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fix(stapp): eliminate ghost duplicate of last text block on new message

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Root cause: stream loop emitted a bare st.empty() heartbeat per tick, accumulating
dozens of empty slots under chat_message. On the next rerun the history replay
path had no such slots, so Streamlit's incremental DOM diff misaligned and left
the previous render of the last text block as a grayed-out ghost.

Fix: unify streaming and history replay under the same shell
(slot = st.empty(); with slot.container(): render_segments(...)). Heartbeat now
re-enters the same slot each tick; when response is unchanged Streamlit's diff
is a no-op (no flicker), but the container() call still lets StopException
propagate so abort keeps working. Simplified render_segments from 5 params
(placeholders/rendered_cache/force_text) to 2 (segments, suffix).

Net: +19 -20 lines. Verified: no ghost, abort interrupts mid-stream, per-turn
fold-collapse preserved.
This commit is contained in:
Liang Jiaqing
2026-04-12 15:22:56 +08:00
parent d94e404f64
commit ecb8ac9a80
1 changed files with 19 additions and 20 deletions
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39
frontends/stapp.py
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@@ -89,21 +89,15 @@ def fold_turns(text):
segments.append({'type': 'fold', 'title': title, 'content': content})
else: segments.append({'type': 'text', 'content': marker + content})
return segments
def render_segments(segments, placeholders=None, rendered_cache=None, suffix='', force_text=False):
def _render_seg(target, seg, suf=''):
def render_segments(segments, suffix=''):
# 整块重画：调用方用 slot.container() 包裹，保证 DOM 路径稳定、跨 rerun 对齐（消除"灰色重影"）。
# heartbeat 空转时 segments 不变 → Streamlit 后端 diff 无变化 → 前端零闪烁；
# 但 container/markdown 本身是 API 调用，StopException 仍会被抛出（abort 照常起作用）。
for seg in segments:
if seg['type'] == 'fold':
with target.expander(seg['title'], expanded=False): st.markdown(seg['content'])
else: target.markdown(seg['content'] + suf, unsafe_allow_html=not not suf)
if placeholders is not None:
while len(placeholders) < len(segments):
placeholders.append(st.empty()); rendered_cache.append(None)
for i, seg in enumerate(segments):
if rendered_cache[i] != (seg, suffix):
if not force_text or seg['type'] == 'text':
with placeholders[i].container(): _render_seg(st, seg, suffix)
rendered_cache[i] = (seg, suffix)
else:
for seg in segments: _render_seg(st, seg)
with st.expander(seg['title'], expanded=False): st.markdown(seg['content'])
else:
st.markdown(seg['content'] + suffix, unsafe_allow_html=not not suffix)
def agent_backend_stream(prompt):
display_queue = agent.put_task(prompt, source="user")
@@ -123,8 +117,11 @@ def agent_backend_stream(prompt):
if "messages" not in st.session_state: st.session_state.messages = []
for msg in st.session_state.messages:
with st.chat_message(msg["role"]):
if msg["role"] == "assistant": render_segments(fold_turns(msg["content"]))
else: st.markdown(msg["content"])
# 用 slot=st.empty() + with slot.container(): ... 的外壳，DOM 路径和流式渲染完全一致，跨 rerun 对齐
slot = st.empty()
with slot.container():
if msg["role"] == "assistant": render_segments(fold_turns(msg["content"]))
else: st.markdown(msg["content"])
# IME composition fix (macOS only) - prevents Enter from submitting during CJK input
if os.name != 'nt':
@@ -136,11 +133,13 @@ if prompt := st.chat_input("请输入指令"):
with st.chat_message("user"): st.markdown(prompt)
with st.chat_message("assistant"):
turns = []; cache = []; response = ''
slot = st.empty(); response = ''
CURSOR = '<span style="animation: blink 1s step-start infinite; color: #0066cc;">▌</span><style>@keyframes blink { 50% { opacity: 0; } }</style>'
for response in agent_backend_stream(prompt):
render_segments(fold_turns(response), placeholders=turns, rendered_cache=cache, suffix='<span style="animation: blink 1s step-start infinite; color: #0066cc;">▌</span><style>@keyframes blink { 50% { opacity: 0; } }</style>')
st.empty() # force Streamlit to check StopException on every iteration (incl. heartbeat)
render_segments(fold_turns(response), placeholders=turns, rendered_cache=cache, force_text=True)
# 每轮整块重画（含 heartbeat 空转）：segments 不变时 Streamlit diff 零变更 → 不闪烁；
# 而 slot.container() 调用本身保证 Streamlit 能抛 StopException（abort 生效）
with slot.container(): render_segments(fold_turns(response), suffix=CURSOR)
with slot.container(): render_segments(fold_turns(response)) # 收尾去光标
st.session_state.messages.append({"role": "assistant", "content": response})
st.session_state.last_reply_time = int(time.time())