[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: success
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=False

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				mu.Lock()
				sharedMap[id] = id * i
				mu.Unlock()
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 35,
    "timestamp_ns": 14729153081344,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14729153105536,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14729153107136,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14729153109760,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14729153110528,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14729153110720,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 41,
    "timestamp_ns": 14729153111424,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 42,
    "timestamp_ns": 14729153118208,
    "event_type": "GoUnblock",
    "goroutine_id": 25,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 43,
    "timestamp_ns": 14729153118656,
    "event_type": "GoUnblock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 44,
    "timestamp_ns": 14729153120512,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "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"
      },
      "24": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "25": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 44,
  "timestamp_ns": 14729153120512,
  "event_type": "GoStart",
  "goroutine_id": 23,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "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"
    },
    "24": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "25": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "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: success
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=False

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				mu.Lock()
				sharedMap[id] = id * i
				mu.Unlock()
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 35,
    "timestamp_ns": 14729153081344,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14729153105536,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14729153107136,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14729153109760,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14729153110528,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14729153110720,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 41,
    "timestamp_ns": 14729153111424,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 42,
    "timestamp_ns": 14729153118208,
    "event_type": "GoUnblock",
    "goroutine_id": 25,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 43,
    "timestamp_ns": 14729153118656,
    "event_type": "GoUnblock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 44,
    "timestamp_ns": 14729153120512,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "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"
      },
      "24": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "25": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 44,
  "timestamp_ns": 14729153120512,
  "event_type": "GoStart",
  "goroutine_id": 23,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "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"
    },
    "24": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "25": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: success
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=False

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				mu.Lock()
				sharedMap[id] = id * i
				mu.Unlock()
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 58,
    "timestamp_ns": 14731183441856,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 59,
    "timestamp_ns": 14731183442624,
    "event_type": "GoBlock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 60,
    "timestamp_ns": 14731183450688,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 61,
    "timestamp_ns": 14731183451584,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 62,
    "timestamp_ns": 14731183452096,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 63,
    "timestamp_ns": 14731183461952,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 64,
    "timestamp_ns": 14731183462784,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 65,
    "timestamp_ns": 14731183463232,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 66,
    "timestamp_ns": 14731183463488,
    "event_type": "GoUnblock",
    "goroutine_id": 25,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 67,
    "timestamp_ns": 14731183463552,
    "event_type": "GoStart",
    "goroutine_id": 25,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "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": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "24": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "25": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 67,
  "timestamp_ns": 14731183463552,
  "event_type": "GoStart",
  "goroutine_id": 25,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "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": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "24": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "25": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "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: success
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=False

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				mu.Lock()
				sharedMap[id] = id * i
				mu.Unlock()
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 58,
    "timestamp_ns": 14731183441856,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 59,
    "timestamp_ns": 14731183442624,
    "event_type": "GoBlock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 60,
    "timestamp_ns": 14731183450688,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 61,
    "timestamp_ns": 14731183451584,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 62,
    "timestamp_ns": 14731183452096,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 63,
    "timestamp_ns": 14731183461952,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 64,
    "timestamp_ns": 14731183462784,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 65,
    "timestamp_ns": 14731183463232,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 66,
    "timestamp_ns": 14731183463488,
    "event_type": "GoUnblock",
    "goroutine_id": 25,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 67,
    "timestamp_ns": 14731183463552,
    "event_type": "GoStart",
    "goroutine_id": 25,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "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": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "24": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "25": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 67,
  "timestamp_ns": 14731183463552,
  "event_type": "GoStart",
  "goroutine_id": 25,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "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": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "24": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "25": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "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: success
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=False

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				mu.Lock()
				sharedMap[id] = id * i
				mu.Unlock()
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 58,
    "timestamp_ns": 14731183441856,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 59,
    "timestamp_ns": 14731183442624,
    "event_type": "GoBlock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 60,
    "timestamp_ns": 14731183450688,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 61,
    "timestamp_ns": 14731183451584,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 62,
    "timestamp_ns": 14731183452096,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 63,
    "timestamp_ns": 14731183461952,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 64,
    "timestamp_ns": 14731183462784,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 65,
    "timestamp_ns": 14731183463232,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 66,
    "timestamp_ns": 14731183463488,
    "event_type": "GoUnblock",
    "goroutine_id": 25,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 67,
    "timestamp_ns": 14731183463552,
    "event_type": "GoStart",
    "goroutine_id": 25,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "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": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "24": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "25": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 67,
  "timestamp_ns": 14731183463552,
  "event_type": "GoStart",
  "goroutine_id": 25,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "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": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "24": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "25": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoUnblock", "goroutine_id": 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: success
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=False

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				mu.Lock()
				sharedMap[id] = id * i
				mu.Unlock()
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 58,
    "timestamp_ns": 14731183441856,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 59,
    "timestamp_ns": 14731183442624,
    "event_type": "GoBlock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 60,
    "timestamp_ns": 14731183450688,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 61,
    "timestamp_ns": 14731183451584,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 62,
    "timestamp_ns": 14731183452096,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 63,
    "timestamp_ns": 14731183461952,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 64,
    "timestamp_ns": 14731183462784,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 65,
    "timestamp_ns": 14731183463232,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 66,
    "timestamp_ns": 14731183463488,
    "event_type": "GoUnblock",
    "goroutine_id": 25,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 67,
    "timestamp_ns": 14731183463552,
    "event_type": "GoStart",
    "goroutine_id": 25,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "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": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "24": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "25": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 67,
  "timestamp_ns": 14731183463552,
  "event_type": "GoStart",
  "goroutine_id": 25,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "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": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "24": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "25": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "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: success
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=False

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				mu.Lock()
				sharedMap[id] = id * i
				mu.Unlock()
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 58,
    "timestamp_ns": 14731183441856,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 59,
    "timestamp_ns": 14731183442624,
    "event_type": "GoBlock",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 60,
    "timestamp_ns": 14731183450688,
    "event_type": "GoUnblock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 61,
    "timestamp_ns": 14731183451584,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 62,
    "timestamp_ns": 14731183452096,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 63,
    "timestamp_ns": 14731183461952,
    "event_type": "GoUnblock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 64,
    "timestamp_ns": 14731183462784,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 65,
    "timestamp_ns": 14731183463232,
    "event_type": "GoBlock",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 66,
    "timestamp_ns": 14731183463488,
    "event_type": "GoUnblock",
    "goroutine_id": 25,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 67,
    "timestamp_ns": 14731183463552,
    "event_type": "GoStart",
    "goroutine_id": 25,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "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": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "24": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "25": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 67,
  "timestamp_ns": 14731183463552,
  "event_type": "GoStart",
  "goroutine_id": 25,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "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": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "24": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "25": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "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": 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: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 12,
    "timestamp_ns": 14730294939200,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14730294940224,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14730294940736,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14730294942336,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14730294942784,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14730294947456,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14730294951232,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14730294953408,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14730295000960,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14730295003648,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "24": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "25": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 21,
  "timestamp_ns": 14730295003648,
  "event_type": "GoBlock",
  "goroutine_id": 21,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "24": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "25": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoStart", "goroutine_id": 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: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 12,
    "timestamp_ns": 14730294939200,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14730294940224,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14730294940736,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14730294942336,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14730294942784,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14730294947456,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14730294951232,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14730294953408,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14730295000960,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14730295003648,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "24": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "25": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 21,
  "timestamp_ns": 14730295003648,
  "event_type": "GoBlock",
  "goroutine_id": 21,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "24": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "25": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoBlock", "goroutine_id": 20}


[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: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 12,
    "timestamp_ns": 14730294939200,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14730294940224,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14730294940736,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14730294942336,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14730294942784,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14730294947456,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14730294951232,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14730294953408,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14730295000960,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14730295003648,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "24": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "25": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 21,
  "timestamp_ns": 14730295003648,
  "event_type": "GoBlock",
  "goroutine_id": 21,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "24": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "25": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoStart", "goroutine_id": 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: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 12,
    "timestamp_ns": 14730294939200,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14730294940224,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14730294940736,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14730294942336,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14730294942784,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14730294947456,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14730294951232,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14730294953408,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14730295000960,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14730295003648,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "24": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "25": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 21,
  "timestamp_ns": 14730295003648,
  "event_type": "GoBlock",
  "goroutine_id": 21,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "24": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "25": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoUnblock", "goroutine_id": 39}


[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: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 12,
    "timestamp_ns": 14730294939200,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14730294940224,
    "event_type": "GoBlock",
    "goroutine_id": 19,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14730294940736,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14730294942336,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14730294942784,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14730294947456,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14730294951232,
    "event_type": "GoBlock",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 19,
    "timestamp_ns": 14730294953408,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 20,
    "timestamp_ns": 14730295000960,
    "event_type": "GoStart",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 21,
    "timestamp_ns": 14730295003648,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "24": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "25": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 21,
  "timestamp_ns": 14730295003648,
  "event_type": "GoBlock",
  "goroutine_id": 21,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "24": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "25": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoStart", "goroutine_id": 13}


[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: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 35,
    "timestamp_ns": 14731310606272,
    "event_type": "GoStart",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14731310606656,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14731310609984,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14731310611328,
    "event_type": "GoUnblock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14731310611584,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14731310611776,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 41,
    "timestamp_ns": 14731310612672,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 42,
    "timestamp_ns": 14731310613184,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 43,
    "timestamp_ns": 14731310613568,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 44,
    "timestamp_ns": 14731310615744,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 44,
  "timestamp_ns": 14731310615744,
  "event_type": "GoBlock",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoUnblock", "goroutine_id": 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: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 35,
    "timestamp_ns": 14731310606272,
    "event_type": "GoStart",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14731310606656,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14731310609984,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14731310611328,
    "event_type": "GoUnblock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14731310611584,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14731310611776,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 41,
    "timestamp_ns": 14731310612672,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 42,
    "timestamp_ns": 14731310613184,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 43,
    "timestamp_ns": 14731310613568,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 44,
    "timestamp_ns": 14731310615744,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 44,
  "timestamp_ns": 14731310615744,
  "event_type": "GoBlock",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 35,
    "timestamp_ns": 14731310606272,
    "event_type": "GoStart",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14731310606656,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14731310609984,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14731310611328,
    "event_type": "GoUnblock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14731310611584,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14731310611776,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 41,
    "timestamp_ns": 14731310612672,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 42,
    "timestamp_ns": 14731310613184,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 43,
    "timestamp_ns": 14731310613568,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 44,
    "timestamp_ns": 14731310615744,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 44,
  "timestamp_ns": 14731310615744,
  "event_type": "GoBlock",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    }
  },
  "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: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 35,
    "timestamp_ns": 14731310606272,
    "event_type": "GoStart",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14731310606656,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14731310609984,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14731310611328,
    "event_type": "GoUnblock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14731310611584,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14731310611776,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 41,
    "timestamp_ns": 14731310612672,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 42,
    "timestamp_ns": 14731310613184,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 43,
    "timestamp_ns": 14731310613568,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 44,
    "timestamp_ns": 14731310615744,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 44,
  "timestamp_ns": 14731310615744,
  "event_type": "GoBlock",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoUnblock", "goroutine_id": 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: race
// concurrency_pattern: mutex
// goroutine_count: 5
// expected_nondeterminism: high
// description: Concurrent map access with W=4, race_bug=True

package main

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

	var mu sync.Mutex
	_ = mu // prevent declared and not used error
	sharedMap := make(map[int]int)
	var wg sync.WaitGroup

	for w := 0; w < 4; w++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for i := 0; i < 5; i++ {
				// lock omitted to trigger race
				sharedMap[id] = id * i
				// unlock omitted
				time.Sleep(time.Microsecond * 50)
			}
		}(w)
	}

	wg.Wait()
	fmt.Println("completed map writes, length:", len(sharedMap))
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 35,
    "timestamp_ns": 14731310606272,
    "event_type": "GoStart",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 36,
    "timestamp_ns": 14731310606656,
    "event_type": "GoBlock",
    "goroutine_id": 13,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 37,
    "timestamp_ns": 14731310609984,
    "event_type": "GoStart",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 38,
    "timestamp_ns": 14731310611328,
    "event_type": "GoUnblock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 39,
    "timestamp_ns": 14731310611584,
    "event_type": "GoStart",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 40,
    "timestamp_ns": 14731310611776,
    "event_type": "GoBlock",
    "goroutine_id": 11,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 41,
    "timestamp_ns": 14731310612672,
    "event_type": "GoBlock",
    "goroutine_id": 10,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 42,
    "timestamp_ns": 14731310613184,
    "event_type": "GoUnblock",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 43,
    "timestamp_ns": 14731310613568,
    "event_type": "GoStart",
    "goroutine_id": 12,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 44,
    "timestamp_ns": 14731310615744,
    "event_type": "GoBlock",
    "goroutine_id": 12,
    "goroutines": {
      "1": {
        "status": "blocked",
        "blocked_on": "sync",
        "locals_hint": "sync.(*WaitGroup).Wait"
      },
      "10": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "11": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "12": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "13": {
        "status": "blocked",
        "blocked_on": "sleep",
        "locals_hint": "time.Sleep"
      },
      "7": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "8": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "9": {
        "status": "blocked",
        "blocked_on": "system goroutine wait",
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 44,
  "timestamp_ns": 14731310615744,
  "event_type": "GoBlock",
  "goroutine_id": 12,
  "goroutines": {
    "1": {
      "status": "blocked",
      "blocked_on": "sync",
      "locals_hint": "sync.(*WaitGroup).Wait"
    },
    "10": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "11": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "12": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "13": {
      "status": "blocked",
      "blocked_on": "sleep",
      "locals_hint": "time.Sleep"
    },
    "7": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "8": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "9": {
      "status": "blocked",
      "blocked_on": "system goroutine wait",
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked.func1"
    }
  },
  "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": 20}