session-mode: availability must require the FALLBACK unit (plasma-mobile.service) as well as taos-kiosk.service, so a desk with no fallback is never offered a switch

changelog.d/tsk-mtf4dv-session-mode-needs-fallback.md

@@ -0,0 +1 @@
+### Fixed\n- Session mode availability now requires both taos-kiosk.service and plasma-mobile.service; desks without the fallback unit are not offered a switch.

tests/test_session_mode.py

@@ -92,3 +92,51 @@ async def json(self):
     resp = await system_routes.set_session_mode(_Req())
     assert resp.status_code == 400
     assert started == []
+
+
+@pytest.mark.asyncio
+async def test_state_unavailable_on_desk_without_fallback(monkeypatch):
+    async def fake(*args):
+        if args[0] == "cat":
+            unit = args[-1]
+            if unit == "taos-kiosk.service":
+                return 0, "# unit"
+            if unit == "plasma-mobile.service":
+                return 1, "No files found"
+            return 0, "# unit"
+        return 3, "inactive"
+
+    monkeypatch.setattr(system_routes, "_systemctl", fake)
+    state = await system_routes._session_mode_state()
+    assert state["available"] is False
+
+
+@pytest.mark.asyncio
+async def test_switch_refused_on_desk_without_fallback(monkeypatch):
+    started: list[str] = []
+
+    async def fake(*args):
+        if args[0] == "start":
+            started.append(args[-1])
+            return 0, ""
+        if args[0] == "cat":
+            unit = args[-1]
+            if unit == "taos-kiosk.service":
+                return 0, "# unit"
+            if unit == "plasma-mobile.service":
+                return 1, "No files found"
+            return 1, "No files found"
+        return 3, "inactive"
+
+    monkeypatch.setattr(system_routes, "_systemctl", fake)
+
+    class _Req:
+        async def body(self):
+            return b'{"mode":"kiosk"}'
+
+        async def json(self):
+            return {"mode": "kiosk"}
+
+    resp = await system_routes.set_session_mode(_Req())
+    assert resp.status_code == 404
+    assert started == []

tinyagentos/routes/system.py

@@ -358,7 +358,9 @@ async def _session_mode_state() -> dict:
     # and rc is not. An unknown unit reports "inactive" too, so availability is
     # probed separately with `cat`, which fails only when the unit is absent.
     cat_rc, _ = await _systemctl("cat", _SESSION_UNITS["kiosk"])
-    available = cat_rc == 0
+    # availability needs both units because a desk has the kiosk unit and no fallback
+    plasma_cat_rc, _ = await _systemctl("cat", _SESSION_UNITS["plasma"])
+    available = cat_rc == 0 and plasma_cat_rc == 0
     _, plasma_state = await _systemctl("is-active", _SESSION_UNITS["plasma"])
     if kiosk_state == "active":
         current = "kiosk"
@@ -397,7 +399,7 @@ async def set_session_mode(request: Request):
     state = await _session_mode_state()
     if not state["available"]:
         return JSONResponse(
-            {"error": "this device has no taOS kiosk session installed"}, status_code=404,
+            {"error": "this device has no second session to switch to"}, status_code=404,
         )
     # Starting the target stops the other: the units Conflict. Doing it as two
     # jobs (stop-then-start) would leave a window with NO session on screen.