[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": "GoUnblock", "goroutine_id": 1}


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: 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": "GoBlock", "goroutine_id": 20}


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: 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": 9,
    "timestamp_ns": 14753624702848,
    "event_type": "GoCreate",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14753624703424,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14753624706368,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14753624706816,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14753624717568,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14753624718336,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14753624725952,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14753624726400,
    "event_type": "GoEnd",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14753624729600,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14753624730560,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 18,
  "timestamp_ns": 14753624730560,
  "event_type": "GoStart",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoEnd", "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": 9,
    "timestamp_ns": 14753624702848,
    "event_type": "GoCreate",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14753624703424,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14753624706368,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14753624706816,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14753624717568,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14753624718336,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14753624725952,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14753624726400,
    "event_type": "GoEnd",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14753624729600,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14753624730560,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 18,
  "timestamp_ns": 14753624730560,
  "event_type": "GoStart",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: 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": 9,
    "timestamp_ns": 14753624702848,
    "event_type": "GoCreate",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14753624703424,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14753624706368,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14753624706816,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14753624717568,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14753624718336,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14753624725952,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14753624726400,
    "event_type": "GoEnd",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14753624729600,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14753624730560,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 18,
  "timestamp_ns": 14753624730560,
  "event_type": "GoStart",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: 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": 9,
    "timestamp_ns": 14753624702848,
    "event_type": "GoCreate",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14753624703424,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14753624706368,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14753624706816,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14753624717568,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14753624718336,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14753624725952,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14753624726400,
    "event_type": "GoEnd",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14753624729600,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14753624730560,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 18,
  "timestamp_ns": 14753624730560,
  "event_type": "GoStart",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: leak
// concurrency_pattern: 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": 9,
    "timestamp_ns": 14753624702848,
    "event_type": "GoCreate",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 10,
    "timestamp_ns": 14753624703424,
    "event_type": "GoStart",
    "goroutine_id": 22,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 11,
    "timestamp_ns": 14753624706368,
    "event_type": "GoBlock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 12,
    "timestamp_ns": 14753624706816,
    "event_type": "GoStart",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 13,
    "timestamp_ns": 14753624717568,
    "event_type": "GoBlock",
    "goroutine_id": 20,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 14,
    "timestamp_ns": 14753624718336,
    "event_type": "GoStart",
    "goroutine_id": 23,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 15,
    "timestamp_ns": 14753624725952,
    "event_type": "GoBlock",
    "goroutine_id": 21,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 16,
    "timestamp_ns": 14753624726400,
    "event_type": "GoEnd",
    "goroutine_id": 24,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 17,
    "timestamp_ns": 14753624729600,
    "event_type": "GoUnblock",
    "goroutine_id": 1,
    "goroutines": "... [TRUNCATED FOR LENGTH] ...",
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 18,
    "timestamp_ns": 14753624730560,
    "event_type": "GoStart",
    "goroutine_id": 1,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "19": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "20": {
        "status": "blocked",
        "blocked_on": "chan receive",
        "locals_hint": "runtime.chanrecv1"
      },
      "21": {
        "status": "running",
        "blocked_on": "syscall",
        "locals_hint": "syscall.syscall"
      },
      "22": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "23": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 18,
  "timestamp_ns": 14753624730560,
  "event_type": "GoStart",
  "goroutine_id": 1,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "19": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "20": {
      "status": "blocked",
      "blocked_on": "chan receive",
      "locals_hint": "runtime.chanrecv1"
    },
    "21": {
      "status": "running",
      "blocked_on": "syscall",
      "locals_hint": "syscall.syscall"
    },
    "22": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "23": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: race
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel grpc_1748 (race)

package main

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

var minConnectTimeout = 10 * time.Second

var balanceMutex sync.Mutex // We add this for avoiding other data race

type Balancer interface {
	HandleResolvedAddrs()
}

type Builder interface {
	Build(cc balancer_ClientConn) Balancer
}

func newPickfirstBuilder() Builder {
	return &pickfirstBuilder{}
}

type pickfirstBuilder struct{}

func (*pickfirstBuilder) Build(cc balancer_ClientConn) Balancer {
	return &pickfirstBalancer{cc: cc}
}

type SubConn interface {
	Connect()
}

type balancer_ClientConn interface {
	NewSubConn() SubConn
}

type pickfirstBalancer struct {
	cc balancer_ClientConn
	sc SubConn
}

func (b *pickfirstBalancer) HandleResolvedAddrs() {
	b.sc = b.cc.NewSubConn()
	b.sc.Connect()
}

type pickerWrapper struct {
	mu sync.Mutex
}

type acBalancerWrapper struct {
	mu sync.Mutex
	ac *addrConn
}

type addrConn struct {
	cc   *ClientConn
	acbw SubConn
	mu   sync.Mutex
}

func (ac *addrConn) resetTransport() {
	_ = minConnectTimeout
}

func (ac *addrConn) transportMonitor() {
	ac.resetTransport()
}

func (ac *addrConn) connect() {
	go func() {
		ac.transportMonitor()
	}()
}

func (acbw *acBalancerWrapper) Connect() {
	acbw.mu.Lock()
	defer acbw.mu.Unlock()
	acbw.ac.connect()
}

func newPickerWrapper() *pickerWrapper {
	return &pickerWrapper{}
}

type ClientConn struct {
	mu sync.Mutex
}

func (cc *ClientConn) switchBalancer() {
	builder := newPickfirstBuilder()
	newCCBalancerWrapper(cc, builder)
}

func (cc *ClientConn) newAddrConn() *addrConn {
	return &addrConn{cc: cc}
}

type ccBalancerWrapper struct {
	cc       *ClientConn
	balancer Balancer
}

func (ccb *ccBalancerWrapper) watcher() {
	for i := 0; i < 10; i++ {
		balanceMutex.Lock()
		if ccb.balancer != nil {
			balanceMutex.Unlock()
			ccb.balancer.HandleResolvedAddrs()
		} else {
			balanceMutex.Unlock()
		}
	}
}

func (ccb *ccBalancerWrapper) NewSubConn() SubConn {
	ac := ccb.cc.newAddrConn()
	acbw := &acBalancerWrapper{ac: ac}
	acbw.ac.mu.Lock()
	ac.acbw = acbw
	acbw.ac.mu.Unlock()
	return acbw
}

func newCCBalancerWrapper(cc *ClientConn, b Builder) {
	ccb := &ccBalancerWrapper{cc: cc}
	go ccb.watcher()
	balanceMutex.Lock()
	defer balanceMutex.Unlock()
	ccb.balancer = b.Build(ccb)
}

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

	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		mctBkp := minConnectTimeout
		// Call this only after transportMonitor goroutine has ended.
		defer func() {
			minConnectTimeout = mctBkp
		}()
		cc := &ClientConn{}
		cc.switchBalancer()
	}()
	wg.Wait()
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14762383879680,
    "event_type": "GoCreate",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14762383886720,
    "event_type": "GoCreate",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14762383888704,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14762383899456,
    "event_type": "GoCreate",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14762383899776,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14762383899776,
  "event_type": "GoStart",
  "goroutine_id": 8,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: race
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel grpc_1748 (race)

package main

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

var minConnectTimeout = 10 * time.Second

var balanceMutex sync.Mutex // We add this for avoiding other data race

type Balancer interface {
	HandleResolvedAddrs()
}

type Builder interface {
	Build(cc balancer_ClientConn) Balancer
}

func newPickfirstBuilder() Builder {
	return &pickfirstBuilder{}
}

type pickfirstBuilder struct{}

func (*pickfirstBuilder) Build(cc balancer_ClientConn) Balancer {
	return &pickfirstBalancer{cc: cc}
}

type SubConn interface {
	Connect()
}

type balancer_ClientConn interface {
	NewSubConn() SubConn
}

type pickfirstBalancer struct {
	cc balancer_ClientConn
	sc SubConn
}

func (b *pickfirstBalancer) HandleResolvedAddrs() {
	b.sc = b.cc.NewSubConn()
	b.sc.Connect()
}

type pickerWrapper struct {
	mu sync.Mutex
}

type acBalancerWrapper struct {
	mu sync.Mutex
	ac *addrConn
}

type addrConn struct {
	cc   *ClientConn
	acbw SubConn
	mu   sync.Mutex
}

func (ac *addrConn) resetTransport() {
	_ = minConnectTimeout
}

func (ac *addrConn) transportMonitor() {
	ac.resetTransport()
}

func (ac *addrConn) connect() {
	go func() {
		ac.transportMonitor()
	}()
}

func (acbw *acBalancerWrapper) Connect() {
	acbw.mu.Lock()
	defer acbw.mu.Unlock()
	acbw.ac.connect()
}

func newPickerWrapper() *pickerWrapper {
	return &pickerWrapper{}
}

type ClientConn struct {
	mu sync.Mutex
}

func (cc *ClientConn) switchBalancer() {
	builder := newPickfirstBuilder()
	newCCBalancerWrapper(cc, builder)
}

func (cc *ClientConn) newAddrConn() *addrConn {
	return &addrConn{cc: cc}
}

type ccBalancerWrapper struct {
	cc       *ClientConn
	balancer Balancer
}

func (ccb *ccBalancerWrapper) watcher() {
	for i := 0; i < 10; i++ {
		balanceMutex.Lock()
		if ccb.balancer != nil {
			balanceMutex.Unlock()
			ccb.balancer.HandleResolvedAddrs()
		} else {
			balanceMutex.Unlock()
		}
	}
}

func (ccb *ccBalancerWrapper) NewSubConn() SubConn {
	ac := ccb.cc.newAddrConn()
	acbw := &acBalancerWrapper{ac: ac}
	acbw.ac.mu.Lock()
	ac.acbw = acbw
	acbw.ac.mu.Unlock()
	return acbw
}

func newCCBalancerWrapper(cc *ClientConn, b Builder) {
	ccb := &ccBalancerWrapper{cc: cc}
	go ccb.watcher()
	balanceMutex.Lock()
	defer balanceMutex.Unlock()
	ccb.balancer = b.Build(ccb)
}

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

	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		mctBkp := minConnectTimeout
		// Call this only after transportMonitor goroutine has ended.
		defer func() {
			minConnectTimeout = mctBkp
		}()
		cc := &ClientConn{}
		cc.switchBalancer()
	}()
	wg.Wait()
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14762383879680,
    "event_type": "GoCreate",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14762383886720,
    "event_type": "GoCreate",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14762383888704,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14762383899456,
    "event_type": "GoCreate",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14762383899776,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14762383899776,
  "event_type": "GoStart",
  "goroutine_id": 8,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: race
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel grpc_1748 (race)

package main

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

var minConnectTimeout = 10 * time.Second

var balanceMutex sync.Mutex // We add this for avoiding other data race

type Balancer interface {
	HandleResolvedAddrs()
}

type Builder interface {
	Build(cc balancer_ClientConn) Balancer
}

func newPickfirstBuilder() Builder {
	return &pickfirstBuilder{}
}

type pickfirstBuilder struct{}

func (*pickfirstBuilder) Build(cc balancer_ClientConn) Balancer {
	return &pickfirstBalancer{cc: cc}
}

type SubConn interface {
	Connect()
}

type balancer_ClientConn interface {
	NewSubConn() SubConn
}

type pickfirstBalancer struct {
	cc balancer_ClientConn
	sc SubConn
}

func (b *pickfirstBalancer) HandleResolvedAddrs() {
	b.sc = b.cc.NewSubConn()
	b.sc.Connect()
}

type pickerWrapper struct {
	mu sync.Mutex
}

type acBalancerWrapper struct {
	mu sync.Mutex
	ac *addrConn
}

type addrConn struct {
	cc   *ClientConn
	acbw SubConn
	mu   sync.Mutex
}

func (ac *addrConn) resetTransport() {
	_ = minConnectTimeout
}

func (ac *addrConn) transportMonitor() {
	ac.resetTransport()
}

func (ac *addrConn) connect() {
	go func() {
		ac.transportMonitor()
	}()
}

func (acbw *acBalancerWrapper) Connect() {
	acbw.mu.Lock()
	defer acbw.mu.Unlock()
	acbw.ac.connect()
}

func newPickerWrapper() *pickerWrapper {
	return &pickerWrapper{}
}

type ClientConn struct {
	mu sync.Mutex
}

func (cc *ClientConn) switchBalancer() {
	builder := newPickfirstBuilder()
	newCCBalancerWrapper(cc, builder)
}

func (cc *ClientConn) newAddrConn() *addrConn {
	return &addrConn{cc: cc}
}

type ccBalancerWrapper struct {
	cc       *ClientConn
	balancer Balancer
}

func (ccb *ccBalancerWrapper) watcher() {
	for i := 0; i < 10; i++ {
		balanceMutex.Lock()
		if ccb.balancer != nil {
			balanceMutex.Unlock()
			ccb.balancer.HandleResolvedAddrs()
		} else {
			balanceMutex.Unlock()
		}
	}
}

func (ccb *ccBalancerWrapper) NewSubConn() SubConn {
	ac := ccb.cc.newAddrConn()
	acbw := &acBalancerWrapper{ac: ac}
	acbw.ac.mu.Lock()
	ac.acbw = acbw
	acbw.ac.mu.Unlock()
	return acbw
}

func newCCBalancerWrapper(cc *ClientConn, b Builder) {
	ccb := &ccBalancerWrapper{cc: cc}
	go ccb.watcher()
	balanceMutex.Lock()
	defer balanceMutex.Unlock()
	ccb.balancer = b.Build(ccb)
}

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

	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		mctBkp := minConnectTimeout
		// Call this only after transportMonitor goroutine has ended.
		defer func() {
			minConnectTimeout = mctBkp
		}()
		cc := &ClientConn{}
		cc.switchBalancer()
	}()
	wg.Wait()
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14762383879680,
    "event_type": "GoCreate",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14762383886720,
    "event_type": "GoCreate",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14762383888704,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14762383899456,
    "event_type": "GoCreate",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14762383899776,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14762383899776,
  "event_type": "GoStart",
  "goroutine_id": 8,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoStart", "goroutine_id": 36}


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: race
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel grpc_1748 (race)

package main

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

var minConnectTimeout = 10 * time.Second

var balanceMutex sync.Mutex // We add this for avoiding other data race

type Balancer interface {
	HandleResolvedAddrs()
}

type Builder interface {
	Build(cc balancer_ClientConn) Balancer
}

func newPickfirstBuilder() Builder {
	return &pickfirstBuilder{}
}

type pickfirstBuilder struct{}

func (*pickfirstBuilder) Build(cc balancer_ClientConn) Balancer {
	return &pickfirstBalancer{cc: cc}
}

type SubConn interface {
	Connect()
}

type balancer_ClientConn interface {
	NewSubConn() SubConn
}

type pickfirstBalancer struct {
	cc balancer_ClientConn
	sc SubConn
}

func (b *pickfirstBalancer) HandleResolvedAddrs() {
	b.sc = b.cc.NewSubConn()
	b.sc.Connect()
}

type pickerWrapper struct {
	mu sync.Mutex
}

type acBalancerWrapper struct {
	mu sync.Mutex
	ac *addrConn
}

type addrConn struct {
	cc   *ClientConn
	acbw SubConn
	mu   sync.Mutex
}

func (ac *addrConn) resetTransport() {
	_ = minConnectTimeout
}

func (ac *addrConn) transportMonitor() {
	ac.resetTransport()
}

func (ac *addrConn) connect() {
	go func() {
		ac.transportMonitor()
	}()
}

func (acbw *acBalancerWrapper) Connect() {
	acbw.mu.Lock()
	defer acbw.mu.Unlock()
	acbw.ac.connect()
}

func newPickerWrapper() *pickerWrapper {
	return &pickerWrapper{}
}

type ClientConn struct {
	mu sync.Mutex
}

func (cc *ClientConn) switchBalancer() {
	builder := newPickfirstBuilder()
	newCCBalancerWrapper(cc, builder)
}

func (cc *ClientConn) newAddrConn() *addrConn {
	return &addrConn{cc: cc}
}

type ccBalancerWrapper struct {
	cc       *ClientConn
	balancer Balancer
}

func (ccb *ccBalancerWrapper) watcher() {
	for i := 0; i < 10; i++ {
		balanceMutex.Lock()
		if ccb.balancer != nil {
			balanceMutex.Unlock()
			ccb.balancer.HandleResolvedAddrs()
		} else {
			balanceMutex.Unlock()
		}
	}
}

func (ccb *ccBalancerWrapper) NewSubConn() SubConn {
	ac := ccb.cc.newAddrConn()
	acbw := &acBalancerWrapper{ac: ac}
	acbw.ac.mu.Lock()
	ac.acbw = acbw
	acbw.ac.mu.Unlock()
	return acbw
}

func newCCBalancerWrapper(cc *ClientConn, b Builder) {
	ccb := &ccBalancerWrapper{cc: cc}
	go ccb.watcher()
	balanceMutex.Lock()
	defer balanceMutex.Unlock()
	ccb.balancer = b.Build(ccb)
}

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

	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		mctBkp := minConnectTimeout
		// Call this only after transportMonitor goroutine has ended.
		defer func() {
			minConnectTimeout = mctBkp
		}()
		cc := &ClientConn{}
		cc.switchBalancer()
	}()
	wg.Wait()
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14762383879680,
    "event_type": "GoCreate",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14762383886720,
    "event_type": "GoCreate",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14762383888704,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14762383899456,
    "event_type": "GoCreate",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14762383899776,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14762383899776,
  "event_type": "GoStart",
  "goroutine_id": 8,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

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


[System] You are a code execution simulator.

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

Here is a Go program:
<program>
// WEAVE_META
// outcome: race
// concurrency_pattern: mutex
// goroutine_count: 3
// expected_nondeterminism: medium
// description: Human-written GoBench bug kernel grpc_1748 (race)

package main

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

var minConnectTimeout = 10 * time.Second

var balanceMutex sync.Mutex // We add this for avoiding other data race

type Balancer interface {
	HandleResolvedAddrs()
}

type Builder interface {
	Build(cc balancer_ClientConn) Balancer
}

func newPickfirstBuilder() Builder {
	return &pickfirstBuilder{}
}

type pickfirstBuilder struct{}

func (*pickfirstBuilder) Build(cc balancer_ClientConn) Balancer {
	return &pickfirstBalancer{cc: cc}
}

type SubConn interface {
	Connect()
}

type balancer_ClientConn interface {
	NewSubConn() SubConn
}

type pickfirstBalancer struct {
	cc balancer_ClientConn
	sc SubConn
}

func (b *pickfirstBalancer) HandleResolvedAddrs() {
	b.sc = b.cc.NewSubConn()
	b.sc.Connect()
}

type pickerWrapper struct {
	mu sync.Mutex
}

type acBalancerWrapper struct {
	mu sync.Mutex
	ac *addrConn
}

type addrConn struct {
	cc   *ClientConn
	acbw SubConn
	mu   sync.Mutex
}

func (ac *addrConn) resetTransport() {
	_ = minConnectTimeout
}

func (ac *addrConn) transportMonitor() {
	ac.resetTransport()
}

func (ac *addrConn) connect() {
	go func() {
		ac.transportMonitor()
	}()
}

func (acbw *acBalancerWrapper) Connect() {
	acbw.mu.Lock()
	defer acbw.mu.Unlock()
	acbw.ac.connect()
}

func newPickerWrapper() *pickerWrapper {
	return &pickerWrapper{}
}

type ClientConn struct {
	mu sync.Mutex
}

func (cc *ClientConn) switchBalancer() {
	builder := newPickfirstBuilder()
	newCCBalancerWrapper(cc, builder)
}

func (cc *ClientConn) newAddrConn() *addrConn {
	return &addrConn{cc: cc}
}

type ccBalancerWrapper struct {
	cc       *ClientConn
	balancer Balancer
}

func (ccb *ccBalancerWrapper) watcher() {
	for i := 0; i < 10; i++ {
		balanceMutex.Lock()
		if ccb.balancer != nil {
			balanceMutex.Unlock()
			ccb.balancer.HandleResolvedAddrs()
		} else {
			balanceMutex.Unlock()
		}
	}
}

func (ccb *ccBalancerWrapper) NewSubConn() SubConn {
	ac := ccb.cc.newAddrConn()
	acbw := &acBalancerWrapper{ac: ac}
	acbw.ac.mu.Lock()
	ac.acbw = acbw
	acbw.ac.mu.Unlock()
	return acbw
}

func newCCBalancerWrapper(cc *ClientConn, b Builder) {
	ccb := &ccBalancerWrapper{cc: cc}
	go ccb.watcher()
	balanceMutex.Lock()
	defer balanceMutex.Unlock()
	ccb.balancer = b.Build(ccb)
}

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

	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		mctBkp := minConnectTimeout
		// Call this only after transportMonitor goroutine has ended.
		defer func() {
			minConnectTimeout = mctBkp
		}()
		cc := &ClientConn{}
		cc.switchBalancer()
	}()
	wg.Wait()
}

</program>

Here is a partial execution trace showing goroutine scheduler events so far:
<trace>
[
  {
    "event_id": 0,
    "timestamp_ns": 14762383879680,
    "event_type": "GoCreate",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 1,
    "timestamp_ns": 14762383886720,
    "event_type": "GoCreate",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.traceStartReadCPU"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 2,
    "timestamp_ns": 14762383888704,
    "event_type": "GoStart",
    "goroutine_id": 7,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 3,
    "timestamp_ns": 14762383899456,
    "event_type": "GoCreate",
    "goroutine_id": 9,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime.(*traceAdvancerState).start"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  },
  {
    "event_id": 4,
    "timestamp_ns": 14762383899776,
    "event_type": "GoStart",
    "goroutine_id": 8,
    "goroutines": {
      "1": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "7": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "8": {
        "status": "running",
        "blocked_on": null,
        "locals_hint": "unknown"
      },
      "9": {
        "status": "runnable",
        "blocked_on": null,
        "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
      }
    },
    "channels": {},
    "mutexes": {}
  }
]
</trace>

The current goroutine states are:
<current_state>
{
  "event_id": 4,
  "timestamp_ns": 14762383899776,
  "event_type": "GoStart",
  "goroutine_id": 8,
  "goroutines": {
    "1": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "7": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "8": {
      "status": "running",
      "blocked_on": null,
      "locals_hint": "unknown"
    },
    "9": {
      "status": "runnable",
      "blocked_on": null,
      "locals_hint": "runtime/trace.(*traceMultiplexer).startLocked"
    }
  },
  "channels": {},
  "mutexes": {}
}
</current_state>

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

[Assistant] {"event_type": "GoStart", "goroutine_id": 38}