Perf: pool one-shot SFX + authored VFX, cut per-frame presentation allocation

Track B. All 21 one-shot cues funnelled through FeedbackFx.PlayClip ->
AudioSource.PlayClipAtPoint, which allocates a GameObject + AudioSource per call
and schedules a delayed Destroy — ~20-33 times a second in light combat. New
OneShotAudioPool is a 32-voice 3D ring behind an UNCHANGED PlayClip signature, so
all 20 consuming call sites are untouched.

Parity is the whole game here: PlayClipAtPoint sets spatialBlend = 1 explicitly (a
fresh AudioSource is 2D) and leaves the rest at stock defaults. Two deliberate
divergences, both forced by the voices being long-lived: playOnAwake = false, and
dopplerLevel = 0 because a pooled voice TELEPORTS between events and would
otherwise pitch-bend. Root is DontDestroyOnLoad (WorldLauncher does
LoadScene(Single) while the client world is alive) with a SubsystemRegistration
reset, or session two rents destroyed voices.

Authored impact VFX are pooled per prefab instead of Instantiate/Destroy per hit:
components cached per INSTANCE (refs are instance-scoped), main.stopAction forced
to None (a prefab set to Destroy silently drains the pool), instances filled under
an inactive root so Awake/Start never run — which is what makes the DestroyImmediate
in StripCosmetic safe — ps.Clear before Play, TrailRenderer.Clear after the
reposition, and a Rented flag as the at-most-once guard against a double Return
aliasing one instance to two callers.

Per-frame allocation: the slash-arc and enemy-wedge mesh builders each allocated
four arrays on every call (up to twice a frame, and once per winding enemy); HUD
and ability-bar labels rebuilt their strings every frame; damage-number fades
rewrote TextMesh vertex colours every frame; health bars pushed uGUI writes
unconditionally; two systems played back an empty EntityCommandBuffer (a
structural-change sync point) every frame.

Also closes an AudioClip leak across all seven clip-owning systems: an
AudioClip.Create'd clip is a standalone UnityEngine.Object, so destroying a
system's FX root left it alive (MusicSystem ~6.8 MB, AmbientAudioSystem ~2 MB per
client-world teardown).

CombatFeedbackSystem's TryHold call sites go with this commit because they share
the file; the camera-side removal lands in the next one.

Verified live: PlayClipAtPoint's "One shot audio" GameObject never appears again
across 270 frames of combat with kills; the VFX pool fills to its retain cap and
stabilises; real cues route through the ring. 304/304 EditMode green.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Assets/_Project/Scripts/Client/Presentation/EnemyHitFlashSystem.cs

@@ -49,7 +49,10 @@ namespace ProjectM.Client
 
             // Pass 1: discover enemies, ensure each is tracked + its render children carry the override component.
             _seen.Clear();
-            var ecb = new EntityCommandBuffer(Unity.Collections.Allocator.Temp);
+            // Track B: created lazily — it only ever records on a newly-seen enemy, but it used to be built
+            // and played back (a sync point) every single frame.
+            EntityCommandBuffer ecb = default;
+            bool hasEcb = false;
             foreach (var (health, entity) in
                      SystemAPI.Query<RefRO<Health>>().WithAny<EnemyTag, PlayerTag>().WithAll<LinkedEntityGroup>().WithEntityAccess())
             {
@@ -64,13 +67,17 @@ namespace ProjectM.Client
                     if (!EntityManager.Exists(c) || !EntityManager.HasComponent<MaterialMeshInfo>(c)) continue;
                     entry.RenderKids.Add(c);
                     if (!EntityManager.HasComponent<URPMaterialPropertyBaseColor>(c))
+                    {
+                        if (!hasEcb) { ecb = new EntityCommandBuffer(Unity.Collections.Allocator.Temp); hasEcb = true; }
                         ecb.AddComponent(c, new URPMaterialPropertyBaseColor { Value = White });
+                    }
                 }
                 // Render children can lag ghost instantiation a frame; only finalize once we actually found them (else retry next frame).
                 if (entry.RenderKids.Count > 0) _tracked[entity] = entry;
             }
-            ecb.Playback(EntityManager);
-            ecb.Dispose();
+            // Only pay the structural-change sync point on the frames that actually recorded something
+            // (i.e. a newly-seen enemy) instead of every frame.
+            if (hasEcb) { ecb.Playback(EntityManager); ecb.Dispose(); }
 
             // Pass 2: edge-detect Health, drive + decay the flash, write _BaseColor to the render children.
             var bc = FeelConfig.BodyFlashColor;