fix(gmail): handle escaped quotes in mailbox list splitting

split_mailbox_list toggled quote state on every `"` without accounting
for backslash-escaped quotes (`\"`), causing display names like
`"Doe \"JD, Sr\""` to split incorrectly at interior commas.

Track `prev_backslash` so `\"` inside quoted strings is treated as a
literal quote character rather than a delimiter toggle. Double
backslashes (`\\`) are handled correctly as well.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: HeroSizy

src/helpers/gmail/reply.rs

@@ -216,10 +216,15 @@ fn split_mailbox_list(header: &str) -> Vec<&str> {
     let mut result = Vec::new();
     let mut in_quotes = false;
     let mut start = 0;
+    let mut prev_backslash = false;
 
     for (i, ch) in header.char_indices() {
         match ch {
-            '"' => in_quotes = !in_quotes,
+            '\\' if in_quotes => {
+                prev_backslash = !prev_backslash;
+                continue;
+            }
+            '"' if !prev_backslash => in_quotes = !in_quotes,
             ',' if !in_quotes => {
                 let token = header[start..i].trim();
                 if !token.is_empty() {
@@ -229,6 +234,7 @@ fn split_mailbox_list(header: &str) -> Vec<&str> {
             }
             _ => {}
         }
+        prev_backslash = false;
     }
 
     let token = header[start..].trim();
@@ -835,6 +841,30 @@ mod tests {
         assert!(addrs.is_empty());
     }
 
+    #[test]
+    fn test_split_mailbox_list_escaped_quotes() {
+        let addrs =
+            split_mailbox_list(r#""Doe \"JD, Sr\"" <john@example.com>, alice@example.com"#);
+        assert_eq!(
+            addrs,
+            vec![
+                r#""Doe \"JD, Sr\"" <john@example.com>"#,
+                "alice@example.com"
+            ]
+        );
+    }
+
+    #[test]
+    fn test_split_mailbox_list_double_backslash() {
+        // \\\\" inside quotes means an escaped backslash followed by a closing quote
+        let addrs =
+            split_mailbox_list(r#""Trail\\" <t@example.com>, b@example.com"#);
+        assert_eq!(
+            addrs,
+            vec![r#""Trail\\" <t@example.com>"#, "b@example.com"]
+        );
+    }
+
     #[test]
     fn test_reply_all_with_quoted_comma_display_name() {
         let original = OriginalMessage {