fix(openapi): use exact-match dedup in default_operation_id_creator

`default_operation_id_creator` builds an operationId by concatenating
title-cased path components, skipping a component if it's already
present via `component.title() not in components_namespace` — a
substring check against the concatenated string, not an exact-match
check against individual components.

This causes false collisions: for path components `["users", "user"]`,
"User" is a substring of the already-accumulated "Users", so the
"user" component is silently dropped, producing the same operationId
("UsersGetHandler") as a route whose only component is `["users"]`.
Two structurally different routes can end up with identical
operationIds, which OpenAPI requires to be unique
(test_routes_with_different_paths_should_generate_unique_operation_ids
already encodes this invariant, just not for this substring case).

Fix: track seen component titles in a set and check membership there
instead of doing a substring check against the concatenated namespace
string. This preserves the original intent (skip an exact-duplicate
component, e.g. when a router prefix repeats a literal path segment)
without falsely dropping components that merely share a substring.

How verified: reproduced the collision directly against
default_operation_id_creator with ["users"] vs ["users", "user"])
producing the same id; added a regression test
(test_default_operation_id_creator_does_not_collide_on_component_substring)
confirmed failing before the fix (AssertionError: 'UsersGetHandler' !=
'UsersGetHandler'); applied the fix; confirmed all 23 tests in
test_path_item.py and the full 262-test tests/unit/test_openapi/ suite
pass. mypy clean, pre-commit clean (ruff, unasyncd, typos).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: chuenchen309

litestar/_openapi/utils.py

@@ -39,8 +39,11 @@ def default_operation_id_creator(
     )
 
     components_namespace = ""
+    seen_components: set[str] = set()
     for component in (c.name if isinstance(c, PathParameterDefinition) else c for c in path_components):
-        if component.title() not in components_namespace:
-            components_namespace += component.title()
+        title = component.title()
+        if title not in seen_components:
+            seen_components.add(title)
+            components_namespace += title
 
     return SEPARATORS_CLEANUP_PATTERN.sub("", components_namespace + handler_namespace)

tests/unit/test_openapi/test_path_item.py

@@ -129,6 +129,20 @@ def test_routes_with_different_paths_should_generate_unique_operation_ids(
     assert schema_v1.get.operation_id != schema_v2.get.operation_id
 
 
+def test_default_operation_id_creator_does_not_collide_on_component_substring() -> None:
+    handler = MagicMock()
+    handler.handler_name = "get_handler"
+    handler.http_methods = ["GET"]
+
+    # "user" is a substring of the already-accumulated "Users", but it is a distinct,
+    # additional path component and must not be dropped from the generated id.
+    id_for_users = default_operation_id_creator(handler, "GET", ["users"])
+    id_for_users_user = default_operation_id_creator(handler, "GET", ["users", "user"])
+
+    assert id_for_users != id_for_users_user
+    assert id_for_users_user == "UsersUserGetHandler"
+
+
 def test_create_path_item_use_handler_docstring_false(
     http_route: HTTPRoute, create_factory: CreateFactoryFixture
 ) -> None: