feat: validate Selected PR: none in cleanup mode when queue is empty

pr_queue_cleanup.py

@@ -132,6 +132,13 @@ def check_cleanup_task_allowed(task: str) -> tuple[bool, list[str]]:
 _SELECTED_PR_RE = re.compile(
     r"^\s*[-*]?\s*selected pr\s*:\s*#?(\d+)", re.IGNORECASE | re.MULTILINE
 )
+_SELECTED_PR_NONE_RE = re.compile(
+    r"^\s*[-*]?\s*selected pr\s*:\s*(?:none|n/a)\b", re.IGNORECASE | re.MULTILINE
+)
+_EMPTY_QUEUE_RE = re.compile(
+    r"\b0 open pr|\bno open pr|\bno eligible pr|\bempty (?:review )?queue|\binventory empty|\btrusted_empty\b",
+    re.IGNORECASE,
+)
 _NEXT_SUGGESTED_RE = re.compile(
     r"^\s*[-*]?\s*next suggested pr\s*:", re.IGNORECASE | re.MULTILINE
 )
@@ -176,7 +183,11 @@ def assess_pr_queue_cleanup_report(report_text: str) -> dict:
 
     selected = _SELECTED_PR_RE.findall(text)
     if len(selected) == 0:
-        reasons.append("report must name exactly one Selected PR")
+        if _SELECTED_PR_NONE_RE.search(text):
+            if not _EMPTY_QUEUE_RE.search(text):
+                reasons.append("Selected PR is 'none' but no valid empty-queue claim found")
+        else:
+            reasons.append("report must name exactly one Selected PR")
     elif len(set(selected)) > 1:
         reasons.append(
             "cleanup run selected multiple PRs "
@@ -184,6 +195,9 @@ def assess_pr_queue_cleanup_report(report_text: str) -> dict:
             "PR per run"
         )
 
+    if len(selected) > 0 and _SELECTED_PR_NONE_RE.search(text):
+        reasons.append("report contains both a selected PR and a claim of none selected")
+
     terminal = _TERMINAL_MUTATION_RE.findall(text)
     if len(terminal) > 1:
         reasons.append(