fix(coding-agent/tui): fixed background color stability in output blocks with SGR reset sequences

- Fixed background color stability in output blocks when inner content contains SGR reset sequences, preventing background color from being cleared mid-line.

packages/coding-agent/CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## [Unreleased]
+
 ### Added
 
 - Added resumption hint printed to stderr on session exit showing command to resume the session (e.g., `Resume this session with claude --resume <session-id>`)
@@ -78,6 +79,7 @@
 
 ### Fixed
 
+- Fixed background color stability in output blocks when inner content contains SGR reset sequences, preventing background color from being cleared mid-line
 - Fixed spurious ellipsis appended to output lines that were already padded to terminal width by trimming trailing spaces before truncation check
 - Fixed config file parsing to properly handle missing files instead of treating them as errors
 - Fixed truncation indicator in truncate tool to use ellipsis character (…) instead of verbose '[truncated]' suffix

packages/coding-agent/src/tui/output-block.ts

@@ -32,7 +32,18 @@ export function renderOutputBlock(options: OutputBlockOptions, theme: Theme): st
 					? "accent"
 					: "dim";
 	const border = (text: string) => theme.fg(borderColor, text);
-	const bgFn = state && applyBg ? (text: string) => theme.bg(getStateBgColor(state), text) : undefined;
+	const bgFn = (() => {
+		if (!state || !applyBg) return undefined;
+		const bgAnsi = theme.getBgAnsi(getStateBgColor(state));
+		// Keep block background stable even if inner content contains SGR resets (e.g. "\x1b[0m"),
+		// which would otherwise clear the outer background mid-line.
+		return (text: string) => {
+			const stabilized = text
+				.replace(/\x1b\[(?:0)?m/g, m => `${m}${bgAnsi}`)
+				.replace(/\x1b\[49m/g, m => `${m}${bgAnsi}`);
+			return `${bgAnsi}${stabilized}\x1b[49m`;
+		};
+	})();
 
 	const buildBarLine = (leftChar: string, rightChar: string, label?: string, meta?: string): string => {
 		const left = border(`${leftChar}${cap}`);