fix(channels): prevent tool_calls from being dropped during streaming

[loafoe]

Summary

• Fix tool_calls messages being incorrectly filtered as auxiliary messages during streaming
• Add outboundMessageIsToolCalls() helper function
• Exclude tool_calls from auxiliary message filtering in preSend()

Problem

The auxiliary message filtering introduced in #2892 incorrectly drops tool_calls messages when:

1. There is an active stream for the chat
2. There is a tombstone from a recently finished stream (30-second window)

This causes tool_calls to not be delivered to the pico channel UI when users make consecutive requests, as the second request's tool_calls message arrives while the first request's stream is still active or within the tombstone window.

Root Cause

outboundMessageHasAuxiliaryKind() returns true for any message with message_kind set, which includes tool_calls. The filtering logic in preSend() then drops these messages to prevent stale feedback/thoughts from leaking after streaming.

However, tool_calls messages represent new tool invocations for the current turn - they are not stale auxiliary content and must be delivered to the UI.

Fix

Exclude tool_calls from auxiliary message filtering:

isToolCalls := outboundMessageIsToolCalls(msg)
if isAuxiliaryMessage && !isToolCalls {
    // filtering logic
}

Test plan

• Send consecutive tool-invoking requests via pico channel
• Verify all tool_calls messages are delivered to the UI
• Verify stale feedback/thoughts are still correctly filtered

🤖 Generated with Claude Code

[loafoe]

@imguoguo please check this one, it fixes a bug in the recently merged streaming which causes tool call messages to be dropped silently!