[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: channel
// goroutine_count: 2
// expected_nondeterminism: none
// description: goroutine reads from time.Ticker.C in a loop; main never calls ticker.Stop() and exits, leaving the goroutine permanently blocked on the ticker channel.

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() }()
			}
		}
	}

	ticker := time.NewTicker(10 * time.Millisecond)

	// Goroutine reads tick events. It will block on ticker.C between ticks.
	// BUG: main never calls ticker.Stop(); the goroutine is left alive and
	// permanently cycling between GoWaiting and GoRunnable when main exits.
	go func() {
		for t := range ticker.C {
			fmt.Println("tick at", t.UnixMilli())
		}
	}()

	// Let one tick fire so the goroutine runs at least once.
	time.Sleep(15 * time.Millisecond)

	// Exit without ticker.Stop() or closing ticker.C — goroutine leaks.
	time.Sleep(50 * time.Millisecond)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 29,
    "timestamp_ns": 14707493312192,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 30,
    "timestamp_ns": 14707503736000,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 31,
    "timestamp_ns": 14707503741184,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 32,
    "timestamp_ns": 14707503763520,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 33,
    "timestamp_ns": 14707503784896,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 34,
    "timestamp_ns": 14707503784960,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 35,
    "timestamp_ns": 14707503790272,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14707513741952,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14707513747712,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14707513770112,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "21": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "23": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "24": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 38,
  "timestamp_ns": 14707513770112,
  "event_type": "GoBlock",
  "goroutine_id": 24,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "21": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "23": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "24": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    }
  },
  "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": 10}


[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: channel
// goroutine_count: 2
// expected_nondeterminism: none
// description: goroutine reads from time.Ticker.C in a loop; main never calls ticker.Stop() and exits, leaving the goroutine permanently blocked on the ticker channel.

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() }()
			}
		}
	}

	ticker := time.NewTicker(10 * time.Millisecond)

	// Goroutine reads tick events. It will block on ticker.C between ticks.
	// BUG: main never calls ticker.Stop(); the goroutine is left alive and
	// permanently cycling between GoWaiting and GoRunnable when main exits.
	go func() {
		for t := range ticker.C {
			fmt.Println("tick at", t.UnixMilli())
		}
	}()

	// Let one tick fire so the goroutine runs at least once.
	time.Sleep(15 * time.Millisecond)

	// Exit without ticker.Stop() or closing ticker.C — goroutine leaks.
	time.Sleep(50 * time.Millisecond)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 29,
    "timestamp_ns": 14707493312192,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 30,
    "timestamp_ns": 14707503736000,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 31,
    "timestamp_ns": 14707503741184,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 32,
    "timestamp_ns": 14707503763520,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 33,
    "timestamp_ns": 14707503784896,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 34,
    "timestamp_ns": 14707503784960,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 35,
    "timestamp_ns": 14707503790272,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14707513741952,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14707513747712,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14707513770112,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "21": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "23": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "24": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 38,
  "timestamp_ns": 14707513770112,
  "event_type": "GoBlock",
  "goroutine_id": 24,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "21": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "23": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "24": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    }
  },
  "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": 8}


[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: channel
// goroutine_count: 2
// expected_nondeterminism: none
// description: goroutine reads from time.Ticker.C in a loop; main never calls ticker.Stop() and exits, leaving the goroutine permanently blocked on the ticker channel.

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() }()
			}
		}
	}

	ticker := time.NewTicker(10 * time.Millisecond)

	// Goroutine reads tick events. It will block on ticker.C between ticks.
	// BUG: main never calls ticker.Stop(); the goroutine is left alive and
	// permanently cycling between GoWaiting and GoRunnable when main exits.
	go func() {
		for t := range ticker.C {
			fmt.Println("tick at", t.UnixMilli())
		}
	}()

	// Let one tick fire so the goroutine runs at least once.
	time.Sleep(15 * time.Millisecond)

	// Exit without ticker.Stop() or closing ticker.C — goroutine leaks.
	time.Sleep(50 * time.Millisecond)
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 29,
    "timestamp_ns": 14707493312192,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 30,
    "timestamp_ns": 14707503736000,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 31,
    "timestamp_ns": 14707503741184,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 32,
    "timestamp_ns": 14707503763520,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 33,
    "timestamp_ns": 14707503784896,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 34,
    "timestamp_ns": 14707503784960,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 35,
    "timestamp_ns": 14707503790272,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14707513741952,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14707513747712,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14707513770112,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "21": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "23": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      },
      "24": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 38,
  "timestamp_ns": 14707513770112,
  "event_type": "GoBlock",
  "goroutine_id": 24,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "21": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "23": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    },
    "24": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    }
  },
  "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": 10}


[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: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 4,
    "timestamp_ns": 14718608335104,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14718608342912,
    "event_type": "GoCreate",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14718608348736,
    "event_type": "GoCreate",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14718608352064,
    "event_type": "GoCreate",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14718608355328,
    "event_type": "GoCreate",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14718608355904,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14718608358208,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14718608358720,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14718608374656,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14718608375168,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 13,
  "timestamp_ns": 14718608375168,
  "event_type": "GoStart",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "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": 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: leak
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 4,
    "timestamp_ns": 14718608335104,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14718608342912,
    "event_type": "GoCreate",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14718608348736,
    "event_type": "GoCreate",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14718608352064,
    "event_type": "GoCreate",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14718608355328,
    "event_type": "GoCreate",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14718608355904,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14718608358208,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14718608358720,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14718608374656,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14718608375168,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 13,
  "timestamp_ns": 14718608375168,
  "event_type": "GoStart",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "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": 23}


[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: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 4,
    "timestamp_ns": 14718608335104,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14718608342912,
    "event_type": "GoCreate",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14718608348736,
    "event_type": "GoCreate",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14718608352064,
    "event_type": "GoCreate",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14718608355328,
    "event_type": "GoCreate",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14718608355904,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14718608358208,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14718608358720,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14718608374656,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14718608375168,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 13,
  "timestamp_ns": 14718608375168,
  "event_type": "GoStart",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "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: leak
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 4,
    "timestamp_ns": 14718608335104,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14718608342912,
    "event_type": "GoCreate",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14718608348736,
    "event_type": "GoCreate",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14718608352064,
    "event_type": "GoCreate",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14718608355328,
    "event_type": "GoCreate",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14718608355904,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14718608358208,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14718608358720,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14718608374656,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14718608375168,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 13,
  "timestamp_ns": 14718608375168,
  "event_type": "GoStart",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "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": 11}


[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: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 4,
    "timestamp_ns": 14718608335104,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14718608342912,
    "event_type": "GoCreate",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14718608348736,
    "event_type": "GoCreate",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14718608352064,
    "event_type": "GoCreate",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14718608355328,
    "event_type": "GoCreate",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14718608355904,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14718608358208,
    "event_type": "GoBlock",
    "goroutine_id": 7,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14718608358720,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14718608374656,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14718608375168,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "11": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 13,
  "timestamp_ns": 14718608375168,
  "event_type": "GoStart",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "11": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "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": 24}


[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: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 17,
    "timestamp_ns": 14717394793152,
    "event_type": "GoStart",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14717394796288,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14717394797120,
    "event_type": "GoUnblock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14717394797568,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14717394797696,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14717394800896,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14717394800960,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14717394801408,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 25,
    "timestamp_ns": 14717394803584,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 26,
    "timestamp_ns": 14717394804992,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 26,
  "timestamp_ns": 14717394804992,
  "event_type": "GoBlock",
  "goroutine_id": 9,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    }
  },
  "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": "GoEnd", "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: leak
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 17,
    "timestamp_ns": 14717394793152,
    "event_type": "GoStart",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14717394796288,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14717394797120,
    "event_type": "GoUnblock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14717394797568,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14717394797696,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14717394800896,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14717394800960,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14717394801408,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 25,
    "timestamp_ns": 14717394803584,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 26,
    "timestamp_ns": 14717394804992,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 26,
  "timestamp_ns": 14717394804992,
  "event_type": "GoBlock",
  "goroutine_id": 9,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    }
  },
  "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": 25}


[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: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 17,
    "timestamp_ns": 14717394793152,
    "event_type": "GoStart",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14717394796288,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14717394797120,
    "event_type": "GoUnblock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14717394797568,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14717394797696,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14717394800896,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14717394800960,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14717394801408,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 25,
    "timestamp_ns": 14717394803584,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 26,
    "timestamp_ns": 14717394804992,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 26,
  "timestamp_ns": 14717394804992,
  "event_type": "GoBlock",
  "goroutine_id": 9,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    }
  },
  "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: leak
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 17,
    "timestamp_ns": 14717394793152,
    "event_type": "GoStart",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14717394796288,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14717394797120,
    "event_type": "GoUnblock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14717394797568,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14717394797696,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14717394800896,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14717394800960,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14717394801408,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 25,
    "timestamp_ns": 14717394803584,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 26,
    "timestamp_ns": 14717394804992,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 26,
  "timestamp_ns": 14717394804992,
  "event_type": "GoBlock",
  "goroutine_id": 9,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    }
  },
  "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: leak
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 17,
    "timestamp_ns": 14717394793152,
    "event_type": "GoStart",
    "goroutine_id": 9,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14717394796288,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14717394797120,
    "event_type": "GoUnblock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14717394797568,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14717394797696,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 22,
    "timestamp_ns": 14717394800896,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 23,
    "timestamp_ns": 14717394800960,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 24,
    "timestamp_ns": 14717394801408,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 25,
    "timestamp_ns": 14717394803584,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 26,
    "timestamp_ns": 14717394804992,
    "event_type": "GoBlock",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 26,
  "timestamp_ns": 14717394804992,
  "event_type": "GoBlock",
  "goroutine_id": 9,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    }
  },
  "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": 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: leak
// concurrency_pattern: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 31,
    "timestamp_ns": 14721036581056,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 32,
    "timestamp_ns": 14721036581696,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 33,
    "timestamp_ns": 14721037610176,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 34,
    "timestamp_ns": 14721037610432,
    "event_type": "GoUnblock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 35,
    "timestamp_ns": 14721037612608,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14721037617280,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14721037618944,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14721037622784,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14721037627776,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14721037628224,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "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"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "25": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 40,
  "timestamp_ns": 14721037628224,
  "event_type": "GoBlock",
  "goroutine_id": 22,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "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"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "25": {
      "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": "GoBlock", "goroutine_id": 23}


[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: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 31,
    "timestamp_ns": 14721036581056,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 32,
    "timestamp_ns": 14721036581696,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 33,
    "timestamp_ns": 14721037610176,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 34,
    "timestamp_ns": 14721037610432,
    "event_type": "GoUnblock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 35,
    "timestamp_ns": 14721037612608,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14721037617280,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14721037618944,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14721037622784,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14721037627776,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14721037628224,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "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"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "25": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 40,
  "timestamp_ns": 14721037628224,
  "event_type": "GoBlock",
  "goroutine_id": 22,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "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"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "25": {
      "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": "GoBlock", "goroutine_id": 10}


[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: pipeline
// goroutine_count: 4
// expected_nondeterminism: medium
// description: Pipeline pipeline stages stage1 -> stage2 -> stage3, leak_bug=True

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()
			// Bug: exit early after 1 item, leaving stage2 blocked
	val := <-inCh
	_ = val
	}(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": 31,
    "timestamp_ns": 14721036581056,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 32,
    "timestamp_ns": 14721036581696,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 33,
    "timestamp_ns": 14721037610176,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 34,
    "timestamp_ns": 14721037610432,
    "event_type": "GoUnblock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 35,
    "timestamp_ns": 14721037612608,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14721037617280,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14721037618944,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14721037622784,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14721037627776,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14721037628224,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "select",
        "locals_hint": "runtime.selectgo"
      },
      "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"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "25": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 40,
  "timestamp_ns": 14721037628224,
  "event_type": "GoBlock",
  "goroutine_id": 22,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "select",
      "locals_hint": "runtime.selectgo"
    },
    "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"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "25": {
      "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": 10}