Post a closure comment when the pre-created steering PR is discarded after a failed run

[Copilot]

When a failed workflow run closed its pre-created ("steering") pull request, no comment was added explaining the closure — even though the design intends to link back to the recorded agent-failure issue/comment when one exists.

Root cause

• failure_issue_number/failure_issue_url step outputs were only set when handle_agent_failure.cjs created a new failure issue, not when it added a comment to an existing one (the common case once an issue already exists for that failure signature).
• Because those outputs were empty, the conclusion step that closes the pre-created PR had nothing to link to and silently skipped commenting.
• There was also no fallback message at all for failed/cancelled runs that never produced a failure issue in the first place.

Changes

• handle_agent_failure.cjs: publish failure_issue_number/failure_issue_url outputs after commenting on an existing failure issue too, pointing at the specific comment (not just the issue) so downstream steps link directly to the relevant detail.
• complete_pre_created_check_run.cjs: restructured pre-created PR discard flow to always post an explanatory comment before closing on a failed/cancelled run:
  • a no-op message, if the run produced one (unchanged priority), otherwise
  • a message linking to the failure issue/comment, when available, otherwise
  • a generic message referencing the workflow run.
• Updated/extended unit tests in complete_pre_created_check_run.test.cjs to cover the new comment wording and the existing-issue linking path.

// Before: only set when a brand-new issue was created
setFailureIssueOutputs(newIssue.data);

// After: also set when commenting on an existing issue,
// pointing at the comment itself
setFailureIssueOutputs({ number: existingIssue.number, html_url: failureComment.html_url });