[ZEPPELIN-1836] Make testAngularRunParagraph wait for rendered Angular output

[jongyoul]

What is this PR for?

testAngularRunParagraph has been failing on every frontend.yml test-selenium-with-spark-module-for-spark-3-5 run on master since the last green build at 6353224 on 2026-04-23. The failure is always at ZeppelinIT.java:348:

org.openqa.selenium.TimeoutException: Expected condition failed: waiting for visibility of element located by By.xpath: (//div[@ng-controller="ParagraphCtrl"])[1]//div[@id="angularRunParagraph"] (tried for 30 second(s) with 500 milliseconds interval)

Tracing the server log confirms the angular paragraph re-run completes successfully on the server side (paragraph FINISHED, result broadcast) and the stalenessOf(oldAngularDiv) check before visibilityWait does succeed — so the old angularRunParagraph div is detached as expected. The new div, however, is not detected as visible within 30s.

The race lives on the frontend side of the re-render: AngularJS' renderAngular() does elem.html(generated) and then $compile(elem.contents())(paragraphScope). Between those two calls the result div can be momentarily detached or empty, which is exactly the window visibilityWait polls into. Once it gets a stale reference, the wait does not refetch.

This builds on the stalenessOf + JavaScript-click fix from ZEPPELIN-6409 (#5209). That fix proved the old output was being torn down; this PR makes the wait for the new output equally tolerant of mid-$compile DOM churn.

What type of PR is it?

Bug Fix

Todos

• Replace single visibilityWait with a content-aware polling wait that re-finds the element and ignores StaleElementReferenceException
• Mirror the content-based pattern already used after the first run (waitForText(\"Run second paragraph\", ...))

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-1836 (long-standing flaky test ticket, open since 2016)

How should this be tested?

• CI frontend.yml → test-selenium-with-spark-module-for-spark-3-5 should run ZeppelinIT.testAngularRunParagraph to completion without timing out at line 348.
• Local repro (slow, requires -Pweb-classic and Spark 3.5):

  ./mvnw verify -DfailIfNoTests=false -pl zeppelin-integration \
    -Pweb-classic -Pintegration -Pspark-scala-2.12 -Pspark-3.5 -Pweb-dist -Pusing-source-tree \
    -Dit.test=ZeppelinIT#testAngularRunParagraph
  

Screenshots (if appropriate)

N/A

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No