Scheduling pre-step: sys.exit(1) fails workflow noisily when no programs are due

[mrjf]

Problem

When no programs are due for a scheduled run, the scheduling pre-step exits with sys.exit(1) (line 456 of .github/workflows/autoloop.md):

if not selected and not unconfigured:
    print("\nNo programs due this run. Exiting early.")
    sys.exit(1)  # Non-zero exit skips the agent step

This causes the workflow run to show as failed (red X) in the Actions UI, even though "no programs due" is a normal, expected outcome for scheduled runs. On a 6-hour schedule, most runs will have nothing to do — each one creates a noisy failure notification.

Proposed fix

Exit successfully and gate the agent step on an output flag instead:

1. Write a sentinel to /tmp/gh-aw/autoloop.json indicating no programs are selected (similar to the existing no_programs case on line 268-269 which already uses sys.exit(0)).
2. Have the agent step check the sentinel and skip itself when there's nothing to run.

This keeps "no programs due" as a quiet success while still preventing the agent from running unnecessarily.

Origin

Flagged by Copilot code review on github/gh-aw#24345.

File to change

.github/workflows/autoloop.md — scheduling pre-step, currently line ~456.