[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: select
// goroutine_count: 2
// expected_nondeterminism: low
// description: Select statement on unbuffered channel, leak_bug=True

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"time"
)

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	ch := make(chan int)

	go func() {
		// Simulate processing delay
		time.Sleep(time.Millisecond * 10)
		ch <- 42
	}()

	select {
	case val := <-ch:
		fmt.Println("received:", val)
	case <-time.After(1 * time.Millisecond):
		fmt.Println("timeout occurred")
	}

	// Small delay to allow the leaked goroutine to lock into GoWaiting block
	time.Sleep(time.Millisecond * 20)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14731235998144,
    "event_type": "GoCreate",
    "goroutine_id": 4,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14731236002112,
    "event_type": "GoCreate",
    "goroutine_id": 5,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "5": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14731236008960,
    "event_type": "GoStart",
    "goroutine_id": 4,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14731236019328,
    "event_type": "GoStart",
    "goroutine_id": 5,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14731236039744,
    "event_type": "GoCreate",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "6": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14731236044480,
    "event_type": "GoCreate",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "6": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14731236050752,
    "event_type": "GoStart",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14731236063040,
    "event_type": "GoBlock",
    "goroutine_id": 4,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14731236064064,
    "event_type": "GoBlock",
    "goroutine_id": 5,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14731236064960,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14731236065280,
    "event_type": "GoBlock",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14731236071616,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14731236077824,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14731236089280,
    "event_type": "GoUnblock",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14731236089344,
    "event_type": "GoStart",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 14,
  "timestamp_ns": 14731236089344,
  "event_type": "GoStart",
  "goroutine_id": 6,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "4": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoStart", "goroutine_id": 7}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: select
// goroutine_count: 2
// expected_nondeterminism: low
// description: Select statement on unbuffered channel, leak_bug=True

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"time"
)

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	ch := make(chan int)

	go func() {
		// Simulate processing delay
		time.Sleep(time.Millisecond * 10)
		ch <- 42
	}()

	select {
	case val := <-ch:
		fmt.Println("received:", val)
	case <-time.After(1 * time.Millisecond):
		fmt.Println("timeout occurred")
	}

	// Small delay to allow the leaked goroutine to lock into GoWaiting block
	time.Sleep(time.Millisecond * 20)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14731235998144,
    "event_type": "GoCreate",
    "goroutine_id": 4,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14731236002112,
    "event_type": "GoCreate",
    "goroutine_id": 5,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "5": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14731236008960,
    "event_type": "GoStart",
    "goroutine_id": 4,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14731236019328,
    "event_type": "GoStart",
    "goroutine_id": 5,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14731236039744,
    "event_type": "GoCreate",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "6": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14731236044480,
    "event_type": "GoCreate",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "6": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14731236050752,
    "event_type": "GoStart",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14731236063040,
    "event_type": "GoBlock",
    "goroutine_id": 4,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14731236064064,
    "event_type": "GoBlock",
    "goroutine_id": 5,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14731236064960,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14731236065280,
    "event_type": "GoBlock",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14731236071616,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14731236077824,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14731236089280,
    "event_type": "GoUnblock",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14731236089344,
    "event_type": "GoStart",
    "goroutine_id": 6,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 14,
  "timestamp_ns": 14731236089344,
  "event_type": "GoStart",
  "goroutine_id": 6,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "4": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoBlock", "goroutine_id": 22}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: select
// goroutine_count: 2
// expected_nondeterminism: low
// description: Select statement on unbuffered channel, leak_bug=True

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"time"
)

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	ch := make(chan int)

	go func() {
		// Simulate processing delay
		time.Sleep(time.Millisecond * 10)
		ch <- 42
	}()

	select {
	case val := <-ch:
		fmt.Println("received:", val)
	case <-time.After(1 * time.Millisecond):
		fmt.Println("timeout occurred")
	}

	// Small delay to allow the leaked goroutine to lock into GoWaiting block
	time.Sleep(time.Millisecond * 20)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 11,
    "timestamp_ns": 14733301791552,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14733301801728,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14733301802240,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14733301807296,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14733301808576,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14733301859136,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14733302877504,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14733302881600,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14733302908608,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14733302917184,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 20,
  "timestamp_ns": 14733302917184,
  "event_type": "GoUnblock",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoStart", "goroutine_id": 1}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: select
// goroutine_count: 2
// expected_nondeterminism: low
// description: Select statement on unbuffered channel, leak_bug=True

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"time"
)

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	ch := make(chan int)

	go func() {
		// Simulate processing delay
		time.Sleep(time.Millisecond * 10)
		ch <- 42
	}()

	select {
	case val := <-ch:
		fmt.Println("received:", val)
	case <-time.After(1 * time.Millisecond):
		fmt.Println("timeout occurred")
	}

	// Small delay to allow the leaked goroutine to lock into GoWaiting block
	time.Sleep(time.Millisecond * 20)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 11,
    "timestamp_ns": 14733301791552,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14733301801728,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14733301802240,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14733301807296,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14733301808576,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14733301859136,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14733302877504,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14733302881600,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14733302908608,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14733302917184,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 20,
  "timestamp_ns": 14733302917184,
  "event_type": "GoUnblock",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoStart", "goroutine_id": 1}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: select
// goroutine_count: 2
// expected_nondeterminism: low
// description: Select statement on unbuffered channel, leak_bug=True

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"time"
)

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	ch := make(chan int)

	go func() {
		// Simulate processing delay
		time.Sleep(time.Millisecond * 10)
		ch <- 42
	}()

	select {
	case val := <-ch:
		fmt.Println("received:", val)
	case <-time.After(1 * time.Millisecond):
		fmt.Println("timeout occurred")
	}

	// Small delay to allow the leaked goroutine to lock into GoWaiting block
	time.Sleep(time.Millisecond * 20)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 11,
    "timestamp_ns": 14733301791552,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14733301801728,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14733301802240,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14733301807296,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14733301808576,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14733301859136,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14733302877504,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14733302881600,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14733302908608,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14733302917184,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 20,
  "timestamp_ns": 14733302917184,
  "event_type": "GoUnblock",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoStart", "goroutine_id": 1}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: select
// goroutine_count: 2
// expected_nondeterminism: low
// description: Select statement on unbuffered channel, leak_bug=True

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"time"
)

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	ch := make(chan int)

	go func() {
		// Simulate processing delay
		time.Sleep(time.Millisecond * 10)
		ch <- 42
	}()

	select {
	case val := <-ch:
		fmt.Println("received:", val)
	case <-time.After(1 * time.Millisecond):
		fmt.Println("timeout occurred")
	}

	// Small delay to allow the leaked goroutine to lock into GoWaiting block
	time.Sleep(time.Millisecond * 20)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 11,
    "timestamp_ns": 14733301791552,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14733301801728,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14733301802240,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14733301807296,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14733301808576,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14733301859136,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14733302877504,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14733302881600,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14733302908608,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14733302917184,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 20,
  "timestamp_ns": 14733302917184,
  "event_type": "GoUnblock",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoStart", "goroutine_id": 1}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: select
// goroutine_count: 2
// expected_nondeterminism: low
// description: Select statement on unbuffered channel, leak_bug=True

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"time"
)

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	ch := make(chan int)

	go func() {
		// Simulate processing delay
		time.Sleep(time.Millisecond * 10)
		ch <- 42
	}()

	select {
	case val := <-ch:
		fmt.Println("received:", val)
	case <-time.After(1 * time.Millisecond):
		fmt.Println("timeout occurred")
	}

	// Small delay to allow the leaked goroutine to lock into GoWaiting block
	time.Sleep(time.Millisecond * 20)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 11,
    "timestamp_ns": 14733301791552,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14733301801728,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14733301802240,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14733301807296,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14733301808576,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14733301859136,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14733302877504,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14733302881600,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14733302908608,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14733302917184,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 20,
  "timestamp_ns": 14733302917184,
  "event_type": "GoUnblock",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoBlock", "goroutine_id": 1}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: success
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=False

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"sync"
	"time"
)

func stage1(out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 0; i < 5; i++ {
		out <- i
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func stage2(in <-chan int, out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for v := range in {
		out <- v * 2
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	var wg1, wg2, wg3 sync.WaitGroup
	ch1 := make(chan int)
	ch2 := make(chan int)

	wg1.Add(1)
	go stage1(ch1, &wg1)

	wg2.Add(1)
	go stage2(ch1, ch2, &wg2)

	wg3.Add(1)
	go func(inCh <-chan int) {
		defer wg3.Done()
		for range inCh { /* normal drain */ }
	}(ch2)

	// Exit harness
	done := make(chan struct{})
	go func() {
		wg1.Wait()
		wg2.Wait()
		wg3.Wait()
		close(done)
	}()

	select {
	case <-done:
		fmt.Println("pipeline done")
	case <-time.After(200 * time.Millisecond):
		fmt.Println("pipeline timeout")
	}
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 15,
    "timestamp_ns": 14734344324544,
    "event_type": "GoUnblock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14734344325248,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14734344325440,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14734344346624,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14734344415040,
    "event_type": "GoBlock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14734344421824,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14734344426368,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14734344428736,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14734344434112,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14734344435520,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "10": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "chan send",
        "locals_hint": "runtime.chansend1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 24,
  "timestamp_ns": 14734344435520,
  "event_type": "GoBlock",
  "goroutine_id": 7,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "10": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "chan send",
      "locals_hint": "runtime.chansend1"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoBlock", "goroutine_id": 1}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: success
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=False

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"sync"
	"time"
)

func stage1(out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 0; i < 5; i++ {
		out <- i
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func stage2(in <-chan int, out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for v := range in {
		out <- v * 2
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	var wg1, wg2, wg3 sync.WaitGroup
	ch1 := make(chan int)
	ch2 := make(chan int)

	wg1.Add(1)
	go stage1(ch1, &wg1)

	wg2.Add(1)
	go stage2(ch1, ch2, &wg2)

	wg3.Add(1)
	go func(inCh <-chan int) {
		defer wg3.Done()
		for range inCh { /* normal drain */ }
	}(ch2)

	// Exit harness
	done := make(chan struct{})
	go func() {
		wg1.Wait()
		wg2.Wait()
		wg3.Wait()
		close(done)
	}()

	select {
	case <-done:
		fmt.Println("pipeline done")
	case <-time.After(200 * time.Millisecond):
		fmt.Println("pipeline timeout")
	}
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 15,
    "timestamp_ns": 14734344324544,
    "event_type": "GoUnblock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14734344325248,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14734344325440,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14734344346624,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14734344415040,
    "event_type": "GoBlock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14734344421824,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14734344426368,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14734344428736,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14734344434112,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14734344435520,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "10": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "chan send",
        "locals_hint": "runtime.chansend1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 24,
  "timestamp_ns": 14734344435520,
  "event_type": "GoBlock",
  "goroutine_id": 7,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "10": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "chan send",
      "locals_hint": "runtime.chansend1"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoStart", "goroutine_id": 12}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: success
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=False

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"sync"
	"time"
)

func stage1(out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 0; i < 5; i++ {
		out <- i
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func stage2(in <-chan int, out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for v := range in {
		out <- v * 2
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	var wg1, wg2, wg3 sync.WaitGroup
	ch1 := make(chan int)
	ch2 := make(chan int)

	wg1.Add(1)
	go stage1(ch1, &wg1)

	wg2.Add(1)
	go stage2(ch1, ch2, &wg2)

	wg3.Add(1)
	go func(inCh <-chan int) {
		defer wg3.Done()
		for range inCh { /* normal drain */ }
	}(ch2)

	// Exit harness
	done := make(chan struct{})
	go func() {
		wg1.Wait()
		wg2.Wait()
		wg3.Wait()
		close(done)
	}()

	select {
	case <-done:
		fmt.Println("pipeline done")
	case <-time.After(200 * time.Millisecond):
		fmt.Println("pipeline timeout")
	}
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 15,
    "timestamp_ns": 14734344324544,
    "event_type": "GoUnblock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14734344325248,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14734344325440,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14734344346624,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14734344415040,
    "event_type": "GoBlock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14734344421824,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14734344426368,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14734344428736,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14734344434112,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14734344435520,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "10": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "chan send",
        "locals_hint": "runtime.chansend1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 24,
  "timestamp_ns": 14734344435520,
  "event_type": "GoBlock",
  "goroutine_id": 7,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "10": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "chan send",
      "locals_hint": "runtime.chansend1"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoStart", "goroutine_id": 37}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: success
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=False

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"sync"
	"time"
)

func stage1(out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 0; i < 5; i++ {
		out <- i
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func stage2(in <-chan int, out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for v := range in {
		out <- v * 2
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	var wg1, wg2, wg3 sync.WaitGroup
	ch1 := make(chan int)
	ch2 := make(chan int)

	wg1.Add(1)
	go stage1(ch1, &wg1)

	wg2.Add(1)
	go stage2(ch1, ch2, &wg2)

	wg3.Add(1)
	go func(inCh <-chan int) {
		defer wg3.Done()
		for range inCh { /* normal drain */ }
	}(ch2)

	// Exit harness
	done := make(chan struct{})
	go func() {
		wg1.Wait()
		wg2.Wait()
		wg3.Wait()
		close(done)
	}()

	select {
	case <-done:
		fmt.Println("pipeline done")
	case <-time.After(200 * time.Millisecond):
		fmt.Println("pipeline timeout")
	}
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 15,
    "timestamp_ns": 14734344324544,
    "event_type": "GoUnblock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14734344325248,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14734344325440,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14734344346624,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14734344415040,
    "event_type": "GoBlock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14734344421824,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14734344426368,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14734344428736,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14734344434112,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14734344435520,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "10": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "chan send",
        "locals_hint": "runtime.chansend1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 24,
  "timestamp_ns": 14734344435520,
  "event_type": "GoBlock",
  "goroutine_id": 7,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "10": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "chan send",
      "locals_hint": "runtime.chansend1"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoBlock", "goroutine_id": 9}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: success
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=False

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"sync"
	"time"
)

func stage1(out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 0; i < 5; i++ {
		out <- i
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func stage2(in <-chan int, out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for v := range in {
		out <- v * 2
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	var wg1, wg2, wg3 sync.WaitGroup
	ch1 := make(chan int)
	ch2 := make(chan int)

	wg1.Add(1)
	go stage1(ch1, &wg1)

	wg2.Add(1)
	go stage2(ch1, ch2, &wg2)

	wg3.Add(1)
	go func(inCh <-chan int) {
		defer wg3.Done()
		for range inCh { /* normal drain */ }
	}(ch2)

	// Exit harness
	done := make(chan struct{})
	go func() {
		wg1.Wait()
		wg2.Wait()
		wg3.Wait()
		close(done)
	}()

	select {
	case <-done:
		fmt.Println("pipeline done")
	case <-time.After(200 * time.Millisecond):
		fmt.Println("pipeline timeout")
	}
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 15,
    "timestamp_ns": 14734344324544,
    "event_type": "GoUnblock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14734344325248,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14734344325440,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14734344346624,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14734344415040,
    "event_type": "GoBlock",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14734344421824,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14734344426368,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14734344428736,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14734344434112,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14734344435520,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "10": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "chan send",
        "locals_hint": "runtime.chansend1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 24,
  "timestamp_ns": 14734344435520,
  "event_type": "GoBlock",
  "goroutine_id": 7,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "10": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "chan send",
      "locals_hint": "runtime.chansend1"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoBlock", "goroutine_id": 21}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: success
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=False

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"sync"
	"time"
)

func stage1(out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 0; i < 5; i++ {
		out <- i
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func stage2(in <-chan int, out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for v := range in {
		out <- v * 2
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	var wg1, wg2, wg3 sync.WaitGroup
	ch1 := make(chan int)
	ch2 := make(chan int)

	wg1.Add(1)
	go stage1(ch1, &wg1)

	wg2.Add(1)
	go stage2(ch1, ch2, &wg2)

	wg3.Add(1)
	go func(inCh <-chan int) {
		defer wg3.Done()
		for range inCh { /* normal drain */ }
	}(ch2)

	// Exit harness
	done := make(chan struct{})
	go func() {
		wg1.Wait()
		wg2.Wait()
		wg3.Wait()
		close(done)
	}()

	select {
	case <-done:
		fmt.Println("pipeline done")
	case <-time.After(200 * time.Millisecond):
		fmt.Println("pipeline timeout")
	}
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 42,
    "timestamp_ns": 14735369388416,
    "event_type": "GoStart",
    "goroutine_id": 40,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 43,
    "timestamp_ns": 14735369388672,
    "event_type": "GoBlock",
    "goroutine_id": 40,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 44,
    "timestamp_ns": 14735370506944,
    "event_type": "GoUnblock",
    "goroutine_id": 38,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 45,
    "timestamp_ns": 14735370507200,
    "event_type": "GoUnblock",
    "goroutine_id": 39,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 46,
    "timestamp_ns": 14735370509120,
    "event_type": "GoStart",
    "goroutine_id": 38,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 47,
    "timestamp_ns": 14735370509824,
    "event_type": "GoBlock",
    "goroutine_id": 38,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 48,
    "timestamp_ns": 14735370509952,
    "event_type": "GoStart",
    "goroutine_id": 39,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 49,
    "timestamp_ns": 14735370510720,
    "event_type": "GoUnblock",
    "goroutine_id": 38,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 50,
    "timestamp_ns": 14735370511168,
    "event_type": "GoUnblock",
    "goroutine_id": 40,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 51,
    "timestamp_ns": 14735370511360,
    "event_type": "GoBlock",
    "goroutine_id": 39,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "38": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.chanrecv2"
      },
      "39": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "40": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.chansend1"
      },
      "41": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 51,
  "timestamp_ns": 14735370511360,
  "event_type": "GoBlock",
  "goroutine_id": 39,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "35": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "36": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "37": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "38": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime.chanrecv2"
    },
    "39": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "40": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime.chansend1"
    },
    "41": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoStart", "goroutine_id": 40}


[System] You are a code execution simulator.

[User]
You are reasoning about concurrent Go program execution.

Here is a Go program:
<program>
// WEAVE_META
// outcome: success
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=False

package main

import (
	"fmt"
	"os"
	"runtime/trace"
	"sync"
	"time"
)

func stage1(out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 0; i < 5; i++ {
		out <- i
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func stage2(in <-chan int, out chan<- int, wg *sync.WaitGroup) {
	defer wg.Done()
	for v := range in {
		out <- v * 2
		time.Sleep(time.Millisecond * 1)
	}
	close(out)
}

func main() {
	if tf := os.Getenv("WEAVE_TRACE_FILE"); tf != "" {
		f, err := os.Create(tf)
		if err == nil {
			if err := trace.Start(f); err == nil {
				defer func() { trace.Stop(); f.Close() }()
			}
		}
	}

	var wg1, wg2, wg3 sync.WaitGroup
	ch1 := make(chan int)
	ch2 := make(chan int)

	wg1.Add(1)
	go stage1(ch1, &wg1)

	wg2.Add(1)
	go stage2(ch1, ch2, &wg2)

	wg3.Add(1)
	go func(inCh <-chan int) {
		defer wg3.Done()
		for range inCh { /* normal drain */ }
	}(ch2)

	// Exit harness
	done := make(chan struct{})
	go func() {
		wg1.Wait()
		wg2.Wait()
		wg3.Wait()
		close(done)
	}()

	select {
	case <-done:
		fmt.Println("pipeline done")
	case <-time.After(200 * time.Millisecond):
		fmt.Println("pipeline timeout")
	}
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 42,
    "timestamp_ns": 14735369388416,
    "event_type": "GoStart",
    "goroutine_id": 40,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 43,
    "timestamp_ns": 14735369388672,
    "event_type": "GoBlock",
    "goroutine_id": 40,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 44,
    "timestamp_ns": 14735370506944,
    "event_type": "GoUnblock",
    "goroutine_id": 38,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 45,
    "timestamp_ns": 14735370507200,
    "event_type": "GoUnblock",
    "goroutine_id": 39,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 46,
    "timestamp_ns": 14735370509120,
    "event_type": "GoStart",
    "goroutine_id": 38,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 47,
    "timestamp_ns": 14735370509824,
    "event_type": "GoBlock",
    "goroutine_id": 38,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 48,
    "timestamp_ns": 14735370509952,
    "event_type": "GoStart",
    "goroutine_id": 39,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 49,
    "timestamp_ns": 14735370510720,
    "event_type": "GoUnblock",
    "goroutine_id": 38,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 50,
    "timestamp_ns": 14735370511168,
    "event_type": "GoUnblock",
    "goroutine_id": 40,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 51,
    "timestamp_ns": 14735370511360,
    "event_type": "GoBlock",
    "goroutine_id": 39,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "38": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.chanrecv2"
      },
      "39": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "40": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.chansend1"
      },
      "41": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 51,
  "timestamp_ns": 14735370511360,
  "event_type": "GoBlock",
  "goroutine_id": 39,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "35": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "36": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "37": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "38": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime.chanrecv2"
    },
    "39": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "40": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime.chansend1"
    },
    "41": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

Predict the next scheduler event. What happens next?
Respond in JSON only — no markdown fences, no text outside the JSON object:
{"event_type":"GoStart|GoBlock|GoUnblock|GoCreate|GoEnd|GoSched","goroutine_id":<integer>,"reasoning":"<brief explanation>","confidence":"high|medium|low"}

[Assistant] {"event_type": "GoUnblock", "goroutine_id": 11}