perf(compression,tcp): reuse zstd contexts; enable TCP_NODELAY

src/shared/compression.h

@@ -14,4 +14,12 @@ Data* data_decompress_limited(Data* compressed_data, size_t maximum_size);
 bool compression_should_skip(const char* path);
 bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count);
 
+/* Release the calling thread's cached zstd contexts (compressor, decompressor
+ * and scratch buffer).  The cache is thread-local and is also released
+ * automatically when a worker thread exits (via a C11 tss destructor) and for
+ * the main thread at process exit; this explicit entry point exists so tests
+ * and long-lived callers can drop the cache deterministically.  Safe to call
+ * when no context has been created, and idempotent. */
+void compression_free_thread_contexts(void);
+
 #endif