypeManager _prototype = default!;
-    [Dependency] private readonly AtmosphereSystem _atmosphere = default!;
-    [Dependency] private readonly InventorySystem _inventory = default!;
-    [Dependency] private readonly TagSystem _tags = default!;
+    [Dependency] private IRobustRandom _random = default!;
+    [Dependency] private IGameTiming _timing = default!;
+    [Dependency] private SharedEyeSystem _eye = default!;
+    [Dependency] private SharedUserInterfaceSystem _ui = default!;
+    [Dependency] private DoAfterSystem _doAfterSystem = default!;
+    [Dependency] private PopupSystem _popup = default!;
+    [Dependency] private SharedAudioSystem _audio = default!;
+    [Dependency] private SharedTransformSystem _transform = default!;
+    [Dependency] private IPrototypeManager _prototype = default!;
+    [Dependency] private AtmosphereSystem _atmosphere = default!;
+    [Dependency] private InventorySystem _inventory = default!;
+    [Dependency] private TagSystem _tags = default!;
+    [Dependency] private SharedStealthSystem _stealth = default!;
 
     private const string ScentMarkerPrototype = "ScentMarker";
     private const int ScentIdByteLength = 8;
@@ -170,7 +173,7 @@ private void OnSniffMenuClosed(Entity<SmellerComponent> ent, ref BoundUIClosedEv
 
     private void OnSmellerMove(Entity<SmellerComponent> ent, ref MoveEvent args)
     {
-        if (ent.Comp.SniffTarget is not { } target || !TryComp<TransformComponent>(target, out var targetXform))
+        if (ent.Comp.SniffTarget is not { } target || !TryComp(target, out TransformComponent? targetXform))
             return;
 
         if (_transform.InRange(args.NewPosition, targetXform.Coordinates, ent.Comp.SniffRange))
@@ -181,17 +184,15 @@ private void OnSmellerMove(Entity<SmellerComponent> ent, ref MoveEvent args)
     }
 
     // Zombies shouldn't be able to hunt survivors by scent.
-    private void OnSmellerZombified(Entity<SmellerComponent> ent, ref EntityZombifiedEvent args)
-    {
+    private void OnSmellerZombified(Entity<SmellerComponent> ent, ref EntityZombifiedEvent args) =>
         RemComp<SmellerComponent>(ent.Owner);
-    }
 
     private void OnTrackMessage(EntityUid uid, SmellerComponent component, ScentSniffTrackMessage args)
     {
         if (component.SniffTarget is not { } target || !Exists(target))
             return;
 
-        if (!TryComp<TransformComponent>(uid, out var xform) || !TryComp<TransformComponent>(target, out var targetXform))
+        if (!TryComp(uid, out TransformComponent? xform) || !TryComp(target, out TransformComponent? targetXform))
             return;
 
         if (!_transform.InRange(xform.Coordinates, targetXform.Coordinates, component.SniffRange))
@@ -420,7 +421,7 @@ public override void Update(float frameTime)
 
             scent.NextEmitTime = now + RollEmitDelay(scent);
 
-            if (TryComp<TransformComponent>(uid, out var xform))
+            if (TryComp(uid, out TransformComponent? xform))
                 EmitScent((uid, scent, xform), scentId);
         }
     }
@@ -466,6 +467,7 @@ private void EmitScent(Entity<ScentComponent, TransformComponent> ent, string sc
         markerComp.TotalDuration = decayTime;
         markerComp.ContainedIn = GetAirtightContainer(xform);
         markerComp.WasDead = MobState.IsDead(uid);
+        markerComp.WasCloaked = IsCloaked(uid);
         Dirty(marker, markerComp);
 
         var despawn = Comp<TimedDespawnComponent>(marker);
@@ -497,7 +499,7 @@ private bool IsSealed(EntityUid uid)
             if (TryComp<EntityStorageComponent>(parent, out var storage) && storage.Airtight)
                 return parent;
 
-            if (!TryComp<TransformComponent>(parent, out var parentXform))
+            if (!TryComp(parent, out TransformComponent? parentXform))
                 break;
 
             parent = parentXform.ParentUid;
@@ -506,17 +508,20 @@ private bool IsSealed(EntityUid uid)
         return null;
     }
 
+    // Same threshold the game already uses to decide an entity is too hidden to examine
+    // (StealthComponent.ExamineThreshold), reused here instead of picking a new cutoff.
+    private bool IsCloaked(EntityUid uid) =>
+        TryComp<StealthComponent>(uid, out var stealth) &&
+        stealth.Enabled &&
+        _stealth.GetVisibility(uid, stealth) <= stealth.ExamineThreshold;
+
     // Suppressed everywhere in the gas pipe network except at a terminus (vent/scrubber), where
     // the scent is genuinely reaching open air.
-    private bool IsHiddenVentCrawl(EntityUid uid)
-    {
-        if (!TryComp<BeingVentCrawlComponent>(uid, out var ventCrawl))
-            return false;
-
-        return !TryComp<VentCrawlHolderComponent>(ventCrawl.Holder, out var holder) ||
-               holder.CurrentTube is not { } tube ||
-               !HasComp<VentCrawlEntryComponent>(tube);
-    }
+    private bool IsHiddenVentCrawl(EntityUid uid) =>
+        TryComp<BeingVentCrawlComponent>(uid, out var ventCrawl) &&
+        (!TryComp<VentCrawlHolderComponent>(ventCrawl.Holder, out var holder) ||
+        holder.CurrentTube is not { } tube ||
+        !HasComp<VentCrawlEntryComponent>(tube));
 
     // Only merges into our own chain tail, never any other nearby marker. Revisiting an old spot
     // would otherwise rewrite the trail's visit order.
@@ -526,7 +531,7 @@ private bool TryMergeIntoExisting(Entity<ScentComponent, TransformComponent> ent
 
         if (scent.LastMarkerEntity is not { } tail ||
             !TryComp<ScentMarkerComponent>(tail, out var marker) ||
-            !TryComp<TransformComponent>(tail, out var tailXform))
+            !TryComp(tail, out TransformComponent? tailXform))
         {
             return false;
         }
@@ -541,6 +546,7 @@ private bool TryMergeIntoExisting(Entity<ScentComponent, TransformComponent> ent
         marker.TotalDuration = decayTime;
         marker.ContainedIn = GetAirtightContainer(xform);
         marker.WasDead = MobState.IsDead(uid);
+        marker.WasCloaked = IsCloaked(uid);
         Dirty(tail, marker);
 
         if (TryComp<TimedDespawnComponent>(tail, out var despawn))

Content.Shared/_Starlight/Scent/Components/ScentMarkerComponent.cs

@@ -21,7 +21,8 @@ public sealed partial class ScentMarkerComponent : Component
     public TimeSpan ExpiresAt;
 
     /// <summary>
-    // How pooled this marker is, 0-1. Maps to alpha/scale client-side.
+    /// How pooled this marker is, 0-1. Maps to alpha/scale client-side.
+    /// </summary>
     /// </summary>
     [DataField, AutoNetworkedField]
     public float Strength;
@@ -44,4 +45,10 @@ public sealed partial class ScentMarkerComponent : Component
     /// </summary>
     [DataField, AutoNetworkedField]
     public bool WasDead;
+    /// <summary>
+    /// Whether the emitter was cloaked (StealthComponent, hidden past its ExamineThreshold) at
+    /// the moment of this emission.
+    /// </summary>
+    [DataField, AutoNetworkedField]
+    public bool WasCloaked;
 }