diff --git a/tests/test_request_diagnostics_cache.py b/tests/test_request_diagnostics_cache.py
index e4c0a1243..c18f08c8a 100644
--- a/tests/test_request_diagnostics_cache.py
+++ b/tests/test_request_diagnostics_cache.py
@@ -1,5 +1,4 @@
-from pathlib import Path
-
+import api.routes as routes
 from api.request_diagnostics import RequestDiagnostics
 
 
@@ -7,14 +6,84 @@ def test_request_diagnostics_maybe_start_still_covers_sessions_route():
     assert RequestDiagnostics.maybe_start("GET", "/api/sessions") is not None
 
 
-def test_sessions_route_emits_cache_diagnostic_stage_names():
-    src = Path("api/routes.py").read_text(encoding="utf-8")
+def _session_cache_diag_stage_names(diag: RequestDiagnostics) -> list[str]:
+    return [stage["name"] for stage in diag._stages] + [diag._current_stage]
 
-    for stage in (
+
+def _session_cache_key() -> tuple:
+    return routes._session_list_cache_key(
+        active_profile="default",
+        all_profiles=False,
+        show_cli_sessions=False,
+        show_previous_messaging_sessions=False,
+        show_cron_sessions=False,
+    )
+
+
+def test_sessions_route_emits_cache_hit_diagnostic_stages():
+    key = _session_cache_key()
+    routes._session_list_cache_clear()
+    routes._session_list_cache_set(key, {"sessions": [], "cli_count": 0})
+
+    diag = RequestDiagnostics("GET", "/api/sessions", auto_start=False)
+    payload = routes._get_cached_session_list_payload(
+        key=key,
+        builder=lambda: {"sessions": ["unexpected"]},
+        diag=diag,
+    )
+
+    assert payload == {"sessions": [], "cli_count": 0}
+    assert _session_cache_diag_stage_names(diag) == [
+        "start",
         "session_list_cache_lookup",
         "session_list_cache_hit",
-        "session_list_cache_wait",
+    ]
+
+
+def test_sessions_route_emits_cache_store_diagnostic_stages():
+    key = _session_cache_key()
+    routes._session_list_cache_clear()
+
+    diag = RequestDiagnostics("GET", "/api/sessions", auto_start=False)
+    payload = routes._get_cached_session_list_payload(
+        key=key,
+        builder=lambda: {"sessions": ["rebuilt"], "cli_count": 0},
+        diag=diag,
+    )
+
+    assert payload == {"sessions": ["rebuilt"], "cli_count": 0}
+    assert _session_cache_diag_stage_names(diag) == [
+        "start",
+        "session_list_cache_lookup",
+        "session_list_cache_rebuild_owner",
         "session_list_cache_stored",
+    ]
+
+
+def test_sessions_route_emits_invalidation_retry_diagnostic_stage():
+    key = _session_cache_key()
+    routes._session_list_cache_clear()
+    calls = {"count": 0}
+
+    def _builder():
+        calls["count"] += 1
+        if calls["count"] == 1:
+            routes._session_list_cache_clear()
+        return {"sessions": [calls["count"]], "cli_count": 0}
+
+    diag = RequestDiagnostics("GET", "/api/sessions", auto_start=False)
+    payload = routes._get_cached_session_list_payload(
+        key=key,
+        builder=_builder,
+        diag=diag,
+    )
+
+    assert payload == {"sessions": [2], "cli_count": 0}
+    assert calls["count"] == 2
+    assert _session_cache_diag_stage_names(diag) == [
+        "start",
+        "session_list_cache_lookup",
+        "session_list_cache_rebuild_owner",
         "session_list_cache_invalidated_during_rebuild",
-    ):
-        assert stage in src
+        "session_list_cache_stored",
+    ]