test(e2e): assert backend dispatch matches workflow env vars on every lane

Adds a single smoke test at tests/src/e2e/basic/test_backend_dispatch_smoke.py
that runs on all three e2e lanes (testcontainer, HAOS external, HAOS inaddon)
and asserts ha_container_with_fresh_config["backend"] matches what the
HAOS_TEST_IMAGE_PATH and HAOS_TEST_MODE env vars imply.

Lane → expected backend:
  e2e-tests.yml (testcontainer):       container
  haos-e2e-tests.yml (external):       haos
  haos-e2e-inaddon-tests.yml:          haos_inaddon

Silent-failure modes this catches (would have left previous CI green):
- HAOS_TEST_IMAGE_PATH set but conftest falls through to testcontainer
  (the lane is unknowingly testing the wrong HA instance)
- HAOS_TEST_MODE=inaddon ignored, inaddon lane silently runs external
  dispatch — the addon integration is never actually exercised
- haos_inaddon backend reached but addon_mcp_url missing, leaving
  mcp_client fixtures pointing at the wrong endpoint

Placed under basic/ (NOT haos_only/) on purpose: the auto-applied
haos_only marker would skip the test when is_haos_backend_selected()
returns False, which is exactly the silent-failure case we want to
catch. basic/ has no auto-applied markers so the test runs everywhere.

Author: kingpanther13

tests/src/e2e/basic/test_backend_dispatch_smoke.py

@@ -0,0 +1,87 @@
+"""Verifies the conftest backend dispatch picks the backend CI asked for.
+
+The three e2e CI lanes set env vars that ``conftest.ha_container_with_fresh_config``
+reads to choose a backend:
+
+| Lane                          | HAOS_TEST_IMAGE_PATH | HAOS_TEST_MODE | expected backend |
+| ----------------------------- | -------------------- | -------------- | ---------------- |
+| e2e-tests.yml (testcontainer) | unset                | unset          | ``container``    |
+| haos-e2e-tests.yml (external) | set                  | unset          | ``haos``         |
+| haos-e2e-inaddon-tests.yml    | set                  | ``inaddon``    | ``haos_inaddon`` |
+
+Without an explicit assertion, the dispatch has silent-failure modes that
+all leave CI green while running tests against the wrong backend:
+
+1. ``HAOS_TEST_IMAGE_PATH`` set but ``is_haos_backend_selected()`` returns
+   False (env-var name drift, import-time bug) — both HAOS lanes silently
+   fall through to the testcontainer path.
+2. ``HAOS_TEST_MODE=inaddon`` set but ``is_haos_inaddon_mode()`` reads a
+   different name — inaddon lane silently runs the external dispatch,
+   so ``mcp_client`` talks to the in-process FastMCP server instead of
+   the addon's HTTP endpoint. The whole inaddon integration is untested.
+3. Inaddon dispatch reached but ``addon_mcp_url`` never populated —
+   downstream fixtures route to the wrong endpoint and surface as
+   confusing errors later.
+
+This file is placed under ``basic/`` (NOT ``haos_only/``) on purpose:
+the auto-applied ``haos_only`` marker in ``conftest.pytest_collection_modifyitems``
+would skip the test whenever ``is_haos_backend_selected()`` returns False,
+which is exactly the silent-failure case (1) above. We want the test to
+RUN on every lane and FAIL when the backend doesn't match the env.
+"""
+
+from __future__ import annotations
+
+import os
+from typing import Any
+
+
+def test_backend_dispatch_matches_workflow_env(
+    ha_container_with_fresh_config: dict[str, Any],
+) -> None:
+    """Conftest dispatch must pick the backend the workflow env implies.
+
+    Runs unconditionally on every lane — assertion branches off the env
+    vars to mirror conftest's own dispatch logic. Mismatch means the
+    dispatch silently picked a different backend than CI asked for.
+    """
+    image_path = os.environ.get("HAOS_TEST_IMAGE_PATH")
+    mode = os.environ.get("HAOS_TEST_MODE", "")
+    backend = ha_container_with_fresh_config["backend"]
+
+    if image_path and mode == "inaddon":
+        # haos-e2e-inaddon-tests.yml lane
+        assert backend == "haos_inaddon", (
+            f"Workflow set HAOS_TEST_IMAGE_PATH + HAOS_TEST_MODE=inaddon "
+            f"but dispatch picked backend={backend!r}. The inaddon "
+            f"integration is NOT being exercised by this run."
+        )
+        addon_mcp_url = ha_container_with_fresh_config.get("addon_mcp_url")
+        assert addon_mcp_url and addon_mcp_url.startswith("http"), (
+            f"haos_inaddon backend reported but addon_mcp_url is "
+            f"{addon_mcp_url!r}. mcp_client fixtures will route to the "
+            f"wrong endpoint."
+        )
+        assert ha_container_with_fresh_config["container"] is None
+    elif image_path:
+        # haos-e2e-tests.yml (external) lane
+        assert backend == "haos", (
+            f"Workflow set HAOS_TEST_IMAGE_PATH but dispatch picked "
+            f"backend={backend!r}. The lane silently fell through to "
+            f"the testcontainer path; tests are running against the "
+            f"wrong HA instance."
+        )
+        # External HAOS sets the testcontainer keys to None.
+        assert ha_container_with_fresh_config["container"] is None
+        assert ha_container_with_fresh_config["port"] is None
+        assert ha_container_with_fresh_config["config_path"] is None
+        # addon_mcp_url is the inaddon-only routing key.
+        assert ha_container_with_fresh_config["addon_mcp_url"] is None
+    else:
+        # e2e-tests.yml (testcontainer) lane
+        assert backend == "container", (
+            f"No HAOS env vars set, expected testcontainer backend, "
+            f"got backend={backend!r}."
+        )
+        assert ha_container_with_fresh_config["container"] is not None
+        assert ha_container_with_fresh_config["port"] is not None