Qwen3.6 Thinking-Only Guard — Pi Extension

Problem

Qwen3.6-27B (and similar thinking-capable models via providers like airouter) sometimes places tool calls inside the reasoning_content (thinking block) instead of as proper tool_calls in the API response.

• finish_reason: "stop" — model thinks it is done
• Thinking content contains <tool_call> ... </tool_call> blocks
• No actual tool_calls in response — pi does not execute them
• No text content — user sees empty or thinking-only response

Known issue: sgl-project/sglang#27021

Root Cause

Provider emits:

    reasoning_content: "<tool_call>
<function=read>
<parameter=path>
/home/reluxa/.profile
</parameter>
</function>
</tool_call>"
    content: ""
    finish_reason: "stop"

Pi's OpenAI-completions parser puts thinking in [type: "thinking"], finds no tool calls, and the turn ends. The model "stopped" from its perspective.

Solution: thinking-only-guard.ts

A pi extension that detects this pattern during live streaming and sends the trapped tool call(s) back to the model so it can execute them properly.

Files

File	Purpose
~/.pi/agent/extensions/thinking-only-guard.ts	The extension
~/.pi/agent/extensions/tests/thinking-only-guard.test.js	Unit tests (14 tests)

How It Works

1. message_update — Accumulates thinking_delta tokens into lastThinking
2. message_end — Checks if the completed assistant message matches the pattern:
   • toolCallCount >= 1 (one or more blocks in thinking)
   • hasText === false (no type: "text" in content array)
   • hasRealToolCalls === false (no type: "toolCall" in content array)
   • sawThinkingDelta === true (only fires during live streaming, not session replay)
3. If matched — extracts the exact tool call block(s) from thinking and sends a follow-up:

   Your last response had N tool call(s) inside your thinking block. Please execute them now:

   <function=read> /home/reluxa/.profile

4. turn_end — Resets retry counter
5. Max 2 retries per turn before giving up

Trigger Conditions

Condition	Must be
Tool calls in thinking	>= 1
Text blocks in content	0
Real toolCall entries	0
Live streaming	Yes
Retry count	< maxRetries (2)

Configuration

Editable at the top of the extension file.

Setting	Default	Notes
maxRetries	2	Max auto-continue per turn

Running Tests

node ~/.pi/agent/extensions/tests/thinking-only-guard.test.js

14 tests: single call, multiple calls, with text, with real toolCalls, plain thinking, empty thinking, extract N calls

Session Replay Results

Scanned 763 thinking-only messages across ~/.pi/agent/sessions/--home-reluxa--/. 4 would have triggered the guard (entries 50556cf1, 968d54e2, bf309c6e, 051b0538).

Design Decisions

Why send back as user message?

The turn is already finalized by message_end — pi will not re-scan for tool calls. Sending the trapped call back triggers a fresh turn where the model executes it.

Why not modify the message in-place?

message_end can return { message } to replace it, but the turn is already done. Converting thinking to text only makes the calls visible, not executable.

Why not a custom provider wrapper?

Technically possible — intercept raw streaming chunks, restructure reasoning_content into tool_calls. However: significantly more engineering, fragile (depends on provider internals). Current approach works and costs one extra turn.

Related

• Qwen3.6-27B on HuggingFace
• SGLang issue: stops after thinking
• LMStudio: thinking + tool call issue