fix(webui): show quoted context after follow-up send (#5071)

webui/src/lib/user-message-quote.ts

@@ -0,0 +1,58 @@
+interface ParsedUserMessageQuote {
+  quotedContext: string | null;
+  content: string;
+}
+
+const QUOTED_CONTEXT_MARKER = "> [!QUOTE]";
+
+function normalizeNewlines(value: string): string {
+  return value.replace(/\r\n?/g, "\n");
+}
+
+export function formatQuotedUserMessage(content: string, quotedContext?: string | null): string {
+  const body = content.trim();
+  const quote = normalizeNewlines(quotedContext ?? "").trim();
+  if (!quote || body.startsWith("/")) return body;
+
+  const blockquote = quote
+    .split("\n")
+    .map((line) => line ? `> ${line}` : ">")
+    .join("\n");
+  const quotedMessage = `${QUOTED_CONTEXT_MARKER}\n${blockquote}`;
+  return body ? `${quotedMessage}\n\n${body}` : quotedMessage;
+}
+
+export function parseQuotedUserMessage(content: string): ParsedUserMessageQuote {
+  if (!content.startsWith(QUOTED_CONTEXT_MARKER)) {
+    return { quotedContext: null, content };
+  }
+  const normalized = normalizeNewlines(content);
+  const quoteStart = QUOTED_CONTEXT_MARKER.length + 1;
+  if (!normalized.startsWith(`${QUOTED_CONTEXT_MARKER}\n`)) {
+    return { quotedContext: null, content };
+  }
+  const separatorIndex = normalized.indexOf("\n\n", quoteStart);
+  const quoteBlock =
+    separatorIndex === -1
+      ? normalized.slice(quoteStart)
+      : normalized.slice(quoteStart, separatorIndex);
+  const quoteLines = quoteBlock.split("\n");
+  if (
+    quoteLines.length === 0
+    || quoteLines.some((line) => line !== ">" && !line.startsWith("> "))
+  ) {
+    return { quotedContext: null, content };
+  }
+
+  const quotedContext = quoteLines
+    .map((line) => line === ">" ? "" : line.slice(2))
+    .join("\n")
+    .trim();
+  if (!quotedContext) {
+    return { quotedContext: null, content };
+  }
+  return {
+    quotedContext,
+    content: separatorIndex === -1 ? "" : normalized.slice(separatorIndex + 2),
+  };
+}