feat(ledger): quiet idle outbox polling

tests/application/test_slots_handler.py

@@ -207,6 +207,66 @@ def test_spy_true_no_watchdog_update():
     assert watchdog.last_seen(sid) is None  # still not updated (spy=True)
 
 
+def test_spy_response_exposes_ledger_outbox_metrics():
+    class _MetricsReader:
+        def metrics_snapshot(self):
+            return {
+                "available": True,
+                "scope": "process_lifetime",
+                "instance_key": "default",
+                "claims": {
+                    "empty_polls_total": 7,
+                    "claimed_batches_total": 1,
+                    "unavailable_total": 0,
+                    "lost_total": 0,
+                    "foreign_instance_total": 0,
+                },
+                "outcomes": {
+                    "completed_total": 1,
+                    "duplicate_completed_total": 0,
+                    "retryable_failure_total": 0,
+                    "conflict_blocked_total": 0,
+                    "permanent_failure_total": 0,
+                    "dead_lettered_total": 0,
+                },
+            }
+
+    repo, *_ = _wire()
+    handler = make_slots_rpc_handler(
+        repo,
+        ledger_outbox_metrics_reader=_MetricsReader(),
+    )
+
+    spy_payload = handler(_req(spy=True)).payload
+    strategy_payload = handler(_req(spy=False)).payload
+
+    assert spy_payload["ledger_outbox_metrics"]["claims"]["empty_polls_total"] == 7
+    assert "ledger_outbox_metrics" not in strategy_payload
+
+
+def test_spy_response_reports_metrics_unavailable_without_failing_slots():
+    class _FailingReader:
+        def metrics_snapshot(self):
+            raise RuntimeError("SECRET_METRICS_READER_FAILURE")
+
+    repo, *_ = _wire()
+    for reader in (None, _FailingReader()):
+        handler = make_slots_rpc_handler(
+            repo,
+            instance_key="default",
+            ledger_outbox_metrics_reader=reader,
+        )
+        payload = handler(_req(spy=True)).payload
+
+        assert len(payload["slots"]) == 2
+        assert payload["ledger_outbox_metrics"] == {
+            "available": False,
+            "scope": "process_lifetime",
+            "instance_key": "default",
+            "reason": "ledger_outbox_metrics_unavailable",
+        }
+
+
 # REQ-073 AC-4: spy=False (default) → holding watchdog updated
 def test_spy_false_updates_watchdog():
     repo, svc, _, _, watchdog, handler = _wire()