fix(coding-agent): keep syntax colors on multiline tokens (#10356)

* fix(coding-agent): keep syntax colors on multiline tokens

- format each line of a highlighted span separately
- add regression test for python docstrings
- fixes #10143

* fix(coding-agent): use text color for string interpolations

- map highlight.js `subst` scope to text color

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed syntax highlighting losing colors after the first line of multiline strings and comments in fenced code blocks ([#10143](https://github.com/earendil-works/pi/issues/10143))
+
 ## [1.0.3] - 2026-10-05
 
 ### New Features

packages/coding-agent/src/modes/interactive/theme/theme.ts

@@ -966,6 +966,7 @@ function buildCliHighlightTheme(t: Theme): CliHighlightTheme {
 		number: (s: string) => t.fg("syntaxNumber", s),
 		regexp: (s: string) => t.fg("syntaxString", s),
 		string: (s: string) => t.fg("syntaxString", s),
+		subst: (s: string) => t.fg("text", s),
 		comment: (s: string) => t.fg("syntaxComment", s),
 		doctag: (s: string) => t.fg("syntaxComment", s),
 		meta: (s: string) => t.fg("muted", s),

packages/coding-agent/src/utils/syntax-highlight.ts

@@ -155,7 +155,12 @@ export function renderHighlightedHtml(html: string, theme: HighlightTheme = {}):
 			return;
 		}
 		const formatter = getActiveFormatter(scopes, theme);
-		output += formatter ? formatter(textBuffer) : textBuffer;
+		output += formatter
+			? textBuffer
+					.split("\n")
+					.map((line) => (line ? formatter(line) : line))
+					.join("\n")
+			: textBuffer;
 		textBuffer = "";
 	};
 

packages/coding-agent/test/syntax-highlight.test.ts

@@ -1,6 +1,6 @@
 import { resetCapabilitiesCache, setCapabilities } from "@earendil-works/pi-tui";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
-import { highlightCode, initTheme, theme } from "../src/modes/interactive/theme/theme.ts";
+import { getMarkdownTheme, highlightCode, initTheme, theme } from "../src/modes/interactive/theme/theme.ts";
 import {
 	highlight,
 	loadAllHighlightLanguages,
@@ -96,6 +96,23 @@ describe("theme syntax highlighting", () => {
 		resetCapabilitiesCache();
 	});
 
+	// #10143
+	it("colors each line of Python docstrings independently", () => {
+		const code = '"""\nline one\n\nline two\n"""\nafter';
+		const ansi = theme.getFgAnsi("syntaxString");
+		const expected = [
+			`${ansi}"""\x1b[39m`,
+			`${ansi}line one\x1b[39m`,
+			"",
+			`${ansi}line two\x1b[39m`,
+			`${ansi}"""\x1b[39m`,
+			"after",
+		];
+
+		expect(highlightCode(code, "python")).toEqual(expected);
+		expect(getMarkdownTheme().highlightCode?.(code, "python")).toEqual(expected);
+	});
+
 	it("colors diff additions and deletions in fenced diff blocks", () => {
 		const lines = highlightCode("-old\n+new\n", "diff");