Fix chat stream recovery and PDF library indexing (#468)

tests/test_chat_stream_scope.py

@@ -0,0 +1,19 @@
+from pathlib import Path
+
+
+def test_stream_render_helpers_are_visible_to_catch_block():
+    source = Path("static/js/chat.js").read_text(encoding="utf-8")
+    try_start = source.index("    try {\n      // Re-enable auto-scroll")
+    catch_start = source.index("    } catch (err) {", try_start)
+
+    outer_scope = source[:try_start]
+    try_body = source[try_start:catch_start]
+
+    assert "let _renderStream = () => {};" in outer_scope
+    assert "let _cancelThinkingTimer = () => {};" in outer_scope
+    assert "let _removeThinkingSpinner = () => {};" in outer_scope
+
+    assert "_renderStream = () => {" in try_body
+    assert "_cancelThinkingTimer = () => {" in try_body
+    assert "_removeThinkingSpinner = () => {" in try_body
+    assert "function _renderStream()" not in try_body