From b1a21760cbc11d9ae28cd1426a72fd18a3a62a77 Mon Sep 17 00:00:00 2001
From: ilanis <ilanis@fireblocks.com>
Date: Tue, 23 Jun 2026 12:03:45 +0300
Subject: [PATCH] fix: drain OSC response when cursor position reply arrives
 first

In some terminals (iTerm2, Terminal.app on macOS) the cursor position
response to CSI 6n arrives before the OSC 11 background-color response.
termStatusReport detected a non-OSC reply and returned early, but
re-enabled TTY echo (via the deferred raw-mode restore) before the OSC
response had arrived. The OSC response then arrived with echo ON and was:

  1. echoed directly to the terminal display as garbled output, and
  2. left in the shell's input buffer, appearing as a phantom shell command
     after the process exited.

Fix: when the first response is not an OSC reply, poll for up to 100 ms
for a pending OSC response and drain it (including the trailing backslash
of the ESC-backslash string terminator) before returning ErrStatusReport.
The 100 ms window is generous enough for the response to arrive over a
local Unix PTY without adding noticeable latency on terminals that truly
don't support OSC 11.

Reproducer: any program that calls HasDarkBackground() during package
init (e.g. charmbracelet/bubbletea v1 does this in tea_init.go) while
running in iTerm2 or Terminal.app.
---
 termenv_unix.go | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/termenv_unix.go b/termenv_unix.go
index bef49ca..9a0875f 100644
--- a/termenv_unix.go
+++ b/termenv_unix.go
@@ -277,8 +277,23 @@ func (o Output) termStatusReport(sequence int) (string, error) {
 		return "", fmt.Errorf("%s: %s", ErrStatusReport, err)
 	}
 
-	// if this is not OSC response, then the terminal does not support it
+	// if this is not OSC response, then the cursor position response arrived first.
+	// The terminal may still send the OSC response; drain it so it doesn't leak
+	// into the TTY buffer and appear as garbage output or a phantom shell command.
 	if !isOSC {
+		if tty := o.TTY(); tty != nil {
+			fd := int(tty.Fd())
+			tv := unix.NsecToTimeval(int64(100 * time.Millisecond))
+			var rfds unix.FdSet
+			rfds.Set(fd)
+			if n, _ := unix.Select(fd+1, &rfds, nil, nil, &tv); n > 0 {
+				drained, _, _ := o.readNextResponse()
+				// readNextResponse stops at ESC (first byte of ST = ESC+\); consume the trailing \.
+				if strings.HasSuffix(drained, string(ESC)) {
+					_, _ = o.readNextByte()
+				}
+			}
+		}
 		return "", ErrStatusReport
 	}