An element operation failure with its backend's original cause.
backend is :phoenix or :playwright; driver identifies the active driver.
operation names the public action and locator is the query or captured
file-chooser key. cause retains a native Playwright error or a structured
Phoenix Fluffy.StrictnessError or Fluffy.ActionabilityError.
No shared fine-grained failure category is inferred for browser errors.
Failed assertions remain ExUnit.AssertionError. Invalid arguments,
unsupported capabilities, and unexpected programming errors are not wrapped.