Dev Build 2026-09-10 21:28

PTY reader NAPI-style optimization:

• Eliminated yield_now() busy-spin on channel full (blocking send backpressure)
• Fixed drain_data byte budget data-loss at boundary
• Fixed child exit detection (SIGCHLD process-global race)
• Pre-drain before poller wait (wakeup protocol soundness)
• All 146 tests + 6 reader state-machine tests passing