pub const DSR_CURSOR_POSITION_QUERY: &[u8] = b"\x1b[6n";Expand description
Device Status Report cursor-position query — some CLIs (confirmed:
Claude Code, on detecting a real TTY) send this immediately and BLOCK
waiting for the terminal to reply with ESC[<row>;<col>R before
printing anything else at all. A bare portable_pty handle has no
attached terminal emulator to answer this automatically — nothing
does, on any platform, without code specifically watching for it — so
the child hangs forever and the whole capture loop below times out
having seen zero bytes. This is the confirmed root cause of issue
#2429 (“no PTY output captured… despite correct binary resolution”):
isolated repro (a standalone portable_pty harness spawning the exact
same binary/args) showed the child’s first and ONLY output was these
4 bytes, then silence: answering this one query unblocked it
immediately, and it printed its OAuth URL within half a second.