fix: idle detection + exponential backoff for dev loop (#435)

Co-authored-by: Kimi Agent <kimi@timmy.local>
Co-committed-by: Kimi Agent <kimi@timmy.local>

scripts/cycle_retro.py

@@ -149,6 +149,11 @@ def update_summary() -> None:
 def main() -> None:
     args = parse_args()
 
+    # Reject idle cycles — no issue and no duration means nothing happened
+    if not args.issue and args.duration == 0:
+        print(f"[retro] Cycle {args.cycle} skipped — idle (no issue, no duration)")
+        return
+
     # A cycle is only truly successful if hermes exited clean AND main is green
     truly_success = args.success and args.main_green