fix(syntax): stop swallowing literal backslashes in attribute values

readQuoted treated \X as an escape for any X, so a single literal
backslash in any quoted attribute value was silently dropped
(data-path="C:\Users" parsed as C:Users) and a doubled backslash
collapsed to one. Only the delimiter and the backslash itself are
escapes now; every other backslash is a literal character.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/syntax/src/parser.ts

@@ -1022,12 +1022,13 @@ export function parseHtmlView(src: string, pos: number): { nodes: ViewNode[]; en
     const quote = src[i];
     if (quote !== '"' && quote !== "'") return fail("Expected a quoted attribute value");
     i++;
-    // Backslash-escapes the delimiter (and anything else) so an attribute
-    // value -- e.g. an `api="fn({ a: \"b\" })"` call expression -- can carry
-    // the same quote character it's wrapped in.
+    // Backslash escapes the delimiter -- so an attribute value such as the
+    // call expression `api="fn({ a: \"b\" })"` can carry the same quote
+    // character it's wrapped in -- and escapes itself. Every other backslash
+    // is a literal one, so a value like "C:\Users\name" survives intact.
     let value = "";
     while (i < src.length && src[i] !== quote) {
-      if (src[i] === "\\" && i + 1 < src.length) {
+      if (src[i] === "\\" && (src[i + 1] === quote || src[i + 1] === "\\")) {
         value += src[i + 1];
         i += 2;
         continue;

packages/syntax/test/attribute-escapes.test.ts

@@ -0,0 +1,53 @@
+import { expect, test } from "bun:test";
+import { parse } from "../src/index.ts";
+
+// One literal backslash character. Composing the .wrn sources below by
+// concatenation keeps the escaping unambiguous at a glance.
+const BS = String.fromCharCode(92);
+const Q = '"';
+
+const view = (attr: string) =>
+  `page Esc {\n  view {\n    <main>\n      <div ${attr}>x</div>\n    </main>\n  }\n}\n`;
+
+const attrValue = (source: string): string => {
+  const ast = parse(source) as unknown;
+  const found: string[] = [];
+  const walk = (node: unknown): void => {
+    if (!node || typeof node !== "object") return;
+    if (Array.isArray(node)) {
+      node.forEach(walk);
+      return;
+    }
+    const record = node as Record<string, unknown>;
+    if (typeof record.value === "string" && typeof record.name === "string") {
+      found.push(record.value);
+    }
+    for (const key of Object.keys(record)) walk(record[key]);
+  };
+  walk(ast);
+  return found[found.length - 1] ?? "";
+};
+
+test("a backslash-escaped delimiter becomes a bare quote", () => {
+  // api="fn({ a: \"b\" })"  ->  fn({ a: "b" })
+  const attr = `api=${Q}fn({ a: ${BS}${Q}b${BS}${Q} })${Q}`;
+  expect(attrValue(view(attr))).toBe(`fn({ a: ${Q}b${Q} })`);
+});
+
+test("a doubled backslash collapses to exactly one", () => {
+  // data-x="a\\b"  ->  a\b
+  const attr = `data-x=${Q}a${BS}${BS}b${Q}`;
+  expect(attrValue(view(attr))).toBe(`a${BS}b`);
+});
+
+test("a lone backslash before an ordinary character is preserved", () => {
+  // data-path="C:\Users\name" must survive the lexer intact.
+  const attr = `data-path=${Q}C:${BS}Users${BS}name${Q}`;
+  expect(attrValue(view(attr))).toBe(`C:${BS}Users${BS}name`);
+});
+
+test("a lone backslash before an escape-looking character is preserved verbatim", () => {
+  // data-x="a\nb" is two characters a, backslash, n, b -- not a newline.
+  const attr = `data-x=${Q}a${BS}nb${Q}`;
+  expect(attrValue(view(attr))).toBe(`a${BS}nb`);
+});