From c294bc397b6a50fa3e1709246250e8b394555ce1 Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@joshtriplett.org>
Date: Mon, 6 Apr 2026 09:44:03 -0700
Subject: [PATCH] fix(tui): check background color on resume

Problem:
We normally get the background color via continuous reporting. However,
if we were backgrounded while the light/dark mode changed, we won't have
received the report, and we'll have the wrong background color.

Without this change, if you background nvim, toggle the light/dark mode,
resume, and check `:set bg`, it will not match the current state.

Solution:
Query it on resume as well. (This requires separating the query from the
flush, to just do the query along with all the others, while waiting to
flush until we've set up uv.)

With this change, if you background nvim, toggle the light/dark mode,
resume, and check `:set bg`, it will have updated.
---
 runtime/doc/news.txt |  2 ++
 src/nvim/tui/tui.c   | 15 +++++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index 81df75ad6c..4af8dd6716 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -394,6 +394,8 @@ TUI
   sequence.
 • The TUI now renders the SGR dim (faint), blink, conceal, and overline
   attributes.
+• The TUI will re-query the terminal's background color when resuming from
+  a suspended state, and Nvim will update 'background' accordingly.
 
 UI
 
diff --git a/src/nvim/tui/tui.c b/src/nvim/tui/tui.c
index 1cdcf59fec..8eea4fb5b5 100644
--- a/src/nvim/tui/tui.c
+++ b/src/nvim/tui/tui.c
@@ -337,14 +337,20 @@ static void tui_reset_key_encoding(TUIData *tui)
   }
 }
 
+static void tui_query_bg_color_noflush(TUIData *tui)
+  FUNC_ATTR_NONNULL_ALL
+{
+  out(tui, S_LEN("\x1b]11;?\x07\x1b[5n"));
+}
+
 /// Write the OSC 11 + DSR sequence to the terminal emulator to query the current
-/// background color.
+/// background color, and flush the terminal.
 ///
 /// Response will be handled by the TermResponse handler in _core/defaults.lua.
 void tui_query_bg_color(TUIData *tui)
   FUNC_ATTR_NONNULL_ALL
 {
-  out(tui, S_LEN("\x1b]11;?\x07\x1b[5n"));
+  tui_query_bg_color_noflush(tui);
   flush_buf(tui);
 }
 
@@ -483,6 +489,11 @@ static void terminfo_start(TUIData *tui)
   // Query the terminal to see if it supports Kitty's keyboard protocol
   tui_query_kitty_keyboard(tui);
 
+  // Query the terminal's background color. We normally get it via continuous reporting (set via
+  // `kTermModeThemeUpdates` above), but if we were backgrounded while the light/dark mode changed,
+  // we won't have received the report, so we also query it on resume.
+  tui_query_bg_color_noflush(tui);
+
   int ret;
   uv_loop_init(&tui->write_loop);
   if (tui->out_isatty) {