add loop detection configuration and tests for flood routing

tests/test_engine.py

@@ -46,6 +46,7 @@ def _make_config(**overrides) -> dict:
         },
         "mesh": {
             "global_flood_allow": True,
+            "loop_detect": "off",
         },
         "delays": {
             "tx_delay_factor": 1.0,
@@ -679,6 +680,46 @@ class TestGlobalFloodPolicy:
         assert result is None
 
 
+class TestFloodLoopDetection:
+    """MeshCore-style loop detection for flood forwarding."""
+
+    def test_loop_detect_off_allows_looped_path(self, handler):
+        handler.config["mesh"]["loop_detect"] = "off"
+        handler.reload_runtime_config()
+        pkt = _make_flood_packet(path=bytes([LOCAL_HASH, 0x11, LOCAL_HASH]))
+        result = handler.flood_forward(pkt)
+        assert result is not None
+
+    def test_loop_detect_minimal_drops_at_four(self, handler):
+        handler.config["mesh"]["loop_detect"] = "minimal"
+        handler.reload_runtime_config()
+        pkt = _make_flood_packet(path=bytes([LOCAL_HASH, LOCAL_HASH, LOCAL_HASH, LOCAL_HASH]))
+        result = handler.flood_forward(pkt)
+        assert result is None
+        assert "loop detected" in (pkt.drop_reason or "").lower()
+
+    def test_loop_detect_minimal_allows_below_threshold(self, handler):
+        handler.config["mesh"]["loop_detect"] = "minimal"
+        handler.reload_runtime_config()
+        pkt = _make_flood_packet(path=bytes([LOCAL_HASH, LOCAL_HASH, LOCAL_HASH]))
+        result = handler.flood_forward(pkt)
+        assert result is not None
+
+    def test_loop_detect_moderate_drops_at_two(self, handler):
+        handler.config["mesh"]["loop_detect"] = "moderate"
+        handler.reload_runtime_config()
+        pkt = _make_flood_packet(path=bytes([LOCAL_HASH, 0x22, LOCAL_HASH]))
+        result = handler.flood_forward(pkt)
+        assert result is None
+
+    def test_loop_detect_strict_drops_at_one(self, handler):
+        handler.config["mesh"]["loop_detect"] = "strict"
+        handler.reload_runtime_config()
+        pkt = _make_flood_packet(path=bytes([0x33, LOCAL_HASH, 0x44]))
+        result = handler.flood_forward(pkt)
+        assert result is None
+
+
 # ===================================================================
 # 10. Airtime / duty-cycle integration
 # ===================================================================