Emit synthetic OTel exception events for failure conclusions without readable agent output

[Copilot]

✨ Enhancement

What does this improve?

Agent conclusion spans already marked failure as STATUS_CODE_ERROR, but when /tmp/gh-aw/agent_output.json was missing or unreadable they emitted no exception event. That left trace backends with a red span but no diagnosable failure signal to surface, group, or alert on.

Why is this valuable?

This keeps generic agent crashes aligned with the existing timed_out / cancelled synthetic-exception behavior, so failure traces remain queryable even when the agent never produces readable output.

• Conclusion span behavior

  • Extend the synthetic-exception path in send_otlp_span.cjs to cover all non-OK agent conclusions with unreadable output, including failure.
  • Emit:
    • exception.type = gh-aw.AgentFailed
    • exception.message = agent failure

• Failure-path coverage

  • Update the focused OTLP span tests to assert a synthetic exception event for:
    • missing agent_output.json
    • unreadable / invalid agent_output.json
  • Preserve the existing timeout and cancellation behavior unchanged.

• Example

  if (hasNoReadableAgentOutput && isAgentNonOK) {
    let exceptionType = "gh-aw.AgentFailed";
    if (isAgentTimedOut) exceptionType = "gh-aw.AgentTimedOut";
    else if (isAgentCancelled) exceptionType = "gh-aw.AgentCancelled";
  }

[Copilot]

Pull request overview

This PR improves OTLP conclusion-span observability by emitting a synthetic OpenTelemetry exception event when the agent concludes non-OK (including failure) but /tmp/gh-aw/agent_output.json is missing or unreadable, ensuring trace backends have a queryable failure signal even without agent output.

Changes:

• Extend synthetic-exception emission in sendJobConclusionSpan to trigger for any non-OK agent conclusion when there is no readable agent_output.json (adds gh-aw.AgentFailed for generic failures).
• Add/adjust focused tests to assert synthetic exception events for missing and unreadable agent_output.json on failure.

Show a summary per file

File	Description
actions/setup/js/send_otlp_span.cjs	Emit synthetic exception events for all non-OK conclusions when agent output is absent/unreadable (including failure).
actions/setup/js/send_otlp_span.test.cjs	Add assertions covering synthetic failure exceptions for missing/unreadable agent_output.json.

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