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

AGENTS.md

@@ -206,7 +206,7 @@ tea pr close <number> --repo TapTap/FastSync
 
 ## Common pitfalls
 
-- **`__thread` on shared SSL context**: io_ssl must NOT be thread-local — worker threads inherit the SSL context from the main thread. Use regular `static SSL* io_ssl`.
+- **Per-thread SSL context**: `io_ssl` is stored per-thread (`static __thread SSL* io_ssl`). Each thread that performs protocol I/O must call `io_set_ssl()` to install its own SSL object before using `send_*` / `receive_*` primitives. The main thread's SSL context is not automatically inherited by worker threads.
 - **SSL WANT_READ/WANT_WRITE retry**: Always retry on `SSL_ERROR_WANT_READ` and `SSL_ERROR_WANT_WRITE` in `send_n_data`/`receive_n_data`. Removing these breaks TLS multithreaded transfers.
 - **clang-format version**: The CI image uses clang-format 18. Always format inside the CI Docker container for exact match.
 - **Merge order matters**: Merge the most comprehensive branch first, then smaller ones, to minimize conflicts when creating a combined branch.