[Sanjays2402]

Description

PUT /v1/agent/force-leave/<node> answered 500 when the named node did not exist. Both the client and the server remove paths already detected this case and produced a "No node found" error, but nothing set it apart from a genuine server failure, so the HTTP layer fell back to 500.

This adds a small sentinel error in agent/consul for the not-found case, keeps the existing error text exactly as it was, and has the force-leave handler translate it into a 404 carrying the same message. The WAN path goes through the same handler, so it gets the same treatment.

Testing & Reproduction steps

Repro: start a single agent and run curl -X PUT <addr>/v1/agent/force-leave/nonexistent-node. Before this change the response was 500; after, it is 404 with agent: No node found with name 'nonexistent-node'.

Added TestAgent_ForceLeave_UnknownNode, which drives the handler the same way the existing force-leave tests do and expects a 404. The existing force-leave tests still pass: TestAgent_ForceLeave, TestAgent_ForceLeave_ACLDeny, TestAgent_ForceLeavePrune, and TestAgent_ForceLeavePrune_WAN.

Links

Fixes #21878

Note: the changelog entry follows as .changelog/<PR number>.txt in a follow-up commit on this branch, since the file has to be named after the PR number.

PR Checklist

• updated test coverage
• external facing docs updated (not needed, this only corrects the status code for an existing endpoint)
• appropriate backport labels added
• not a security concern

PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.

• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.

• If applicable, I've documented the impact of any changes to security controls.

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