Query the Jenkins build queue via REST and diagnose why items are pending or stuck

Documented steps

1. GET the whole queue as JSON: curl -u user:APITOKEN "JENKINS_URL/queue/api/json?pretty=true" - the queue serializes as an 'items' array.
2. Read each entry's why field for the human-readable pending reason (e.g. waiting for an executor, blocked by another build in progress).
3. Cross-check the blocked and stuck booleans alongside why: blocked means another build or required resource is in the way; stuck means the item has been starving for an executor for too long - stuck items are the ones worth alerting on.
4. Correlate an item to its job via its task field (for a normal job-backed item this is the job itself); verify the exact nested JSON shape against a live ?pretty=true response rather than assuming a schema, then match it to JENKINS_URL/job/<name>/api/json.
5. The item's id follows it from queue into the resulting build; causes[] and params add trigger cause and parameter context beyond why alone.
6. Cancel a pending item with POST JENKINS_URL/queue/cancelItem?id=<id>. Docs: https://www.jenkins.io/doc/book/using/remote-access-api/ and https://javadoc.jenkins.io/hudson/model/Queue.html