559 2026 01 27 Insert Before Stream Investigation 591f4e34

Research – insert_before_stream() Tool Panel Investigation

Date: 2026-01-27 Owner: claude-opus-4-5 Phase: Research

Goal

Investigate the insert_before_stream() implementation to understand why tool panels might not be appearing correctly during streaming, despite the reported fix.

Findings

Core Implementation

Location: /home/tuna/tunacode/src/tunacode/ui/widgets/chat.py:244-261

def insert_before_stream(self, renderable: RenderableType) -> None:
    """Insert a message before the current streaming widget."""
    widget = Static(renderable)
    widget.add_class("chat-message")

    if self._current_stream is not None:
        # Insert before the streaming widget
        self.mount(widget, before=self._current_stream)
    else:
        # No active stream, just append
        self.mount(widget)

    if self._auto_scroll:
        self.scroll_end(animate=False)

Usage: /home/tuna/tunacode/src/tunacode/ui/app.py:283

# Insert before streaming widget so tool panels appear inline
# without interrupting the stream
self.chat.insert_before_stream(panel)

Flow Analysis

Happy Path:
1. start_stream() → _current_stream = MessageWidget
2. Tokens stream → stream(chunk) → append()
3. Tool completes → ToolResultDisplay → insert_before_stream()
   → mount(widget, before=_current_stream) ✓ WORKS
4. end_stream() → finalize() → _current_stream = None

Identified Issues

HIGH: Cancel + Pending Tools Race Condition

Location: /home/tuna/tunacode/src/tunacode/ui/app.py:205-207

except asyncio.CancelledError:
    self.chat.cancel_stream()  # _current_stream = None
    self.notify("Cancelled")

Problem Sequence:

1. User cancels mid-tool-execution
2. cancel_stream() immediately sets _current_stream = None
3. Tools are still running in background (no cancellation signal)
4. Tool completes → posts ToolResultDisplay message
5. on_tool_result_display() → insert_before_stream(panel)
6. _current_stream is None → panel appends to end instead of inline

Visual Result: Tool panels appear AFTER the "Cancelled" notification, confusing users who expect cancellation to stop everything.

Evidence: cancel_stream() at chat.py:237-242 does not cancel pending tool executions:

def cancel_stream(self) -> None:
    if self._current_stream is not None:
        self._current_stream.remove()
        self._current_stream = None
    self.remove_class("streaming")
    # No tool cancellation logic

MEDIUM: Late Tool Panel After end_stream()

Location: /home/tuna/tunacode/src/tunacode/ui/app.py:238

Problem Sequence:

1. Model streams rapidly, finishes response
2. end_stream(panel) called at line 238
3. _current_stream = None (chat.py:231)
4. Slow tool (network delay) completes AFTER this
5. insert_before_stream() → _current_stream is None → appends to end

Visual Result: Tool panel appears BELOW the finalized agent response instead of inline where it belongs chronologically.

Key Observation

The insert_before_stream() design assumes all tools complete BEFORE the stream ends. This assumption breaks when:

• Tools have network latency
• User cancels mid-execution
• Parallel tools complete at different times

Tool Result Lifecycle (Confirmed)

Flow: core/agents/agent_components/orchestrator/orchestrator.py::_emit_tool_returns() → tool_result_callback (built in ui/repl_support.py::build_tool_result_callback) → app.post_message(ToolResultDisplay) → TextualReplApp.on_tool_result_display() → chat.insert_before_stream(panel).

Tool result panels are emitted when tool-return parts appear in a node’s request, not when the tool starts. This means delivery timing depends on when the tool return parts are surfaced to the UI loop.

Textual Mount Ordering (Confirmed)

Widget.mount(before=...) resolves a concrete parent + index and calls App._register(...), which inserts into parent._nodes via _insert(before, child) (Textual source in .venv/.../textual/widget.py and .venv/.../textual/app.py). Ordering is deterministic if the before widget is still attached to the same parent; if the streaming widget has been removed, insertion falls back to append in our code.

Message Queue Timing (Confirmed)

MessagePump.post_message() queues the message into an asyncio queue and returns immediately; handling happens later in _process_messages_loop() (.venv/.../textual/message_pump.py). Messages are not coalesced by default (Message.can_replace() returns False), so ToolResultDisplay is processed asynchronously relative to stream completion.

Related Files

• src/tunacode/ui/widgets/chat.py → ChatContainer, MessageWidget, insert_before_stream
• src/tunacode/ui/app.py:271-283 → on_tool_result_display handler
• src/tunacode/ui/app.py:205-207 → Cancel handling
• src/tunacode/core/agents/main.py:438-465 → Abort cleanup (message history only, no UI sync)
• memory-bank/research/2026-01-27_17-45-00_chatcontainer_refactor.md → Previous refactor research

Knowledge Gaps (Resolved)

1. Tool execution lifecycle - Tool results are emitted from _emit_tool_returns() during node processing; build_tool_result_callback() posts ToolResultDisplay, handled by TextualReplApp.on_tool_result_display().
2. Textual mount ordering - mount(before=widget) inserts into the parent’s node list at a specific index; ordering is deterministic while the reference widget remains mounted.
3. Message queue timing - post_message() queues to the message pump; delivery is async and can occur after stream end/cancel.

References

• chat.py:244-261 - insert_before_stream implementation
• app.py:205-207 - Cancel handling
• app.py:271-283 - Tool result display handler
• Previous research: memory-bank/research/2026-01-27_17-45-00_chatcontainer_refactor.md