feat(audio): Campaign A slice A3 — the server sound channel (0xF750)

acdream never parsed retail's Sound event, so every server-driven cue was
silent: melee hits and wounds, wield/unwield, pickup/drop, lockpicking,
lifestone bind, spell resist, trap triggers, item mana depletion.

SoundEvent parses the 16-byte message (guid, SoundType, f32 volume) whose
layout three oracles agree on: retail CM_Physics::DispatchSB_SoundEvent
@0x006AC760 reading buf+4/+8/+0xC, ACE's GameMessageSound at declared
length 16, and holtburger's PlaySoundData.

Playback reuses EntityEffectController's existing per-guid queue rather
than adding a second one, because retail routes sounds through the SAME
CObjectMaint blob queue as F754/F755: an event for a guid the client does
not know yet is parked and drained by HandleCreateObject, so a creature
that spawns and immediately grunts still grunts. Dropping it — the
obvious alternative — would silently lose the cue. Sound joins Direct and
Typed as a third PendingEffect kind so one readiness edge releases the
whole mixed stream in order.

AudioHookSink.PlayServerSound reproduces two decoded asymmetries with the
animation-hook path: the sound plays at the WIRE volume and the
SoundTable entry's volume is ignored (the hook path does the opposite),
while the entry's probability still gates it and its priority still
drives eviction. An object with no SoundTable plays nothing, matching
CPhysicsObj::play_sound @0x0050F460's early return.

The no-window host parses and discards, exactly as it does for F754/F755
— sound is presentation.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/AcDream.Core.Net/Messages/SoundEvent.cs

@@ -0,0 +1,41 @@
+using System.Buffers.Binary;
+
+namespace AcDream.Core.Net.Messages;
+
+/// <summary>
+/// Retail <c>Sound</c> game message (<c>0xF750</c>): the server tells the client
+/// to play one <c>SoundType</c> slot from an object's SoundTable.
+///
+/// <para>
+/// Wire layout, 16 bytes, S→C — three oracles agree:
+/// <c>u32 opcode | u32 guid | u32 SoundType | f32 volume</c>. Retail dispatch is
+/// <c>CM_Physics::DispatchSB_SoundEvent</c> @ <c>0x006AC760</c> (which reads
+/// <c>buf+4</c>, <c>buf+8</c>, <c>buf+0xC</c>); ACE writes exactly those fields
+/// in <c>GameMessageSound.cs</c> with a declared length of 16; holtburger's
+/// <c>PlaySoundData</c> parses the same triple.
+/// </para>
+///
+/// <para>
+/// This message carries every server-driven cue: melee hits and wounds, wield
+/// and unwield, pickup and drop, lockpicking, lifestone bind, spell resist,
+/// trap triggers, item mana depletion. It was unhandled by acdream until
+/// Campaign A slice A3, which is why all of those were silent.
+/// </para>
+/// </summary>
+public readonly record struct SoundEvent(uint Guid, uint SoundType, float Volume)
+{
+    public const uint Opcode = 0xF750u;
+    public const int WireSize = 16;
+
+    public static SoundEvent? TryParse(ReadOnlySpan<byte> body)
+    {
+        if (body.Length < WireSize
+            || BinaryPrimitives.ReadUInt32LittleEndian(body) != Opcode)
+            return null;
+
+        return new SoundEvent(
+            BinaryPrimitives.ReadUInt32LittleEndian(body[4..]),
+            BinaryPrimitives.ReadUInt32LittleEndian(body[8..]),
+            BinaryPrimitives.ReadSingleLittleEndian(body[12..]));
+    }
+}