fix: isolate ledger outbox delivery by instance

Co-authored-by: genichin <4282227+genichin@users.noreply.github.com>

tests/application/test_ledger_outbox.py

@@ -83,3 +83,30 @@ def test_process_correlation_id_only_drains_requested_row():
     assert ledger.count() == 1
     assert outbox.get(first.correlation_id).status is WorkItemStatus.COMPLETED
     assert outbox.get(second.correlation_id).status is WorkItemStatus.PENDING
+
+
+def test_process_correlation_id_skips_foreign_instance_row():
+    outbox = InMemoryLedgerOutbox(instance_key="inst-a")
+    ledger = InMemoryLedger()
+    writer = LedgerWriter(outbox, ledger, instance_key="inst-b")
+    item = outbox.enqueue(_trade(execution_id="e-foreign"))
+
+    outcome = writer.process_correlation_id(item.correlation_id)
+
+    assert outcome is None
+    assert ledger.count() == 0
+    assert writer.counters["claim:foreign_instance"] == 1
+    assert outbox.get(item.correlation_id).status is WorkItemStatus.PENDING
+
+
+def test_writer_exposes_claim_and_outcome_counters():
+    outbox = InMemoryLedgerOutbox(instance_key="inst-a")
+    ledger = InMemoryLedger()
+    writer = LedgerWriter(outbox, ledger, instance_key="inst-a")
+    outbox.enqueue(_trade(execution_id="e-count"))
+
+    stats = writer.run_once()
+
+    assert stats.completed == 1
+    assert writer.counters["claim:claimed"] == 1
+    assert writer.counters["outcome:completed"] == 1