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.
