chore: import upstream snapshot with attribution

internal/cbm/zstd_store.h

@@ -0,0 +1,25 @@
+#ifndef CBM_ZSTD_STORE_H
+#define CBM_ZSTD_STORE_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+// Zstd compression at specified level (1=fast .. 22=best).
+// Returns compressed size on success, 0 on error.
+int cbm_zstd_compress(const char *src, int srcLen, char *dst, int dstCap, int level);
+
+// Zstd decompression. srcLen/dstCap are size_t so a >2 GiB destination capacity
+// is never truncated (a large DB artifact, or a crafted one, would otherwise
+// wrap through int and desync the real buffer size from the decoder capacity).
+// Returns decompressed size on success (>0), 0 on error.
+int64_t cbm_zstd_decompress(const char *src, size_t srcLen, char *dst, size_t dstCap);
+
+// Declared decompressed content size of a zstd frame (from its header), or 0
+// when unknown/unreadable. Lets the caller size the destination from the frame
+// itself instead of trusting a separate, attacker-controllable size field.
+size_t cbm_zstd_frame_content_size(const char *src, size_t srcLen);
+
+// Maximum compressed size bound for given input size.
+size_t cbm_zstd_compress_bound(int inputSize);
+
+#endif // CBM_ZSTD_STORE_H