diff --git a/tests/test_issue2066_stale_sidebar_spinner.py b/tests/test_issue2066_stale_sidebar_spinner.py
new file mode 100644
index 00000000..19e8f991
--- /dev/null
+++ b/tests/test_issue2066_stale_sidebar_spinner.py
@@ -0,0 +1,34 @@
+"""Regression checks for #2066 stale sidebar spinner state."""
+
+from pathlib import Path
+
+
+SESSIONS_JS = (Path(__file__).resolve().parent.parent / "static" / "sessions.js").read_text()
+
+
+def _function_block(name: str, next_name: str) -> str:
+    start = SESSIONS_JS.find(f"function {name}")
+    assert start != -1, f"{name} not found in sessions.js"
+    end = SESSIONS_JS.find(f"function {next_name}", start)
+    assert end != -1, f"{next_name} not found after {name}"
+    return SESSIONS_JS[start:end]
+
+
+def test_local_streaming_only_uses_active_session_busy_state():
+    block = _function_block("_isSessionLocallyStreaming", "_isSessionEffectivelyStreaming")
+
+    assert "const isActive = S.session && s.session_id === S.session.session_id;" in block
+    assert "return isActive && Boolean(S.busy);" in block
+    assert "INFLIGHT[s.session_id]" not in block
+    assert "INFLIGHT && INFLIGHT[s.session_id]" not in block
+
+
+def test_cache_render_purges_stale_non_streaming_inflight_entries():
+    purge_block = _function_block("_purgeStaleInflightEntries", "_rememberRenderedStreamingState")
+    render_block = _function_block("renderSessionListFromCache", "_showProjectPicker")
+
+    assert "const s = _allSessionsById.get(sid);" in purge_block
+    assert "if (s && !s.is_streaming)" in purge_block
+    assert "delete INFLIGHT[sid];" in purge_block
+    assert "clearInflightState(sid);" in purge_block
+    assert "_purgeStaleInflightEntries();" in render_block
diff --git a/tests/test_issue856_background_completion_unread.py b/tests/test_issue856_background_completion_unread.py
index 47a7da6c..324a535e 100644
--- a/tests/test_issue856_background_completion_unread.py
+++ b/tests/test_issue856_background_completion_unread.py
@@ -186,8 +186,8 @@ def test_polling_transition_tracks_the_same_effective_streaming_state_as_sidebar
     assert render_idx != -1, "_renderOneSession not found"
     render_block = SESSIONS_JS[render_idx:SESSIONS_JS.find("const hasUnread=", render_idx)]
 
-    assert "(isActive && S.busy)" in local_block
-    assert "INFLIGHT && INFLIGHT[s.session_id]" in local_block
+    assert "isActive && Boolean(S.busy)" in local_block
+    assert "INFLIGHT && INFLIGHT[s.session_id]" not in local_block
     assert "s.is_streaming || _isSessionLocallyStreaming(s)" in effective_block
     assert "const isStreaming=_isSessionEffectivelyStreaming(s);" in render_block, (
         "the row spinner and polling completion transition must use the same "
diff --git a/tests/test_issue856_pinned_indicator_layout.py b/tests/test_issue856_pinned_indicator_layout.py
index 31a30778..93b2d644 100644
--- a/tests/test_issue856_pinned_indicator_layout.py
+++ b/tests/test_issue856_pinned_indicator_layout.py
@@ -129,8 +129,9 @@ def test_sidebar_uses_local_inflight_state_for_immediate_spinner():
     messages_js = (Path(__file__).resolve().parent.parent / "static" / "messages.js").read_text()
 
     assert "function _isSessionLocallyStreaming(s)" in SESSIONS_JS
-    assert "(isActive && S.busy)" in SESSIONS_JS
-    assert "INFLIGHT[s.session_id]" in SESSIONS_JS
+    assert "isActive && Boolean(S.busy)" in SESSIONS_JS
+    assert "function _purgeStaleInflightEntries()" in SESSIONS_JS
+    assert "delete INFLIGHT[sid];" in SESSIONS_JS
     assert "function _isSessionEffectivelyStreaming(s)" in SESSIONS_JS
     assert "const isStreaming=_isSessionEffectivelyStreaming(s);" in SESSIONS_JS
     assert "if(typeof renderSessionListFromCache==='function') renderSessionListFromCache();" in messages_js