WorkflowRunner: force-released agent treated as successful step completion

[jahala]

Problem

When an agent is force-released after idle nudging, the runner treats the step as successfully completed with a stub output string.

runner.js ~L2104-2108:

exitResult === 'released'
 ? 'Agent completed (force-released after idle nudging)'
 : `Agent exited (${exitResult})`

This string becomes the step's output. Downstream steps that depend on {{steps.X.output}} receive "Agent completed (force-released after idle nudging)" as input — which is garbage.

The step is marked completed, not failed, so the retry loop is never triggered.

Suggestion

Force-release should throw an error in the step execution path, triggering the existing retry loop:

if (exitResult === 'released') {
 throw new Error('Agent force-released after idle timeout — step did not complete');
}

If retries are available, the step retries (ideally with the failure context from issue #497). If retries are exhausted, the step fails with a clear error. Downstream steps are skipped per the error handling strategy — not fed garbage.

Location: spawnAndWait in runner.js, where exitResult is handled after the idle nudging loop.