fix(proxy): parse SSE fields with optional spaces in streaming handlers (#1664)

* fix(proxy): handle SSE fields with or without spaces

* refactor(proxy): deduplicate SSE field parsing

src-tauri/src/proxy/sse.rs

@@ -0,0 +1,31 @@
+#[inline]
+pub(crate) fn strip_sse_field<'a>(line: &'a str, field: &str) -> Option<&'a str> {
+    line.strip_prefix(&format!("{field}: "))
+        .or_else(|| line.strip_prefix(&format!("{field}:")))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::strip_sse_field;
+
+    #[test]
+    fn strip_sse_field_accepts_optional_space() {
+        assert_eq!(
+            strip_sse_field("data: {\"ok\":true}", "data"),
+            Some("{\"ok\":true}")
+        );
+        assert_eq!(
+            strip_sse_field("data:{\"ok\":true}", "data"),
+            Some("{\"ok\":true}")
+        );
+        assert_eq!(
+            strip_sse_field("event: message_start", "event"),
+            Some("message_start")
+        );
+        assert_eq!(
+            strip_sse_field("event:message_start", "event"),
+            Some("message_start")
+        );
+        assert_eq!(strip_sse_field("id:1", "data"), None);
+    }
+}