fix errors with file watching and toolbar mode

.streamlit/config.toml

@@ -1,6 +1,12 @@
 [browser]
 gatherUsageStats       = false
 
+[server]
+fileWatcherType        = "none"
+
+[client]
+toolbarMode            = "viewer"
+
 [theme]
 base                   = "dark"
 primaryColor           = "#C9A84C"

streamlit_app.py

@@ -264,7 +264,11 @@ def _synthesis_gen(
     model: str,
     ctx: _StreamCtx,
 ) -> Generator[str, None, None]:
-    """Yield only the response-field tokens; populate ctx.full_text throughout."""
+    """Yield only the response-field tokens; populate ctx.full_text throughout.
+
+    We keep the last GUARD characters buffered at all times so that a marker
+    arriving split across multiple chunks never gets partially yielded to the UI.
+    """
     stream = client.chat.completions.create(
         model=model,
         messages=messages,
@@ -272,24 +276,38 @@ def _synthesis_gen(
         temperature=0.6,
         max_tokens=4096,
     )
+    GUARD = len(_SOURCES_MARKER)
     in_response = False
+    buf = ""  # response text buffered but not yet yielded
+
     for chunk in stream:
         delta = (chunk.choices[0].delta.content or "") if chunk.choices else ""
         ctx.full_text += delta
 
         if not in_response:
-            if _RESPONSE_MARKER in ctx.full_text:
-                in_response = True
-                after = ctx.full_text.split(_RESPONSE_MARKER, 1)[1].lstrip("\n")
-                if _SOURCES_MARKER in after:
-                    yield after.split(_SOURCES_MARKER, 1)[0].rstrip()
-                    return
-                if after:
-                    yield after
+            if _RESPONSE_MARKER not in ctx.full_text:
+                continue
+            in_response = True
+            buf = ctx.full_text.split(_RESPONSE_MARKER, 1)[1].lstrip("\n")
         else:
-            if _SOURCES_MARKER in ctx.full_text:
-                return
-            yield delta
+            buf += delta
+
+        # Sources marker has arrived — yield safe prefix and stop
+        if _SOURCES_MARKER in buf:
+            safe = buf.split(_SOURCES_MARKER, 1)[0].rstrip()
+            if safe:
+                yield safe
+            return
+
+        # Yield only the confirmed-safe portion; keep last GUARD chars buffered
+        # to guard against the marker arriving split across chunks
+        if len(buf) > GUARD:
+            yield buf[:-GUARD]
+            buf = buf[-GUARD:]
+
+    # Stream ended without a sources marker — flush remaining buffer
+    if in_response and buf:
+        yield buf.rstrip()
 
 
 def _explain_gen(