The architecture of Ente (https://ente.io/architecture) prevents your unencrypted master key from being exposed to the server. The password authentication appears to be client-side, which means that the data could not be compromised solely by a malicious server-side change.
Now, Ente could still change its web application to somehow leak the master key and not disclose the changes in the source repo. One solution for this vulnerability is to package the entire web client as a browser extension, which is what Mega is doing:
There are a couple of other ways to mitigate the problem for web applications. If you're willing to install a browser extension, then it might make more sense to use the Signed Pages extension[0] which applies PGP signature checking to web pages. The other solution is to use Secure Bookmarks[1], which combine SRI integrity hashes with Data URIs to ensure that a fixed bundle of JavaScript is running in the page.
Now, Ente could still change its web application to somehow leak the master key and not disclose the changes in the source repo. One solution for this vulnerability is to package the entire web client as a browser extension, which is what Mega is doing:
https://github.com/meganz/web-extension