fix: address PR #200 review issues

- Restore PROTOCOL_VERSION to a forward-compatible 2.1.0 and document wire format
- Add NULL guard to config_delete
- Add pipeline cancellation flag and cancellation-aware queue helper
- Join running threads before destroying pipeline contexts on creation failure
- Fix NULL dereference and memory leaks in manifest/chunk handling
- Fix TLS/TCP socket fd leak on connect error paths
- Add compression-level range validation (1-22)
- Close previous log file before opening a new one
- Use getline for unbounded pattern-file lines
- Fix thread-unsafe localtime() and add log level bounds check
- Fix file_load_data to clean up data on read size mismatch
- Add hard ceiling to decompression buffer growth
- Fix mkdir_r bounds check and restore glob comments
- Add send_str NULL guard and mutex-protect bandwidth limiter
- Update AGENTS.md for per-thread io_ssl contract

src/shared/protocol.c

@@ -6,6 +6,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <threads.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -20,6 +21,8 @@ static __thread SSL* io_ssl;
 static unsigned long long io_bwlimit = 0;
 static long long bw_tokens = 0;
 static struct timespec bw_last_refill = {0, 0};
+static mtx_t bw_mutex;
+static once_flag bw_mutex_once = ONCE_FLAG_INIT;
 
 static __thread unsigned long long total_allocated_bytes = 0;
 
@@ -28,15 +31,24 @@ void io_set_fds(int read_fd, int write_fd) {
   io_write_fd = write_fd;
 }
 
+static void bw_mutex_init(void) {
+  mtx_init(&bw_mutex, mtx_plain);
+}
+
 void io_set_bwlimit(unsigned long long bytes_per_sec) {
+  call_once(&bw_mutex_once, bw_mutex_init);
+  mtx_lock(&bw_mutex);
   io_bwlimit = bytes_per_sec;
   bw_tokens = (long long)io_bwlimit;
   clock_gettime(CLOCK_MONOTONIC, &bw_last_refill);
+  mtx_unlock(&bw_mutex);
 }
 
 static void bw_throttle(size_t bytes_written) {
   if (io_bwlimit == 0)
     return;
+  call_once(&bw_mutex_once, bw_mutex_init);
+  mtx_lock(&bw_mutex);
 
   struct timespec now;
   clock_gettime(CLOCK_MONOTONIC, &now);
@@ -61,6 +73,7 @@ static void bw_throttle(size_t bytes_written) {
     bw_tokens = 0;
     clock_gettime(CLOCK_MONOTONIC, &bw_last_refill);
   }
+  mtx_unlock(&bw_mutex);
 }
 
 void io_set_ssl(SSL* ssl) {
@@ -177,6 +190,8 @@ static const char* status_to_string(Status status) {
 }
 
 bool send_str(int file_descriptor, const char* data) {
+  if (data == NULL)
+    return false;
   size_t size = strlen(data);
   if (!send_n_data(file_descriptor, &size, sizeof(size_t)))
     return false;