fix(markdown): require double-tilde strikethrough delimiters

packages/tui/src/components/markdown.ts

@@ -1,8 +1,32 @@
-import { marked, type Token } from "marked";
+import { Marked, type Token, Tokenizer, type Tokens } from "marked";
 import { isImageLine } from "../terminal-image.js";
 import type { Component } from "../tui.js";
 import { applyBackgroundToLine, visibleWidth, wrapTextWithAnsi } from "../utils.js";
 
+const STRICT_STRIKETHROUGH_REGEX = /^(~~)(?=[^\s~])((?:\\.|[^\\])*?(?:\\.|[^\s~\\]))\1(?=[^~]|$)/;
+
+class StrictStrikethroughTokenizer extends Tokenizer {
+	override del(src: string): Tokens.Del | undefined {
+		const match = STRICT_STRIKETHROUGH_REGEX.exec(src);
+		if (!match) {
+			return undefined;
+		}
+
+		const text = match[2];
+		return {
+			type: "del",
+			raw: match[0],
+			text,
+			tokens: this.lexer.inlineTokens(text),
+		};
+	}
+}
+
+const markdownParser = new Marked();
+markdownParser.setOptions({
+	tokenizer: new StrictStrikethroughTokenizer(),
+});
+
 /**
  * Default text styling for markdown content.
  * Applied to all text unless overridden by markdown formatting.
@@ -112,7 +136,7 @@ export class Markdown implements Component {
 		const normalizedText = this.text.replace(/\t/g, "   ");
 
 		// Parse markdown to HTML-like tokens
-		const tokens = marked.lexer(normalizedText);
+		const tokens = markdownParser.lexer(normalizedText);
 
 		// Convert tokens to styled terminal output
 		const renderedLines: string[] = [];