diff --git a/api/routes.py b/api/routes.py
index 18d9c1a5..ecd7912a 100644
--- a/api/routes.py
+++ b/api/routes.py
@@ -2629,9 +2629,13 @@ def handle_get(handler, parsed) -> bool:
     if parsed.path.startswith("/api/kanban/"):
         from api.kanban_bridge import handle_kanban_get
 
-        if handle_kanban_get(handler, parsed):
-            return True
-        return _kanban_unknown_endpoint(handler, parsed, "GET")
+        # Only treat an explicit False as "no route matched". None means the
+        # bridge already sent a response via bad()/j() — emitting our own 404
+        # on top of that produces concatenated JSON bodies on the wire.
+        result = handle_kanban_get(handler, parsed)
+        if result is False:
+            return _kanban_unknown_endpoint(handler, parsed, "GET")
+        return True
     if parsed.path == "/api/wiki/status":
         return _handle_llm_wiki_status(handler, parsed)
     if parsed.path == "/api/logs":
@@ -3429,9 +3433,10 @@ def handle_post(handler, parsed) -> bool:
     if parsed.path.startswith("/api/kanban/"):
         from api.kanban_bridge import handle_kanban_post
 
-        if handle_kanban_post(handler, parsed, body):
-            return True
-        return _kanban_unknown_endpoint(handler, parsed, "POST")
+        result = handle_kanban_post(handler, parsed, body)
+        if result is False:
+            return _kanban_unknown_endpoint(handler, parsed, "POST")
+        return True
     if parsed.path == "/api/dashboard/config":
         from api import dashboard_probe
 
@@ -4607,9 +4612,10 @@ def handle_patch(handler, parsed) -> bool:
     if parsed.path.startswith("/api/kanban/"):
         from api.kanban_bridge import handle_kanban_patch
 
-        if handle_kanban_patch(handler, parsed, body):
-            return True
-        return _kanban_unknown_endpoint(handler, parsed, "PATCH")
+        result = handle_kanban_patch(handler, parsed, body)
+        if result is False:
+            return _kanban_unknown_endpoint(handler, parsed, "PATCH")
+        return True
     return False
 
 
@@ -4621,9 +4627,10 @@ def handle_delete(handler, parsed) -> bool:
     if parsed.path.startswith("/api/kanban/"):
         from api.kanban_bridge import handle_kanban_delete
 
-        if handle_kanban_delete(handler, parsed, body):
-            return True
-        return _kanban_unknown_endpoint(handler, parsed, "DELETE")
+        result = handle_kanban_delete(handler, parsed, body)
+        if result is False:
+            return _kanban_unknown_endpoint(handler, parsed, "DELETE")
+        return True
     return False
 
 # ── GET route helpers ─────────────────────────────────────────────────────────
diff --git a/tests/test_issue1823_kanban_not_found.py b/tests/test_issue1823_kanban_not_found.py
index 6899994b..d9fdd3e2 100644
--- a/tests/test_issue1823_kanban_not_found.py
+++ b/tests/test_issue1823_kanban_not_found.py
@@ -67,6 +67,31 @@ def test_kanban_stale_client_error_renders_hard_refresh_escape_hatch():
     assert "window.location.reload()" in PANELS
 
 
+def test_inner_handler_bad_response_does_not_emit_double_404(monkeypatch):
+    """Regression: when the kanban bridge already sent a response via bad()
+    (returns None), the unknown-endpoint wrapper must not concatenate a second
+    404 body on the wire. Only an explicit `False` from the bridge means the
+    path was unmatched.
+    """
+    from api import kanban_bridge
+
+    # Force the task-log payload helper to report "not found" so the bridge
+    # calls bad() and returns None.
+    monkeypatch.setattr(kanban_bridge, "_task_log_payload", lambda *a, **kw: None)
+
+    handler = _FakeHandler()
+    handled = routes.handle_get(handler, urlparse("/api/kanban/tasks/abc/log"))
+
+    assert handled is True
+    assert handler.status == 404
+    body = handler.wfile.getvalue().decode("utf-8")
+    # Exactly one JSON object should have been written. Two concatenated
+    # objects would produce something like `}{` between them.
+    assert body.count("}{") == 0, f"double response detected: {body!r}"
+    payload = json.loads(body)
+    assert payload["error"] == "task not found"
+
+
 def test_kanban_load_resolves_board_before_board_scoped_requests():
     boards_pos = PANELS.find("await loadKanbanBoards();")
     config_pos = PANELS.find("api('/api/kanban/config' + _kanbanBoardQuery())")