If the initial connection attempt fails (e.g. server returns 403 over
IPv6), retry with tcp4 to force IPv4. This handles cases where DNS
returns AAAA records but the server isn't properly configured on IPv6.
Fix 1: Limit inbound job payload size to 4MB to prevent OOM from malicious server
Fix 2: Worker pool submit accepts context and returns bool, prevents blocking event loop
Fix 3: Panic recovery in worker pool goroutines prevents permanent worker death
Fix 4: WebSocket handshake timeout (30s) prevents indefinite blocking on slow server
Fix 5: Writer goroutine propagates errors to main loop via writeErrCh
Build the entire frame (header + mask key + masked payload) in one
buffer and write it with a single syscall instead of two separate
writes. Removes the failOnNthWrite test that tested the old
two-write implementation detail.
Wrap the WebSocket connection in an 8KB bufio.Reader so that small
reads (2-byte frame headers, length extensions) are served from
buffer instead of making individual syscalls.
