fix: normalize marker.match event tag to int to match the REST schema

The WS event carried the tag as str (verbatim from the MARK signal) when
present and as int when falling back to the registry, so one tag reached
consumers as two different values. Parse the signal's decimal (the exact
value we installed via 'mark <bpf> tag <id>') and keep the registered int
on malformed input; None only when neither side carries one.

tests/compute/marker/test_marker_manager.py

@@ -121,7 +121,11 @@ class TestMarkerListener:
         assert ev["node_id"] == "n1"
         assert ev["link_id"] == "l1"
         assert ev["filter"] == "f1"
-        assert ev["tag"] == "7"
+        # The event tag is normalized to int to match the REST schema — the
+        # signal echoes the decimal we installed, so str and int variants of
+        # the same tag must never reach consumers as different keys.
+        assert ev["tag"] == 7
+        assert isinstance(ev["tag"], int)
         assert ev["ts"] == pytest.approx(1700000000.123456)
         assert ev["len"] == 98
         # No dir= in the signal (legacy uBridge) → undirected.
@@ -163,6 +167,24 @@ class TestMarkerListener:
         lis.datagram_received(b"MARK 2.0 node=n filter=f tag=- len=20\n", None)
         assert fmgr.events[0][1]["tag"] == 42
 
+    def test_non_numeric_signal_tag_falls_back_to_registered(self):
+        # A corrupt/unknown signal value must not leak a str tag into the
+        # event stream — the registry's int wins.
+        fmgr = FakeMarkerManager()
+        fmgr.register("p", "n", "f", "l", tag=42)
+        lis = MarkerListener(fmgr)
+        lis.connection_made(None)
+        lis.datagram_received(b"MARK 2.0 node=n filter=f tag=oops len=20\n", None)
+        assert fmgr.events[0][1]["tag"] == 42
+
+    def test_no_tag_anywhere_is_none(self):
+        fmgr = FakeMarkerManager()
+        fmgr.register("p", "n", "f", "l", tag=None)
+        lis = MarkerListener(fmgr)
+        lis.connection_made(None)
+        lis.datagram_received(b"MARK 2.0 node=n filter=f tag=- len=20\n", None)
+        assert fmgr.events[0][1]["tag"] is None
+
     def test_link_in_signal_overrides_registry_link(self):
         # Per-link attribution (contract §3.2/§3.3): the signal's `link=` is
         # authoritative and must disambiguate links sharing a node+filter —