[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel cockroach_3710 (leak)

/*
 * Project: cockroach
 * Issue or PR  : https://github.com/cockroachdb/cockroach/pull/3710
 * Buggy version: 4afdd4860fd7c3bd9e92489f84a95e5cc7d11a0d
 * fix commit-id: cb65190f9caaf464723e7d072b1f1b69a044ef7b
 * Flaky: 2/100
 * Description: This deadlock is casued by acquiring a RLock twice in a call chain.
 * ForceRaftLogScanAndProcess(acquire s.mu.RLock()) ->MaybeAdd()->shouldQueue()->
 * getTruncatableIndexes()->RaftStatus(acquire s.mu.Rlock())
 */

package main

import (
	"os"
	"runtime/trace"
	"sync"
		"unsafe"
)

type Store struct {
	raftLogQueue *baseQueue
	replicas     map[int]*Replica

	mu struct {
		sync.RWMutex
	}
}

func (s *Store) ForceRaftLogScanAndProcess() {
	s.mu.RLock()
	for _, r := range s.replicas {
		s.raftLogQueue.MaybeAdd(r)
	}
	s.mu.RUnlock()
}

func (s *Store) RaftStatus() {
	s.mu.RLock()
	defer s.mu.RUnlock()
}

func (s *Store) processRaft() {
	go func() {
		for {
			var replicas []*Replica
			s.mu.Lock()
			for _, r := range s.replicas {
				replicas = append(replicas, r)
			}
			s.mu.Unlock()
			break
		}
	}()
}

type Replica struct {
	store *Store
}

type baseQueue struct {
	sync.Mutex
	impl *raftLogQueue
}

func (bq *baseQueue) MaybeAdd(repl *Replica) {
	bq.Lock()
	defer bq.Unlock()
	bq.impl.shouldQueue(repl)
}

type raftLogQueue struct{}

func (*raftLogQueue) shouldQueue(r *Replica) {
	getTruncatableIndexes(r)
}

func getTruncatableIndexes(r *Replica) {
	r.store.RaftStatus()
}

func NewStore() *Store {
	rlq := &raftLogQueue{}
	bq := &baseQueue{impl: rlq}
	store := &Store{
		raftLogQueue: bq,
		replicas:     make(map[int]*Replica),
	}
	r1 := &Replica{store}
	r2 := &Replica{store}

	makeKey := func(r *Replica) int {
		return int((uintptr(unsafe.Pointer(r)) >> 1) % 7)
	}
	store.replicas[makeKey(r1)] = r1
	store.replicas[makeKey(r2)] = r2

	return store
}

/// G1 										G2
/// store.ForceRaftLogScanAndProcess()
/// s.mu.RLock()
/// s.raftLogQueue.MaybeAdd()
/// bq.impl.shouldQueue()
/// getTruncatableIndexes()
/// r.store.RaftStatus()
/// 										store.processRaft()
/// 										s.mu.Lock()
/// s.mu.RLock()
/// ----------------------G1,G2 deadlock---------------------
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() }()
			}
		}
	}

	store := NewStore()
	go store.ForceRaftLogScanAndProcess() // G1
	go store.processRaft()                // G2
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 8,
    "timestamp_ns": 14742949700480,
    "event_type": "GoSched",
    "goroutine_id": 4,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14742949701312,
    "event_type": "GoStart",
    "goroutine_id": 4,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14742949706688,
    "event_type": "GoBlock",
    "goroutine_id": 4,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14742949707200,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14742949709696,
    "event_type": "GoStart",
    "goroutine_id": 5,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14742949711104,
    "event_type": "GoBlock",
    "goroutine_id": 5,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14742949713408,
    "event_type": "GoStart",
    "goroutine_id": 6,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14742949713472,
    "event_type": "GoCreate",
    "goroutine_id": 33,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14742949716736,
    "event_type": "GoEnd",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14742949717184,
    "event_type": "GoStart",
    "goroutine_id": 33,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "33": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 17,
  "timestamp_ns": 14742949717184,
  "event_type": "GoStart",
  "goroutine_id": 33,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "33": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "4": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    }
  },
  "channels": {},
  "mutexes": {}
}
</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: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel cockroach_3710 (leak)

/*
 * Project: cockroach
 * Issue or PR  : https://github.com/cockroachdb/cockroach/pull/3710
 * Buggy version: 4afdd4860fd7c3bd9e92489f84a95e5cc7d11a0d
 * fix commit-id: cb65190f9caaf464723e7d072b1f1b69a044ef7b
 * Flaky: 2/100
 * Description: This deadlock is casued by acquiring a RLock twice in a call chain.
 * ForceRaftLogScanAndProcess(acquire s.mu.RLock()) ->MaybeAdd()->shouldQueue()->
 * getTruncatableIndexes()->RaftStatus(acquire s.mu.Rlock())
 */

package main

import (
	"os"
	"runtime/trace"
	"sync"
		"unsafe"
)

type Store struct {
	raftLogQueue *baseQueue
	replicas     map[int]*Replica

	mu struct {
		sync.RWMutex
	}
}

func (s *Store) ForceRaftLogScanAndProcess() {
	s.mu.RLock()
	for _, r := range s.replicas {
		s.raftLogQueue.MaybeAdd(r)
	}
	s.mu.RUnlock()
}

func (s *Store) RaftStatus() {
	s.mu.RLock()
	defer s.mu.RUnlock()
}

func (s *Store) processRaft() {
	go func() {
		for {
			var replicas []*Replica
			s.mu.Lock()
			for _, r := range s.replicas {
				replicas = append(replicas, r)
			}
			s.mu.Unlock()
			break
		}
	}()
}

type Replica struct {
	store *Store
}

type baseQueue struct {
	sync.Mutex
	impl *raftLogQueue
}

func (bq *baseQueue) MaybeAdd(repl *Replica) {
	bq.Lock()
	defer bq.Unlock()
	bq.impl.shouldQueue(repl)
}

type raftLogQueue struct{}

func (*raftLogQueue) shouldQueue(r *Replica) {
	getTruncatableIndexes(r)
}

func getTruncatableIndexes(r *Replica) {
	r.store.RaftStatus()
}

func NewStore() *Store {
	rlq := &raftLogQueue{}
	bq := &baseQueue{impl: rlq}
	store := &Store{
		raftLogQueue: bq,
		replicas:     make(map[int]*Replica),
	}
	r1 := &Replica{store}
	r2 := &Replica{store}

	makeKey := func(r *Replica) int {
		return int((uintptr(unsafe.Pointer(r)) >> 1) % 7)
	}
	store.replicas[makeKey(r1)] = r1
	store.replicas[makeKey(r2)] = r2

	return store
}

/// G1 										G2
/// store.ForceRaftLogScanAndProcess()
/// s.mu.RLock()
/// s.raftLogQueue.MaybeAdd()
/// bq.impl.shouldQueue()
/// getTruncatableIndexes()
/// r.store.RaftStatus()
/// 										store.processRaft()
/// 										s.mu.Lock()
/// s.mu.RLock()
/// ----------------------G1,G2 deadlock---------------------
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() }()
			}
		}
	}

	store := NewStore()
	go store.ForceRaftLogScanAndProcess() // G1
	go store.processRaft()                // G2
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 8,
    "timestamp_ns": 14742949700480,
    "event_type": "GoSched",
    "goroutine_id": 4,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14742949701312,
    "event_type": "GoStart",
    "goroutine_id": 4,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14742949706688,
    "event_type": "GoBlock",
    "goroutine_id": 4,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14742949707200,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14742949709696,
    "event_type": "GoStart",
    "goroutine_id": 5,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14742949711104,
    "event_type": "GoBlock",
    "goroutine_id": 5,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14742949713408,
    "event_type": "GoStart",
    "goroutine_id": 6,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14742949713472,
    "event_type": "GoCreate",
    "goroutine_id": 33,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14742949716736,
    "event_type": "GoEnd",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14742949717184,
    "event_type": "GoStart",
    "goroutine_id": 33,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "33": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 17,
  "timestamp_ns": 14742949717184,
  "event_type": "GoStart",
  "goroutine_id": 33,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "33": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "4": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoEnd", "goroutine_id": 10}


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel cockroach_3710 (leak)

/*
 * Project: cockroach
 * Issue or PR  : https://github.com/cockroachdb/cockroach/pull/3710
 * Buggy version: 4afdd4860fd7c3bd9e92489f84a95e5cc7d11a0d
 * fix commit-id: cb65190f9caaf464723e7d072b1f1b69a044ef7b
 * Flaky: 2/100
 * Description: This deadlock is casued by acquiring a RLock twice in a call chain.
 * ForceRaftLogScanAndProcess(acquire s.mu.RLock()) ->MaybeAdd()->shouldQueue()->
 * getTruncatableIndexes()->RaftStatus(acquire s.mu.Rlock())
 */

package main

import (
	"os"
	"runtime/trace"
	"sync"
		"unsafe"
)

type Store struct {
	raftLogQueue *baseQueue
	replicas     map[int]*Replica

	mu struct {
		sync.RWMutex
	}
}

func (s *Store) ForceRaftLogScanAndProcess() {
	s.mu.RLock()
	for _, r := range s.replicas {
		s.raftLogQueue.MaybeAdd(r)
	}
	s.mu.RUnlock()
}

func (s *Store) RaftStatus() {
	s.mu.RLock()
	defer s.mu.RUnlock()
}

func (s *Store) processRaft() {
	go func() {
		for {
			var replicas []*Replica
			s.mu.Lock()
			for _, r := range s.replicas {
				replicas = append(replicas, r)
			}
			s.mu.Unlock()
			break
		}
	}()
}

type Replica struct {
	store *Store
}

type baseQueue struct {
	sync.Mutex
	impl *raftLogQueue
}

func (bq *baseQueue) MaybeAdd(repl *Replica) {
	bq.Lock()
	defer bq.Unlock()
	bq.impl.shouldQueue(repl)
}

type raftLogQueue struct{}

func (*raftLogQueue) shouldQueue(r *Replica) {
	getTruncatableIndexes(r)
}

func getTruncatableIndexes(r *Replica) {
	r.store.RaftStatus()
}

func NewStore() *Store {
	rlq := &raftLogQueue{}
	bq := &baseQueue{impl: rlq}
	store := &Store{
		raftLogQueue: bq,
		replicas:     make(map[int]*Replica),
	}
	r1 := &Replica{store}
	r2 := &Replica{store}

	makeKey := func(r *Replica) int {
		return int((uintptr(unsafe.Pointer(r)) >> 1) % 7)
	}
	store.replicas[makeKey(r1)] = r1
	store.replicas[makeKey(r2)] = r2

	return store
}

/// G1 										G2
/// store.ForceRaftLogScanAndProcess()
/// s.mu.RLock()
/// s.raftLogQueue.MaybeAdd()
/// bq.impl.shouldQueue()
/// getTruncatableIndexes()
/// r.store.RaftStatus()
/// 										store.processRaft()
/// 										s.mu.Lock()
/// s.mu.RLock()
/// ----------------------G1,G2 deadlock---------------------
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() }()
			}
		}
	}

	store := NewStore()
	go store.ForceRaftLogScanAndProcess() // G1
	go store.processRaft()                // G2
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 8,
    "timestamp_ns": 14742949700480,
    "event_type": "GoSched",
    "goroutine_id": 4,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14742949701312,
    "event_type": "GoStart",
    "goroutine_id": 4,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14742949706688,
    "event_type": "GoBlock",
    "goroutine_id": 4,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14742949707200,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14742949709696,
    "event_type": "GoStart",
    "goroutine_id": 5,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14742949711104,
    "event_type": "GoBlock",
    "goroutine_id": 5,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14742949713408,
    "event_type": "GoStart",
    "goroutine_id": 6,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14742949713472,
    "event_type": "GoCreate",
    "goroutine_id": 33,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14742949716736,
    "event_type": "GoEnd",
    "goroutine_id": 8,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14742949717184,
    "event_type": "GoStart",
    "goroutine_id": 33,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "33": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "4": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "5": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "6": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.main"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 17,
  "timestamp_ns": 14742949717184,
  "event_type": "GoStart",
  "goroutine_id": 33,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "33": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "4": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "5": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "6": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.main"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel etcd_7443 (leak)

package main

import (
	"os"
	"runtime/trace"
	"context"
	"sync"
	)

type addrConn struct {
	mu    sync.Mutex
	cc    *ClientConn
	addr  Address
	dopts dialOptions
	down  func()
}

func (ac *addrConn) tearDown() {
	ac.mu.Lock()
	defer ac.mu.Unlock()
	if ac.down != nil {
		ac.down()
		ac.down = nil
	}
}

func (ac *addrConn) resetTransport() {
	ac.mu.Lock()
	if ac.cc.dopts.balancer != nil {
		ac.down = ac.cc.dopts.balancer.Up(ac.addr)
	}
	ac.mu.Unlock()
}

type ClientConn struct {
	dopts dialOptions
	mu    sync.RWMutex
	conns map[Address]*addrConn
}

func (cc *ClientConn) lbWatcher() {
	for addrs := range cc.dopts.balancer.Notify() {
		var (
			add []Address
			del []*addrConn
		)
		cc.mu.Lock()
		for _, a := range addrs {
			if _, ok := cc.conns[a]; !ok {
				add = append(add, a)
			}
		}

		for k, c := range cc.conns {
			var keep bool
			for _, a := range addrs {
				if k == a {
					keep = true
					break
				}
			}
			if !keep {
				del = append(del, c)
				delete(cc.conns, c.addr)
			}
		}
		cc.mu.Unlock()
		for _, a := range add {
			cc.resetAddrConn(a)
		}
		for _, c := range del {
			c.tearDown()
		}
	}
}

func (cc *ClientConn) resetAddrConn(addr Address) {
	ac := &addrConn{
		cc:    cc,
		addr:  addr,
		dopts: cc.dopts,
	}
	cc.mu.Lock()
	if cc.conns == nil {
		cc.mu.Unlock()
		return
	}
	cc.conns[ac.addr] = ac
	cc.mu.Unlock()
	go func() {
		ac.resetTransport()
	}()
}

func (cc *ClientConn) Close() {
	cc.mu.Lock()
	conns := cc.conns
	cc.conns = nil
	cc.mu.Unlock()
	if cc.dopts.balancer != nil {
		cc.dopts.balancer.Close()
	}
	for _, ac := range conns {
		ac.tearDown()
	}
}

type dialOptions struct {
	balancer Balancer
}
type DialOption func(*dialOptions)

func Dial(opts ...DialOption) *ClientConn {
	return DialContext(context.Background(), opts...)
}

func DialContext(ctx context.Context, opts ...DialOption) *ClientConn {
	cc := &ClientConn{
		conns: make(map[Address]*addrConn),
	}
	for _, opt := range opts {
		opt(&cc.dopts)
	}
	go cc.lbWatcher()
	return cc
}

type Balancer interface {
	Up(addr Address) (down func())
	Notify() <-chan []Address
	Close()
}

type Address int

type simpleBalancer struct {
	addrs    []Address
	notifyCh chan []Address
	mu       sync.RWMutex
	closed   bool
	pinAddr  Address
}

func (b *simpleBalancer) Up(addr Address) func() {
	b.mu.Lock()
	defer b.mu.Unlock()

	if b.closed {
		return func() {}
	}

	if b.pinAddr == 0 {
		b.pinAddr = addr
		b.notifyCh <- []Address{addr}
	}

	return func() {
		defer func() {
			if r := recover(); r != nil {
				return
			}
		}()
		b.mu.Lock()
		defer b.mu.Unlock()
		if b.pinAddr == addr {
			b.pinAddr = 0
			b.notifyCh <- b.addrs
		}
	}
}

func (b *simpleBalancer) Notify() <-chan []Address {
	return b.notifyCh
}

func (b *simpleBalancer) Close() {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
		return
	}
	b.closed = true
	close(b.notifyCh)
	b.pinAddr = 0
}

func newSimpleBalancer() *simpleBalancer {
	notifyCh := make(chan []Address, 1)
	addrs := make([]Address, 3)
	for i := 0; i < 3; i++ {
		addrs[i] = Address(i)
	}
	notifyCh <- addrs
	return &simpleBalancer{
		addrs:    addrs,
		notifyCh: notifyCh,
	}
}

func WithBalancer(b Balancer) DialOption {
	return func(o *dialOptions) {
		o.balancer = b
	}
}
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() }()
			}
		}
	}

	sb := newSimpleBalancer()
	conn := Dial(WithBalancer(sb))

	closec := make(chan struct{})
	go func() {
		defer close(closec)
		sb.Close()
	}()
	go conn.Close()
	<-closec
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14754638508736,
    "event_type": "GoCreate",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14754638513024,
    "event_type": "GoCreate",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14754638513728,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14754638521088,
    "event_type": "GoCreate",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14754638531328,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14754638531328,
  "event_type": "GoStart",
  "goroutine_id": 20,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "20": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "21": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel etcd_7443 (leak)

package main

import (
	"os"
	"runtime/trace"
	"context"
	"sync"
	)

type addrConn struct {
	mu    sync.Mutex
	cc    *ClientConn
	addr  Address
	dopts dialOptions
	down  func()
}

func (ac *addrConn) tearDown() {
	ac.mu.Lock()
	defer ac.mu.Unlock()
	if ac.down != nil {
		ac.down()
		ac.down = nil
	}
}

func (ac *addrConn) resetTransport() {
	ac.mu.Lock()
	if ac.cc.dopts.balancer != nil {
		ac.down = ac.cc.dopts.balancer.Up(ac.addr)
	}
	ac.mu.Unlock()
}

type ClientConn struct {
	dopts dialOptions
	mu    sync.RWMutex
	conns map[Address]*addrConn
}

func (cc *ClientConn) lbWatcher() {
	for addrs := range cc.dopts.balancer.Notify() {
		var (
			add []Address
			del []*addrConn
		)
		cc.mu.Lock()
		for _, a := range addrs {
			if _, ok := cc.conns[a]; !ok {
				add = append(add, a)
			}
		}

		for k, c := range cc.conns {
			var keep bool
			for _, a := range addrs {
				if k == a {
					keep = true
					break
				}
			}
			if !keep {
				del = append(del, c)
				delete(cc.conns, c.addr)
			}
		}
		cc.mu.Unlock()
		for _, a := range add {
			cc.resetAddrConn(a)
		}
		for _, c := range del {
			c.tearDown()
		}
	}
}

func (cc *ClientConn) resetAddrConn(addr Address) {
	ac := &addrConn{
		cc:    cc,
		addr:  addr,
		dopts: cc.dopts,
	}
	cc.mu.Lock()
	if cc.conns == nil {
		cc.mu.Unlock()
		return
	}
	cc.conns[ac.addr] = ac
	cc.mu.Unlock()
	go func() {
		ac.resetTransport()
	}()
}

func (cc *ClientConn) Close() {
	cc.mu.Lock()
	conns := cc.conns
	cc.conns = nil
	cc.mu.Unlock()
	if cc.dopts.balancer != nil {
		cc.dopts.balancer.Close()
	}
	for _, ac := range conns {
		ac.tearDown()
	}
}

type dialOptions struct {
	balancer Balancer
}
type DialOption func(*dialOptions)

func Dial(opts ...DialOption) *ClientConn {
	return DialContext(context.Background(), opts...)
}

func DialContext(ctx context.Context, opts ...DialOption) *ClientConn {
	cc := &ClientConn{
		conns: make(map[Address]*addrConn),
	}
	for _, opt := range opts {
		opt(&cc.dopts)
	}
	go cc.lbWatcher()
	return cc
}

type Balancer interface {
	Up(addr Address) (down func())
	Notify() <-chan []Address
	Close()
}

type Address int

type simpleBalancer struct {
	addrs    []Address
	notifyCh chan []Address
	mu       sync.RWMutex
	closed   bool
	pinAddr  Address
}

func (b *simpleBalancer) Up(addr Address) func() {
	b.mu.Lock()
	defer b.mu.Unlock()

	if b.closed {
		return func() {}
	}

	if b.pinAddr == 0 {
		b.pinAddr = addr
		b.notifyCh <- []Address{addr}
	}

	return func() {
		defer func() {
			if r := recover(); r != nil {
				return
			}
		}()
		b.mu.Lock()
		defer b.mu.Unlock()
		if b.pinAddr == addr {
			b.pinAddr = 0
			b.notifyCh <- b.addrs
		}
	}
}

func (b *simpleBalancer) Notify() <-chan []Address {
	return b.notifyCh
}

func (b *simpleBalancer) Close() {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
		return
	}
	b.closed = true
	close(b.notifyCh)
	b.pinAddr = 0
}

func newSimpleBalancer() *simpleBalancer {
	notifyCh := make(chan []Address, 1)
	addrs := make([]Address, 3)
	for i := 0; i < 3; i++ {
		addrs[i] = Address(i)
	}
	notifyCh <- addrs
	return &simpleBalancer{
		addrs:    addrs,
		notifyCh: notifyCh,
	}
}

func WithBalancer(b Balancer) DialOption {
	return func(o *dialOptions) {
		o.balancer = b
	}
}
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() }()
			}
		}
	}

	sb := newSimpleBalancer()
	conn := Dial(WithBalancer(sb))

	closec := make(chan struct{})
	go func() {
		defer close(closec)
		sb.Close()
	}()
	go conn.Close()
	<-closec
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14754638508736,
    "event_type": "GoCreate",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14754638513024,
    "event_type": "GoCreate",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14754638513728,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14754638521088,
    "event_type": "GoCreate",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14754638531328,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14754638531328,
  "event_type": "GoStart",
  "goroutine_id": 20,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "20": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "21": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel etcd_7443 (leak)

package main

import (
	"os"
	"runtime/trace"
	"context"
	"sync"
	)

type addrConn struct {
	mu    sync.Mutex
	cc    *ClientConn
	addr  Address
	dopts dialOptions
	down  func()
}

func (ac *addrConn) tearDown() {
	ac.mu.Lock()
	defer ac.mu.Unlock()
	if ac.down != nil {
		ac.down()
		ac.down = nil
	}
}

func (ac *addrConn) resetTransport() {
	ac.mu.Lock()
	if ac.cc.dopts.balancer != nil {
		ac.down = ac.cc.dopts.balancer.Up(ac.addr)
	}
	ac.mu.Unlock()
}

type ClientConn struct {
	dopts dialOptions
	mu    sync.RWMutex
	conns map[Address]*addrConn
}

func (cc *ClientConn) lbWatcher() {
	for addrs := range cc.dopts.balancer.Notify() {
		var (
			add []Address
			del []*addrConn
		)
		cc.mu.Lock()
		for _, a := range addrs {
			if _, ok := cc.conns[a]; !ok {
				add = append(add, a)
			}
		}

		for k, c := range cc.conns {
			var keep bool
			for _, a := range addrs {
				if k == a {
					keep = true
					break
				}
			}
			if !keep {
				del = append(del, c)
				delete(cc.conns, c.addr)
			}
		}
		cc.mu.Unlock()
		for _, a := range add {
			cc.resetAddrConn(a)
		}
		for _, c := range del {
			c.tearDown()
		}
	}
}

func (cc *ClientConn) resetAddrConn(addr Address) {
	ac := &addrConn{
		cc:    cc,
		addr:  addr,
		dopts: cc.dopts,
	}
	cc.mu.Lock()
	if cc.conns == nil {
		cc.mu.Unlock()
		return
	}
	cc.conns[ac.addr] = ac
	cc.mu.Unlock()
	go func() {
		ac.resetTransport()
	}()
}

func (cc *ClientConn) Close() {
	cc.mu.Lock()
	conns := cc.conns
	cc.conns = nil
	cc.mu.Unlock()
	if cc.dopts.balancer != nil {
		cc.dopts.balancer.Close()
	}
	for _, ac := range conns {
		ac.tearDown()
	}
}

type dialOptions struct {
	balancer Balancer
}
type DialOption func(*dialOptions)

func Dial(opts ...DialOption) *ClientConn {
	return DialContext(context.Background(), opts...)
}

func DialContext(ctx context.Context, opts ...DialOption) *ClientConn {
	cc := &ClientConn{
		conns: make(map[Address]*addrConn),
	}
	for _, opt := range opts {
		opt(&cc.dopts)
	}
	go cc.lbWatcher()
	return cc
}

type Balancer interface {
	Up(addr Address) (down func())
	Notify() <-chan []Address
	Close()
}

type Address int

type simpleBalancer struct {
	addrs    []Address
	notifyCh chan []Address
	mu       sync.RWMutex
	closed   bool
	pinAddr  Address
}

func (b *simpleBalancer) Up(addr Address) func() {
	b.mu.Lock()
	defer b.mu.Unlock()

	if b.closed {
		return func() {}
	}

	if b.pinAddr == 0 {
		b.pinAddr = addr
		b.notifyCh <- []Address{addr}
	}

	return func() {
		defer func() {
			if r := recover(); r != nil {
				return
			}
		}()
		b.mu.Lock()
		defer b.mu.Unlock()
		if b.pinAddr == addr {
			b.pinAddr = 0
			b.notifyCh <- b.addrs
		}
	}
}

func (b *simpleBalancer) Notify() <-chan []Address {
	return b.notifyCh
}

func (b *simpleBalancer) Close() {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
		return
	}
	b.closed = true
	close(b.notifyCh)
	b.pinAddr = 0
}

func newSimpleBalancer() *simpleBalancer {
	notifyCh := make(chan []Address, 1)
	addrs := make([]Address, 3)
	for i := 0; i < 3; i++ {
		addrs[i] = Address(i)
	}
	notifyCh <- addrs
	return &simpleBalancer{
		addrs:    addrs,
		notifyCh: notifyCh,
	}
}

func WithBalancer(b Balancer) DialOption {
	return func(o *dialOptions) {
		o.balancer = b
	}
}
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() }()
			}
		}
	}

	sb := newSimpleBalancer()
	conn := Dial(WithBalancer(sb))

	closec := make(chan struct{})
	go func() {
		defer close(closec)
		sb.Close()
	}()
	go conn.Close()
	<-closec
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14754638508736,
    "event_type": "GoCreate",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14754638513024,
    "event_type": "GoCreate",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14754638513728,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14754638521088,
    "event_type": "GoCreate",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14754638531328,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14754638531328,
  "event_type": "GoStart",
  "goroutine_id": 20,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "20": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "21": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoCreate", "goroutine_id": 23}


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel etcd_7443 (leak)

package main

import (
	"os"
	"runtime/trace"
	"context"
	"sync"
	)

type addrConn struct {
	mu    sync.Mutex
	cc    *ClientConn
	addr  Address
	dopts dialOptions
	down  func()
}

func (ac *addrConn) tearDown() {
	ac.mu.Lock()
	defer ac.mu.Unlock()
	if ac.down != nil {
		ac.down()
		ac.down = nil
	}
}

func (ac *addrConn) resetTransport() {
	ac.mu.Lock()
	if ac.cc.dopts.balancer != nil {
		ac.down = ac.cc.dopts.balancer.Up(ac.addr)
	}
	ac.mu.Unlock()
}

type ClientConn struct {
	dopts dialOptions
	mu    sync.RWMutex
	conns map[Address]*addrConn
}

func (cc *ClientConn) lbWatcher() {
	for addrs := range cc.dopts.balancer.Notify() {
		var (
			add []Address
			del []*addrConn
		)
		cc.mu.Lock()
		for _, a := range addrs {
			if _, ok := cc.conns[a]; !ok {
				add = append(add, a)
			}
		}

		for k, c := range cc.conns {
			var keep bool
			for _, a := range addrs {
				if k == a {
					keep = true
					break
				}
			}
			if !keep {
				del = append(del, c)
				delete(cc.conns, c.addr)
			}
		}
		cc.mu.Unlock()
		for _, a := range add {
			cc.resetAddrConn(a)
		}
		for _, c := range del {
			c.tearDown()
		}
	}
}

func (cc *ClientConn) resetAddrConn(addr Address) {
	ac := &addrConn{
		cc:    cc,
		addr:  addr,
		dopts: cc.dopts,
	}
	cc.mu.Lock()
	if cc.conns == nil {
		cc.mu.Unlock()
		return
	}
	cc.conns[ac.addr] = ac
	cc.mu.Unlock()
	go func() {
		ac.resetTransport()
	}()
}

func (cc *ClientConn) Close() {
	cc.mu.Lock()
	conns := cc.conns
	cc.conns = nil
	cc.mu.Unlock()
	if cc.dopts.balancer != nil {
		cc.dopts.balancer.Close()
	}
	for _, ac := range conns {
		ac.tearDown()
	}
}

type dialOptions struct {
	balancer Balancer
}
type DialOption func(*dialOptions)

func Dial(opts ...DialOption) *ClientConn {
	return DialContext(context.Background(), opts...)
}

func DialContext(ctx context.Context, opts ...DialOption) *ClientConn {
	cc := &ClientConn{
		conns: make(map[Address]*addrConn),
	}
	for _, opt := range opts {
		opt(&cc.dopts)
	}
	go cc.lbWatcher()
	return cc
}

type Balancer interface {
	Up(addr Address) (down func())
	Notify() <-chan []Address
	Close()
}

type Address int

type simpleBalancer struct {
	addrs    []Address
	notifyCh chan []Address
	mu       sync.RWMutex
	closed   bool
	pinAddr  Address
}

func (b *simpleBalancer) Up(addr Address) func() {
	b.mu.Lock()
	defer b.mu.Unlock()

	if b.closed {
		return func() {}
	}

	if b.pinAddr == 0 {
		b.pinAddr = addr
		b.notifyCh <- []Address{addr}
	}

	return func() {
		defer func() {
			if r := recover(); r != nil {
				return
			}
		}()
		b.mu.Lock()
		defer b.mu.Unlock()
		if b.pinAddr == addr {
			b.pinAddr = 0
			b.notifyCh <- b.addrs
		}
	}
}

func (b *simpleBalancer) Notify() <-chan []Address {
	return b.notifyCh
}

func (b *simpleBalancer) Close() {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
		return
	}
	b.closed = true
	close(b.notifyCh)
	b.pinAddr = 0
}

func newSimpleBalancer() *simpleBalancer {
	notifyCh := make(chan []Address, 1)
	addrs := make([]Address, 3)
	for i := 0; i < 3; i++ {
		addrs[i] = Address(i)
	}
	notifyCh <- addrs
	return &simpleBalancer{
		addrs:    addrs,
		notifyCh: notifyCh,
	}
}

func WithBalancer(b Balancer) DialOption {
	return func(o *dialOptions) {
		o.balancer = b
	}
}
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() }()
			}
		}
	}

	sb := newSimpleBalancer()
	conn := Dial(WithBalancer(sb))

	closec := make(chan struct{})
	go func() {
		defer close(closec)
		sb.Close()
	}()
	go conn.Close()
	<-closec
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14754638508736,
    "event_type": "GoCreate",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14754638513024,
    "event_type": "GoCreate",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14754638513728,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14754638521088,
    "event_type": "GoCreate",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14754638531328,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14754638531328,
  "event_type": "GoStart",
  "goroutine_id": 20,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "20": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "21": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoBlock", "goroutine_id": 35}


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel etcd_7443 (leak)

package main

import (
	"os"
	"runtime/trace"
	"context"
	"sync"
	)

type addrConn struct {
	mu    sync.Mutex
	cc    *ClientConn
	addr  Address
	dopts dialOptions
	down  func()
}

func (ac *addrConn) tearDown() {
	ac.mu.Lock()
	defer ac.mu.Unlock()
	if ac.down != nil {
		ac.down()
		ac.down = nil
	}
}

func (ac *addrConn) resetTransport() {
	ac.mu.Lock()
	if ac.cc.dopts.balancer != nil {
		ac.down = ac.cc.dopts.balancer.Up(ac.addr)
	}
	ac.mu.Unlock()
}

type ClientConn struct {
	dopts dialOptions
	mu    sync.RWMutex
	conns map[Address]*addrConn
}

func (cc *ClientConn) lbWatcher() {
	for addrs := range cc.dopts.balancer.Notify() {
		var (
			add []Address
			del []*addrConn
		)
		cc.mu.Lock()
		for _, a := range addrs {
			if _, ok := cc.conns[a]; !ok {
				add = append(add, a)
			}
		}

		for k, c := range cc.conns {
			var keep bool
			for _, a := range addrs {
				if k == a {
					keep = true
					break
				}
			}
			if !keep {
				del = append(del, c)
				delete(cc.conns, c.addr)
			}
		}
		cc.mu.Unlock()
		for _, a := range add {
			cc.resetAddrConn(a)
		}
		for _, c := range del {
			c.tearDown()
		}
	}
}

func (cc *ClientConn) resetAddrConn(addr Address) {
	ac := &addrConn{
		cc:    cc,
		addr:  addr,
		dopts: cc.dopts,
	}
	cc.mu.Lock()
	if cc.conns == nil {
		cc.mu.Unlock()
		return
	}
	cc.conns[ac.addr] = ac
	cc.mu.Unlock()
	go func() {
		ac.resetTransport()
	}()
}

func (cc *ClientConn) Close() {
	cc.mu.Lock()
	conns := cc.conns
	cc.conns = nil
	cc.mu.Unlock()
	if cc.dopts.balancer != nil {
		cc.dopts.balancer.Close()
	}
	for _, ac := range conns {
		ac.tearDown()
	}
}

type dialOptions struct {
	balancer Balancer
}
type DialOption func(*dialOptions)

func Dial(opts ...DialOption) *ClientConn {
	return DialContext(context.Background(), opts...)
}

func DialContext(ctx context.Context, opts ...DialOption) *ClientConn {
	cc := &ClientConn{
		conns: make(map[Address]*addrConn),
	}
	for _, opt := range opts {
		opt(&cc.dopts)
	}
	go cc.lbWatcher()
	return cc
}

type Balancer interface {
	Up(addr Address) (down func())
	Notify() <-chan []Address
	Close()
}

type Address int

type simpleBalancer struct {
	addrs    []Address
	notifyCh chan []Address
	mu       sync.RWMutex
	closed   bool
	pinAddr  Address
}

func (b *simpleBalancer) Up(addr Address) func() {
	b.mu.Lock()
	defer b.mu.Unlock()

	if b.closed {
		return func() {}
	}

	if b.pinAddr == 0 {
		b.pinAddr = addr
		b.notifyCh <- []Address{addr}
	}

	return func() {
		defer func() {
			if r := recover(); r != nil {
				return
			}
		}()
		b.mu.Lock()
		defer b.mu.Unlock()
		if b.pinAddr == addr {
			b.pinAddr = 0
			b.notifyCh <- b.addrs
		}
	}
}

func (b *simpleBalancer) Notify() <-chan []Address {
	return b.notifyCh
}

func (b *simpleBalancer) Close() {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
		return
	}
	b.closed = true
	close(b.notifyCh)
	b.pinAddr = 0
}

func newSimpleBalancer() *simpleBalancer {
	notifyCh := make(chan []Address, 1)
	addrs := make([]Address, 3)
	for i := 0; i < 3; i++ {
		addrs[i] = Address(i)
	}
	notifyCh <- addrs
	return &simpleBalancer{
		addrs:    addrs,
		notifyCh: notifyCh,
	}
}

func WithBalancer(b Balancer) DialOption {
	return func(o *dialOptions) {
		o.balancer = b
	}
}
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() }()
			}
		}
	}

	sb := newSimpleBalancer()
	conn := Dial(WithBalancer(sb))

	closec := make(chan struct{})
	go func() {
		defer close(closec)
		sb.Close()
	}()
	go conn.Close()
	<-closec
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14754638508736,
    "event_type": "GoCreate",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14754638513024,
    "event_type": "GoCreate",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14754638513728,
    "event_type": "GoStart",
    "goroutine_id": 19,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14754638521088,
    "event_type": "GoCreate",
    "goroutine_id": 21,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14754638531328,
    "event_type": "GoStart",
    "goroutine_id": 20,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "20": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "21": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14754638531328,
  "event_type": "GoStart",
  "goroutine_id": 20,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "20": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "21": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel etcd_7443 (leak)

package main

import (
	"os"
	"runtime/trace"
	"context"
	"sync"
	)

type addrConn struct {
	mu    sync.Mutex
	cc    *ClientConn
	addr  Address
	dopts dialOptions
	down  func()
}

func (ac *addrConn) tearDown() {
	ac.mu.Lock()
	defer ac.mu.Unlock()
	if ac.down != nil {
		ac.down()
		ac.down = nil
	}
}

func (ac *addrConn) resetTransport() {
	ac.mu.Lock()
	if ac.cc.dopts.balancer != nil {
		ac.down = ac.cc.dopts.balancer.Up(ac.addr)
	}
	ac.mu.Unlock()
}

type ClientConn struct {
	dopts dialOptions
	mu    sync.RWMutex
	conns map[Address]*addrConn
}

func (cc *ClientConn) lbWatcher() {
	for addrs := range cc.dopts.balancer.Notify() {
		var (
			add []Address
			del []*addrConn
		)
		cc.mu.Lock()
		for _, a := range addrs {
			if _, ok := cc.conns[a]; !ok {
				add = append(add, a)
			}
		}

		for k, c := range cc.conns {
			var keep bool
			for _, a := range addrs {
				if k == a {
					keep = true
					break
				}
			}
			if !keep {
				del = append(del, c)
				delete(cc.conns, c.addr)
			}
		}
		cc.mu.Unlock()
		for _, a := range add {
			cc.resetAddrConn(a)
		}
		for _, c := range del {
			c.tearDown()
		}
	}
}

func (cc *ClientConn) resetAddrConn(addr Address) {
	ac := &addrConn{
		cc:    cc,
		addr:  addr,
		dopts: cc.dopts,
	}
	cc.mu.Lock()
	if cc.conns == nil {
		cc.mu.Unlock()
		return
	}
	cc.conns[ac.addr] = ac
	cc.mu.Unlock()
	go func() {
		ac.resetTransport()
	}()
}

func (cc *ClientConn) Close() {
	cc.mu.Lock()
	conns := cc.conns
	cc.conns = nil
	cc.mu.Unlock()
	if cc.dopts.balancer != nil {
		cc.dopts.balancer.Close()
	}
	for _, ac := range conns {
		ac.tearDown()
	}
}

type dialOptions struct {
	balancer Balancer
}
type DialOption func(*dialOptions)

func Dial(opts ...DialOption) *ClientConn {
	return DialContext(context.Background(), opts...)
}

func DialContext(ctx context.Context, opts ...DialOption) *ClientConn {
	cc := &ClientConn{
		conns: make(map[Address]*addrConn),
	}
	for _, opt := range opts {
		opt(&cc.dopts)
	}
	go cc.lbWatcher()
	return cc
}

type Balancer interface {
	Up(addr Address) (down func())
	Notify() <-chan []Address
	Close()
}

type Address int

type simpleBalancer struct {
	addrs    []Address
	notifyCh chan []Address
	mu       sync.RWMutex
	closed   bool
	pinAddr  Address
}

func (b *simpleBalancer) Up(addr Address) func() {
	b.mu.Lock()
	defer b.mu.Unlock()

	if b.closed {
		return func() {}
	}

	if b.pinAddr == 0 {
		b.pinAddr = addr
		b.notifyCh <- []Address{addr}
	}

	return func() {
		defer func() {
			if r := recover(); r != nil {
				return
			}
		}()
		b.mu.Lock()
		defer b.mu.Unlock()
		if b.pinAddr == addr {
			b.pinAddr = 0
			b.notifyCh <- b.addrs
		}
	}
}

func (b *simpleBalancer) Notify() <-chan []Address {
	return b.notifyCh
}

func (b *simpleBalancer) Close() {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
		return
	}
	b.closed = true
	close(b.notifyCh)
	b.pinAddr = 0
}

func newSimpleBalancer() *simpleBalancer {
	notifyCh := make(chan []Address, 1)
	addrs := make([]Address, 3)
	for i := 0; i < 3; i++ {
		addrs[i] = Address(i)
	}
	notifyCh <- addrs
	return &simpleBalancer{
		addrs:    addrs,
		notifyCh: notifyCh,
	}
}

func WithBalancer(b Balancer) DialOption {
	return func(o *dialOptions) {
		o.balancer = b
	}
}
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() }()
			}
		}
	}

	sb := newSimpleBalancer()
	conn := Dial(WithBalancer(sb))

	closec := make(chan struct{})
	go func() {
		defer close(closec)
		sb.Close()
	}()
	go conn.Close()
	<-closec
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 3,
    "timestamp_ns": 14751578112320,
    "event_type": "GoStart",
    "goroutine_id": 36,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14751578129408,
    "event_type": "GoCreate",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14751578133952,
    "event_type": "GoStart",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14751578147200,
    "event_type": "GoBlock",
    "goroutine_id": 35,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14751578151360,
    "event_type": "GoBlock",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14751578157120,
    "event_type": "GoBlock",
    "goroutine_id": 36,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14751578164736,
    "event_type": "GoUnblock",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14751578164800,
    "event_type": "GoStart",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14751578166272,
    "event_type": "GoCreate",
    "goroutine_id": 38,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "38": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.DialContext"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14751578166848,
    "event_type": "GoBlock",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "38": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.DialContext"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 12,
  "timestamp_ns": 14751578166848,
  "event_type": "GoBlock",
  "goroutine_id": 37,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "35": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "36": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "37": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "38": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.DialContext"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel etcd_7443 (leak)

package main

import (
	"os"
	"runtime/trace"
	"context"
	"sync"
	)

type addrConn struct {
	mu    sync.Mutex
	cc    *ClientConn
	addr  Address
	dopts dialOptions
	down  func()
}

func (ac *addrConn) tearDown() {
	ac.mu.Lock()
	defer ac.mu.Unlock()
	if ac.down != nil {
		ac.down()
		ac.down = nil
	}
}

func (ac *addrConn) resetTransport() {
	ac.mu.Lock()
	if ac.cc.dopts.balancer != nil {
		ac.down = ac.cc.dopts.balancer.Up(ac.addr)
	}
	ac.mu.Unlock()
}

type ClientConn struct {
	dopts dialOptions
	mu    sync.RWMutex
	conns map[Address]*addrConn
}

func (cc *ClientConn) lbWatcher() {
	for addrs := range cc.dopts.balancer.Notify() {
		var (
			add []Address
			del []*addrConn
		)
		cc.mu.Lock()
		for _, a := range addrs {
			if _, ok := cc.conns[a]; !ok {
				add = append(add, a)
			}
		}

		for k, c := range cc.conns {
			var keep bool
			for _, a := range addrs {
				if k == a {
					keep = true
					break
				}
			}
			if !keep {
				del = append(del, c)
				delete(cc.conns, c.addr)
			}
		}
		cc.mu.Unlock()
		for _, a := range add {
			cc.resetAddrConn(a)
		}
		for _, c := range del {
			c.tearDown()
		}
	}
}

func (cc *ClientConn) resetAddrConn(addr Address) {
	ac := &addrConn{
		cc:    cc,
		addr:  addr,
		dopts: cc.dopts,
	}
	cc.mu.Lock()
	if cc.conns == nil {
		cc.mu.Unlock()
		return
	}
	cc.conns[ac.addr] = ac
	cc.mu.Unlock()
	go func() {
		ac.resetTransport()
	}()
}

func (cc *ClientConn) Close() {
	cc.mu.Lock()
	conns := cc.conns
	cc.conns = nil
	cc.mu.Unlock()
	if cc.dopts.balancer != nil {
		cc.dopts.balancer.Close()
	}
	for _, ac := range conns {
		ac.tearDown()
	}
}

type dialOptions struct {
	balancer Balancer
}
type DialOption func(*dialOptions)

func Dial(opts ...DialOption) *ClientConn {
	return DialContext(context.Background(), opts...)
}

func DialContext(ctx context.Context, opts ...DialOption) *ClientConn {
	cc := &ClientConn{
		conns: make(map[Address]*addrConn),
	}
	for _, opt := range opts {
		opt(&cc.dopts)
	}
	go cc.lbWatcher()
	return cc
}

type Balancer interface {
	Up(addr Address) (down func())
	Notify() <-chan []Address
	Close()
}

type Address int

type simpleBalancer struct {
	addrs    []Address
	notifyCh chan []Address
	mu       sync.RWMutex
	closed   bool
	pinAddr  Address
}

func (b *simpleBalancer) Up(addr Address) func() {
	b.mu.Lock()
	defer b.mu.Unlock()

	if b.closed {
		return func() {}
	}

	if b.pinAddr == 0 {
		b.pinAddr = addr
		b.notifyCh <- []Address{addr}
	}

	return func() {
		defer func() {
			if r := recover(); r != nil {
				return
			}
		}()
		b.mu.Lock()
		defer b.mu.Unlock()
		if b.pinAddr == addr {
			b.pinAddr = 0
			b.notifyCh <- b.addrs
		}
	}
}

func (b *simpleBalancer) Notify() <-chan []Address {
	return b.notifyCh
}

func (b *simpleBalancer) Close() {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
		return
	}
	b.closed = true
	close(b.notifyCh)
	b.pinAddr = 0
}

func newSimpleBalancer() *simpleBalancer {
	notifyCh := make(chan []Address, 1)
	addrs := make([]Address, 3)
	for i := 0; i < 3; i++ {
		addrs[i] = Address(i)
	}
	notifyCh <- addrs
	return &simpleBalancer{
		addrs:    addrs,
		notifyCh: notifyCh,
	}
}

func WithBalancer(b Balancer) DialOption {
	return func(o *dialOptions) {
		o.balancer = b
	}
}
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() }()
			}
		}
	}

	sb := newSimpleBalancer()
	conn := Dial(WithBalancer(sb))

	closec := make(chan struct{})
	go func() {
		defer close(closec)
		sb.Close()
	}()
	go conn.Close()
	<-closec
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 3,
    "timestamp_ns": 14751578112320,
    "event_type": "GoStart",
    "goroutine_id": 36,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14751578129408,
    "event_type": "GoCreate",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14751578133952,
    "event_type": "GoStart",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14751578147200,
    "event_type": "GoBlock",
    "goroutine_id": 35,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14751578151360,
    "event_type": "GoBlock",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14751578157120,
    "event_type": "GoBlock",
    "goroutine_id": 36,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14751578164736,
    "event_type": "GoUnblock",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14751578164800,
    "event_type": "GoStart",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14751578166272,
    "event_type": "GoCreate",
    "goroutine_id": 38,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "38": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.DialContext"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14751578166848,
    "event_type": "GoBlock",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "38": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.DialContext"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 12,
  "timestamp_ns": 14751578166848,
  "event_type": "GoBlock",
  "goroutine_id": 37,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "35": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "36": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "37": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "38": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.DialContext"
    }
  },
  "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": 18}


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel etcd_7443 (leak)

package main

import (
	"os"
	"runtime/trace"
	"context"
	"sync"
	)

type addrConn struct {
	mu    sync.Mutex
	cc    *ClientConn
	addr  Address
	dopts dialOptions
	down  func()
}

func (ac *addrConn) tearDown() {
	ac.mu.Lock()
	defer ac.mu.Unlock()
	if ac.down != nil {
		ac.down()
		ac.down = nil
	}
}

func (ac *addrConn) resetTransport() {
	ac.mu.Lock()
	if ac.cc.dopts.balancer != nil {
		ac.down = ac.cc.dopts.balancer.Up(ac.addr)
	}
	ac.mu.Unlock()
}

type ClientConn struct {
	dopts dialOptions
	mu    sync.RWMutex
	conns map[Address]*addrConn
}

func (cc *ClientConn) lbWatcher() {
	for addrs := range cc.dopts.balancer.Notify() {
		var (
			add []Address
			del []*addrConn
		)
		cc.mu.Lock()
		for _, a := range addrs {
			if _, ok := cc.conns[a]; !ok {
				add = append(add, a)
			}
		}

		for k, c := range cc.conns {
			var keep bool
			for _, a := range addrs {
				if k == a {
					keep = true
					break
				}
			}
			if !keep {
				del = append(del, c)
				delete(cc.conns, c.addr)
			}
		}
		cc.mu.Unlock()
		for _, a := range add {
			cc.resetAddrConn(a)
		}
		for _, c := range del {
			c.tearDown()
		}
	}
}

func (cc *ClientConn) resetAddrConn(addr Address) {
	ac := &addrConn{
		cc:    cc,
		addr:  addr,
		dopts: cc.dopts,
	}
	cc.mu.Lock()
	if cc.conns == nil {
		cc.mu.Unlock()
		return
	}
	cc.conns[ac.addr] = ac
	cc.mu.Unlock()
	go func() {
		ac.resetTransport()
	}()
}

func (cc *ClientConn) Close() {
	cc.mu.Lock()
	conns := cc.conns
	cc.conns = nil
	cc.mu.Unlock()
	if cc.dopts.balancer != nil {
		cc.dopts.balancer.Close()
	}
	for _, ac := range conns {
		ac.tearDown()
	}
}

type dialOptions struct {
	balancer Balancer
}
type DialOption func(*dialOptions)

func Dial(opts ...DialOption) *ClientConn {
	return DialContext(context.Background(), opts...)
}

func DialContext(ctx context.Context, opts ...DialOption) *ClientConn {
	cc := &ClientConn{
		conns: make(map[Address]*addrConn),
	}
	for _, opt := range opts {
		opt(&cc.dopts)
	}
	go cc.lbWatcher()
	return cc
}

type Balancer interface {
	Up(addr Address) (down func())
	Notify() <-chan []Address
	Close()
}

type Address int

type simpleBalancer struct {
	addrs    []Address
	notifyCh chan []Address
	mu       sync.RWMutex
	closed   bool
	pinAddr  Address
}

func (b *simpleBalancer) Up(addr Address) func() {
	b.mu.Lock()
	defer b.mu.Unlock()

	if b.closed {
		return func() {}
	}

	if b.pinAddr == 0 {
		b.pinAddr = addr
		b.notifyCh <- []Address{addr}
	}

	return func() {
		defer func() {
			if r := recover(); r != nil {
				return
			}
		}()
		b.mu.Lock()
		defer b.mu.Unlock()
		if b.pinAddr == addr {
			b.pinAddr = 0
			b.notifyCh <- b.addrs
		}
	}
}

func (b *simpleBalancer) Notify() <-chan []Address {
	return b.notifyCh
}

func (b *simpleBalancer) Close() {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
		return
	}
	b.closed = true
	close(b.notifyCh)
	b.pinAddr = 0
}

func newSimpleBalancer() *simpleBalancer {
	notifyCh := make(chan []Address, 1)
	addrs := make([]Address, 3)
	for i := 0; i < 3; i++ {
		addrs[i] = Address(i)
	}
	notifyCh <- addrs
	return &simpleBalancer{
		addrs:    addrs,
		notifyCh: notifyCh,
	}
}

func WithBalancer(b Balancer) DialOption {
	return func(o *dialOptions) {
		o.balancer = b
	}
}
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() }()
			}
		}
	}

	sb := newSimpleBalancer()
	conn := Dial(WithBalancer(sb))

	closec := make(chan struct{})
	go func() {
		defer close(closec)
		sb.Close()
	}()
	go conn.Close()
	<-closec
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 3,
    "timestamp_ns": 14751578112320,
    "event_type": "GoStart",
    "goroutine_id": 36,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14751578129408,
    "event_type": "GoCreate",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 5,
    "timestamp_ns": 14751578133952,
    "event_type": "GoStart",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 6,
    "timestamp_ns": 14751578147200,
    "event_type": "GoBlock",
    "goroutine_id": 35,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 7,
    "timestamp_ns": 14751578151360,
    "event_type": "GoBlock",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "37": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 8,
    "timestamp_ns": 14751578157120,
    "event_type": "GoBlock",
    "goroutine_id": 36,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 9,
    "timestamp_ns": 14751578164736,
    "event_type": "GoUnblock",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14751578164800,
    "event_type": "GoStart",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14751578166272,
    "event_type": "GoCreate",
    "goroutine_id": 38,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "38": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.DialContext"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14751578166848,
    "event_type": "GoBlock",
    "goroutine_id": 37,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "35": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "36": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "37": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "38": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "main.DialContext"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 12,
  "timestamp_ns": 14751578166848,
  "event_type": "GoBlock",
  "goroutine_id": 37,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "35": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "36": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "37": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "38": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "main.DialContext"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoEnd", "goroutine_id": 24}