network: close each bsd fd once and drop unwanted or malformed room packets

Two threads closing the same fd both copied the descriptor and both called
Close(), so a host socket could be closed twice, and the second closesocket
could hit an unrelated socket that had reused the host fd. CloseImpl now
frees the slot under file_descriptors_mutex first and only that thread closes
the socket; the other gets EBADF.

OnProxyPacketReceived decompressed every room packet when any fd had a
socket, including native sockets and proxy sockets on other ports. Sockets
now report through AcceptsProxyPacket whether they want a packet, and only
those are collected, so an unwanted packet is not decompressed.

DecompressDataZSTD passed the frame's declared size straight to the vector
constructor, so a malformed or unsized frame from a room member threw on the
room thread. The new TryDecompressDataZSTD rejects invalid, unsized and
oversized frames, and bsd drops such packets with a warning.
DecompressDataZSTD now returns an empty vector for them instead of throwing.

Assisted-by: Claude Opus 5.5 (investigation and implementation)

1 files changed, 5 insertions, 0 deletions

diff --git a/src/core/internal_network/sockets.h b/src/core/internal_network/sockets.h
index 37cffd4651..29b5b0f18a 100644
--- a/src/core/internal_network/sockets.h
+++ b/src/core/internal_network/sockets.h
@@ -89,6 +89,9 @@ public:
 
     virtual bool IsOpened() const = 0;
 
+    /// Whether HandleProxyPacket would queue the packet; checked before decompressing it
+    virtual bool AcceptsProxyPacket(const ProxyPacket& packet) = 0;
+
     /// Queues a room packet whose data is already decompressed
     virtual void HandleProxyPacket(const ProxyPacket& packet) = 0;
 
@@ -164,6 +167,8 @@ public:
 
     bool IsOpened() const override;
 
+    bool AcceptsProxyPacket(const ProxyPacket& packet) override;
+
     void HandleProxyPacket(const ProxyPacket& packet) override;
 
 private: