fix(02-03): expand expected placeholders after replay capture

Unquoted numeric id placeholders made recorded JSON illegal to parse.
Replay now recaptures, persists vars, expands the expected body, and
diffs against the live response.

Co-authored-by: Cursor <cursoragent@cursor.com>

tide/variables.go

@@ -199,6 +199,26 @@ func expandRequest(req Request, store *Store) (Request, error) {
 	return out, nil
 }
 
+func expandResponse(resp Response, store *Store) (Response, error) {
+	out := resp
+	var err error
+	if resp.Headers != nil {
+		out.Headers = make(map[string]string, len(resp.Headers))
+		for k, v := range resp.Headers {
+			out.Headers[k], err = store.Expand(v)
+			if err != nil {
+				return Response{}, err
+			}
+		}
+	}
+	body, err := store.Expand(string(resp.Body))
+	if err != nil {
+		return Response{}, err
+	}
+	out.Body = Body(body)
+	return out, nil
+}
+
 // CaptureStep writes named values from the step into the store.
 func CaptureStep(store *Store, step *Step) error {
 	if store == nil || step == nil || len(step.Capture) == 0 {