ios: show markdown files with HTML tags formatted to the end (#8008)

* ios: show markdown files with HTML tags formatted to the end

* ios: show every < in a markdown file as text

---------

Co-authored-by: spacedandy-agents-simplex <342056592+spacedandy-agents-simplex@users.noreply.github.com>

apps/ios/Shared/Views/Chat/ChatItem/MarkdownFileView.swift

@@ -22,9 +22,7 @@ func showMarkdownFile(_ file: CIFile) {
             let data = try getFileData(getAppFilePath(fileSource.filePath), fileSource.cryptoArgs)
             let text = decodedText(data)
             let lines = text.components(separatedBy: "\n")
-            let html = withinMarkdownLimits(lines)
-                ? MarkdownParser(modifiers: [Modifier(target: .html) { escapedHTML($0.markdown) }, imagesWithinBudget()]).html(from: text)
-                : nil
+            let html = withinMarkdownLimits(lines) ? htmlShowingTagsAsText(text) : nil
             let shownLines = lines.flatMap(chunkedLine)
             let hasBidiControls = text.unicodeScalars.contains(where: isBidiControl)
             await MainActor.run {
@@ -57,6 +55,15 @@ private func replacingControlChar(_ s: Unicode.Scalar) -> Unicode.Scalar {
     s.value < 0x20 && s != "\t" && s != "\n" && s != "\r" ? "?" : s
 }
 
+// decodedText replaces control characters, so the text has no U+0001 of its own
+private let lessThanStandIn = "\u{1}"
+
+private func htmlShowingTagsAsText(_ text: String) -> String {
+    MarkdownParser(modifiers: [imagesWithinBudget()])
+        .html(from: text.replacingOccurrences(of: "<", with: lessThanStandIn, options: .literal))
+        .replacingOccurrences(of: lessThanStandIn, with: "&lt;", options: .literal)
+}
+
 private func withinMarkdownLimits(_ lines: [String]) -> Bool {
     var tableRows = 0
     var linkNesting = 0