Route transaction aborts through logemit as 'aborted' events

The rollback warning is now a LogEvent (kind='aborted', WARNING level,
carrying the exception) dispatched via emit_event so logemit callbacks can
handle or restyle it. Default rendering: action in transaction color
without quotes, followed by ' transaction aborted: {exc}' in default
color.

tests/test_logemit.py

@@ -239,3 +239,30 @@ async def test_logmigr_failure_does_not_break_open(tmp_path, format_config):
     await kanta.open()
     assert kanta.data.counter == 2
     await kanta.close()
+
+
+@pytest.mark.asyncio
+async def test_aborted_transaction_emits_event(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+    events = []
+    kanta.logemit(lambda ev: events.append(ev) or True)
+    await kanta.open()
+
+    with caplog.at_level(logging.WARNING, logger="kanta.transaction"):
+        with pytest.raises(ValueError):
+            with kanta.transaction(action="reset") as data:
+                data.counter = 99
+                raise ValueError("simulated failure")
+
+    await kanta.close()
+
+    aborted = events[-1]
+    assert aborted.kind == "aborted"
+    assert aborted.action == "reset"
+    assert aborted.level == logging.WARNING
+    assert isinstance(aborted.error, ValueError)
+    messages = [r.getMessage() for r in caplog.records if r.levelno == logging.WARNING]
+    assert any("\x1b[1;34mreset" in m for m in messages)  # action color, no quotes
+    assert any(" transaction aborted: simulated failure" in m for m in messages)
+    assert kanta.data.counter == 0  # rolled back