macOS PTY stdin forwarding raises SystemError buffer overflow on key input

[D3f0]

Problem

When running a command through Context.run(..., pty=True) on macOS, keyboard input can terminate Invoke's handle_stdin worker with:

DEBUG Encountered exception SystemError('buffer overflow') in thread for 'handle_stdin'

The issue is reproducible with invoke-toolkit==0.0.68, invoke==3.0.3, and Python 3.14 on macOS. Arrow/function keys are sufficient to trigger it.

Root Cause

invoke.terminals.bytes_to_read() calls fcntl.ioctl(input_, termios.FIONREAD, b" ") when the input reports isatty() == True. On macOS, the ioctl result can exceed the two-byte buffer expected by struct.unpack("h", ...), causing Python to raise SystemError("buffer overflow").

The exception is raised inside Invoke's handle_stdin thread and then logged by the thread exception handler.

Fix

Make the terminal-byte availability probe safe on macOS/POSIX. Possible approaches:

• use a sufficiently sized mutable buffer and unpack the documented result width;
• avoid FIONREAD and read one byte after select() reports readiness; or
• catch/handle the platform-specific ioctl failure and fall back to a one-byte read.

Please add a regression test that exercises bytes_to_read() or handle_stdin with a PTY and keyboard input, including escape-sequence keys.

Temporary downstream workaround: wrap the input stream so isatty() returns False, put the terminal in cbreak mode, and pass it as in_stream; this avoids the FIONREAD branch but should not be necessary for users.

[D3f0]

Closed manually after merge of PR #137, which fixed the macOS PTY stdin buffer overflow and added regression coverage.