diff --git a/inire/geometry/components.py b/inire/geometry/components.py
index 0808694..0d61862 100644
--- a/inire/geometry/components.py
+++ b/inire/geometry/components.py
@@ -49,7 +49,7 @@ class ComponentResult:
             _offsets: list[int] | None = None,
             _coords_cache: numpy.ndarray | None = None,
             _base_result: ComponentResult | None = None,
-            _offset: list[float] | None = None,
+            _offset: numpy.ndarray | None = None,
             snap_size: float = SEARCH_GRID_SNAP_UM,
             rel_gx: int | None = None,
             rel_gy: int | None = None,
@@ -216,17 +216,18 @@ class ComponentResult:
         base = self._base_result
         if base is not None:
              dx, dy = self._offset
+             shift = numpy.array([dx, dy, dx, dy])
              # Vectorized addition is faster if we avoid creating new lists/arrays in the loop
              if base._bounds is not None:
-                  self._bounds = base._bounds + [dx, dy, dx, dy]
+                  self._bounds = base._bounds + shift
              if base._total_bounds is not None:
                   b = base._total_bounds
-                  self._total_bounds = numpy.array([b[0]+dx, b[1]+dy, b[2]+dx, b[3]+dy])
+                  self._total_bounds = b + shift
              if base._dilated_bounds is not None:
-                  self._dilated_bounds = base._dilated_bounds + [dx, dy, dx, dy]
+                  self._dilated_bounds = base._dilated_bounds + shift
              if base._total_dilated_bounds is not None:
                   b = base._total_dilated_bounds
-                  self._total_dilated_bounds = numpy.array([b[0]+dx, b[1]+dy, b[2]+dx, b[3]+dy])
+                  self._total_dilated_bounds = b + shift
         self._bounds_cached = True
 
     def translate(self, dx: float, dy: float, rel_gx: int | None = None, rel_gy: int | None = None, rel_go: int | None = None) -> ComponentResult:
@@ -241,10 +242,10 @@ class ComponentResult:
         if self._base_result:
              base = self._base_result
              current_offset = self._offset
-             new_offset = [current_offset[0] + dx, current_offset[1] + dy]
+             new_offset = numpy.array([current_offset[0] + dx, current_offset[1] + dy])
         else:
              base = self
-             new_offset = [dx, dy]
+             new_offset = numpy.array([dx, dy])
 
         return ComponentResult(
             end_port=new_port,
@@ -607,6 +608,11 @@ class SBend:
              
         actual_radius = abs(local_dy) / denom
         
+        # Safety Check: Reject SBends with tiny radii that would cause self-overlap
+        # (inner_radius becomes negative if actual_radius < width/2)
+        if actual_radius < width:
+             raise ValueError(f"SBend actual_radius {actual_radius:.3f} is too small (width={width})")
+
         # Limit radius to prevent giant arcs
         if actual_radius > 100000.0:
              actual_len = numpy.sqrt(local_dx**2 + local_dy**2)
diff --git a/inire/router/astar.py b/inire/router/astar.py
index abc0e84..7f874b3 100644
--- a/inire/router/astar.py
+++ b/inire/router/astar.py
@@ -56,7 +56,8 @@ class AStarRouter:
     """
     __slots__ = ('cost_evaluator', 'config', 'node_limit', 'visibility_manager', 
                  '_hard_collision_set', '_congestion_cache', '_static_safe_cache', 
-                 '_move_cache', 'total_nodes_expanded', 'last_expanded_nodes', 'metrics')
+                 '_move_cache', 'total_nodes_expanded', 'last_expanded_nodes', 'metrics',
+                 '_self_collision_check')
 
     def __init__(self, cost_evaluator: CostEvaluator, node_limit: int | None = None, **kwargs) -> None:
         self.cost_evaluator = cost_evaluator
@@ -121,11 +122,25 @@ class AStarRouter:
             return_partial: bool = False,
             store_expanded: bool = False,
             skip_congestion: bool = False,
-            max_cost: float | None = None
+            max_cost: float | None = None,
+            self_collision_check: bool = False,
             ) -> list[ComponentResult] | None:
         """
         Route a single net using A*.
+
+        Args:
+            start: Starting port.
+            target: Target port.
+            net_width: Waveguide width.
+            net_id: Identifier for the net.
+            bend_collision_type: Type of collision model to use for bends.
+            return_partial: If True, returns the best-effort path if target not reached.
+            store_expanded: If True, keep track of all expanded nodes for visualization.
+            skip_congestion: If True, ignore other nets' paths (greedy mode).
+            max_cost: Hard limit on f_cost to prune search.
+            self_collision_check: If True, prevent the net from crossing its own path.
         """
+        self._self_collision_check = self_collision_check
         self._congestion_cache.clear()
         if store_expanded:
             self.last_expanded_nodes = []
@@ -440,6 +455,22 @@ class AStarRouter:
                 total_overlaps = self.cost_evaluator.collision_engine.check_move_congestion(result, net_id)
                 self._congestion_cache[cache_key] = total_overlaps
 
+        # SELF-COLLISION CHECK (Optional for performance)
+        if getattr(self, '_self_collision_check', False):
+            curr_p = parent
+            new_tb = result.total_bounds
+            while curr_p and curr_p.parent:
+                 ancestor_res = curr_p.component_result
+                 if ancestor_res:
+                      anc_tb = ancestor_res.total_bounds
+                      if (new_tb[0] < anc_tb[2] and new_tb[2] > anc_tb[0] and
+                          new_tb[1] < anc_tb[3] and new_tb[3] > anc_tb[1]):
+                           for p_anc in ancestor_res.geometry:
+                                for p_new in result.geometry:
+                                     if p_new.intersects(p_anc) and not p_new.touches(p_anc):
+                                          return
+                 curr_p = curr_p.parent
+
         penalty = 0.0
         if 'SB' in move_type: penalty = self.config.sbend_penalty
         elif 'B' in move_type: penalty = self.config.bend_penalty
diff --git a/inire/router/pathfinder.py b/inire/router/pathfinder.py
index 193853c..55e4b14 100644
--- a/inire/router/pathfinder.py
+++ b/inire/router/pathfinder.py
@@ -144,6 +144,31 @@ class PathFinder:
         logger.info(f"PathFinder: Greedy Warm-Start finished. Seeding {len(greedy_paths)}/{len(netlist)} nets.")
         return greedy_paths
 
+    def _has_self_collision(self, path: list[ComponentResult]) -> bool:
+        """
+        Quickly check if a path intersects itself.
+        """
+        if not path:
+            return False
+            
+        num_components = len(path)
+        for i in range(num_components):
+            comp_i = path[i]
+            tb_i = comp_i.total_bounds
+            for j in range(i + 2, num_components): # Skip immediate neighbors
+                comp_j = path[j]
+                tb_j = comp_j.total_bounds
+                
+                # AABB Check
+                if (tb_i[0] < tb_j[2] and tb_i[2] > tb_j[0] and
+                    tb_i[1] < tb_j[3] and tb_i[3] > tb_j[1]):
+                    # Real geometry check
+                    for p_i in comp_i.geometry:
+                        for p_j in comp_j.geometry:
+                            if p_i.intersects(p_j) and not p_i.touches(p_j):
+                                return True
+        return False
+
     def route_all(
             self,
             netlist: dict[str, tuple[Port, Port]],
@@ -180,6 +205,7 @@ class PathFinder:
         session_timeout = max(60.0, 10.0 * num_nets * self.max_iterations)
 
         all_net_ids = list(netlist.keys())
+        needs_sc = set()  # Nets requiring self-collision avoidance
         
         # Determine initial paths (Warm Start)
         if initial_paths is None:
@@ -249,7 +275,7 @@ class PathFinder:
                     original_limit = self.router.node_limit
                     self.router.node_limit = current_node_limit
                     
-                    path = self.router.route(start, target, width, net_id=net_id, bend_collision_type=coll_model, return_partial=True, store_expanded=store_expanded, skip_congestion=skip_cong)
+                    path = self.router.route(start, target, width, net_id=net_id, bend_collision_type=coll_model, return_partial=True, store_expanded=store_expanded, skip_congestion=skip_cong, self_collision_check=(net_id in needs_sc))
                     
                     if store_expanded and self.router.last_expanded_nodes:
                         self.accumulated_expanded_nodes.extend(self.router.last_expanded_nodes)
@@ -258,6 +284,13 @@ class PathFinder:
                     logger.debug(f'  Net {net_id} routed in {time.monotonic() - net_start:.4f}s using {coll_model}')
 
                 if path:
+                    # Check for self-collision if not already handled by router
+                    if net_id not in needs_sc:
+                         if self._has_self_collision(path):
+                              logger.info(f'  Net {net_id} detected self-collision. Enabling protection for next iteration.')
+                              needs_sc.add(net_id)
+                              any_congestion = True
+
                     # Check if reached exactly
                     last_p = path[-1].end_port
                     reached = (abs(last_p.x - target.x) < 1e-6 and
diff --git a/inire/tests/test_failed_net_congestion.py b/inire/tests/test_failed_net_congestion.py
new file mode 100644
index 0000000..cc40951
--- /dev/null
+++ b/inire/tests/test_failed_net_congestion.py
@@ -0,0 +1,74 @@
+
+import pytest
+import numpy
+from inire.geometry.primitives import Port
+from inire.geometry.collision import CollisionEngine
+from inire.router.cost import CostEvaluator
+from inire.router.astar import AStarRouter
+from inire.router.pathfinder import PathFinder
+from inire.router.danger_map import DangerMap
+
+def test_failed_net_visibility():
+    """
+    Verifies that nets that fail to reach their target (return partial paths)
+    ARE added to the collision engine, making them visible to other nets
+    for negotiated congestion.
+    """
+    # 1. Setup
+    engine = CollisionEngine(clearance=2.0)
+    
+    # Create a simple danger map (bounds 0-100)
+    # We don't strictly need obstacles in it for this test.
+    dm = DangerMap(bounds=(0, 0, 100, 100))
+    
+    evaluator = CostEvaluator(engine, dm)
+    
+    # 2. Configure Router with low limit to FORCE failure
+    # node_limit=5 is extremely low, likely allowing only a few moves.
+    # Start (0,0) -> Target (100,0) is 100um away.
+    # If snap is 1.0, direct jump S100 might be tried.
+    # If direct jump works, it might succeed in 1 expansion.
+    # So we need to block the direct jump or make the limit VERY small (0?).
+    # Or place a static obstacle that forces a search.
+    
+    # Let's add a static obstacle that blocks the direct path.
+    from shapely.geometry import box
+    obstacle = box(40, -10, 60, 10) # Wall at x=50
+    engine.add_static_obstacle(obstacle)
+    
+    # With obstacle, direct jump fails. A* must search around.
+    # Limit=10 should be enough to fail to find a path around.
+    router = AStarRouter(evaluator, node_limit=10)
+    
+    # 3. Configure PathFinder
+    # max_iterations=1 because we only need to check the state after the first attempt.
+    pf = PathFinder(router, evaluator, max_iterations=1, warm_start=None)
+    
+    netlist = {
+        "net1": (Port(0, 0, 0), Port(100, 0, 0))
+    }
+    net_widths = {"net1": 1.0}
+    
+    # 4. Route
+    print("\nStarting Route...")
+    results = pf.route_all(netlist, net_widths)
+    
+    res = results["net1"]
+    print(f"Result: is_valid={res.is_valid}, reached={res.reached_target}, path_len={len(res.path)}")
+    
+    # 5. Verify Failure Condition
+    # We expect reached_target to be False because of node_limit + obstacle
+    assert not res.reached_target, "Test setup failed: Net reached target despite low limit!"
+    assert len(res.path) > 0, "Test setup failed: No partial path returned!"
+    
+    # 6. Verify Visibility
+    # Check if net1 is in the collision engine
+    found_nets = set()
+    # CollisionEngine.dynamic_geometries: dict[obj_id, (net_id, poly)]
+    for obj_id, (nid, poly) in engine.dynamic_geometries.items():
+        found_nets.add(nid)
+        
+    print(f"Nets found in engine: {found_nets}")
+    
+    # The FIX Expectation: "net1" SHOULD be present
+    assert "net1" in found_nets, "Bug present: Net1 is invisible despite having partial path!"