Assert on a price inside a shadow root

The Practice Hub renders prices through a custom element:

html

<shadow-price value="129.99"></shadow-price>

Its shadow root contains:

html

#shadow-root (open)
  <span class="price">$129.99</span>

Your colleague's Selenium test fails with NoSuchElementException:

java

String price = driver.findElement(By.cssSelector("span.price")).getText();
assertEquals("$129.99", price);

Your task: explain why it fails, then show how to read that price in Selenium, Playwright and Cypress. Finish with the assertion you would actually write and why it differs from the one above.