docs: add heap overflow fix and crash diagnostics to changelog

Author: dvershinin

CHANGELOG.md

@@ -8,8 +8,10 @@ All notable changes to this project will be documented in this file.
 - Dynamic Record Sizing (DRS) for TLS transport — auto-activates on all TLS connections, no flag needed. Record sizes mimic real HTTPS servers (1450→4096→16144 bytes with ±100 noise), making proxy traffic statistically indistinguishable from real HTTPS ([#50](https://github.com/GetPageSpeed/MTProxy/issues/50))
 - E2E test for TLS data-after-handshake burst (validates direct+TLS race condition fix)
 - Standalone DRS E2E test script (`tests/test_drs_e2e.py`) for production verification with Telethon
+- Crash diagnostics: libunwind-based stack traces on Alpine/musl (opt-in via `DEBUG_TOOLS=1` build arg)
 
 ### Fixed
+- **Heap buffer overflow in `mtfront_pre_loop`** — `CONN_INFO()` was used on a listening connection job, writing `window_clamp` at offset 512 into an 80-byte allocation (432 bytes out of bounds). Present in upstream since the initial commit (May 2018), affects all deployments using workers (`-M 1+`). Manifested as intermittent SIGSEGV depending on allocator page alignment
 - Direct mode: race condition where client data was relayed before obfuscated2 init, causing DC rejection
 - Direct mode: missing `check_conn_functions` for `ct_direct_client` caused crash on TLS+direct connections