test: widen fixed-window assertions after busy-reset reorder

The #5917 reorder (idle busy/stream reset moved before the visit-ack) shifted
code positions, so two pre-existing fixed-offset source-assertion tests
truncated: extend gateway_sse_reconnect_dedupe's loadSession _block end-anchor to
_mergePendingSessionMessage, and widen stale_stream_cleanup's 900->1400 char
window past the expanded comment. Behavior unchanged.

tests/test_gateway_sse_reconnect_dedupe.py

@@ -129,7 +129,7 @@ if(!_isDuplicateGatewaySessionSnapshot([null, {session_id:'web-2', session_sourc
 def test_load_session_persists_only_after_metadata_loads():
     """Do not overwrite the last good localStorage sid before /api/session succeeds."""
     src = _read(SESSIONS_JS)
-    load = _block(src, "async function loadSession(sid)", "activeStreamId=S.session.active_stream_id")
+    load = _block(src, "async function loadSession(sid)", "function _mergePendingSessionMessage")
     api_pos = load.index("data = await api(`/api/session")
     persist_pos = load.index("localStorage.setItem('hermes-webui-session',S.session.session_id)")
 

tests/test_stale_stream_cleanup.py

@@ -435,7 +435,7 @@ def test_frontend_drops_inflight_cache_when_server_session_is_idle():
     # (preserved) cache-drop behavior in the now-nested form.
     marker = "If the server says the session is idle, reset browser-side streaming flags"
     marker_pos = SESSIONS_SRC.index(marker)
-    window = SESSIONS_SRC[marker_pos:marker_pos + 900]
+    window = SESSIONS_SRC[marker_pos:marker_pos + 1400]
     assert "if(!activeStreamId){" in window
     assert "S.busy=false" in window
     assert "S.activeStreamId=null" in window