// allocation.
	if newsize < fixedStack {
		return
	}
	// Compute how much of the stack is currently in use and only
	// shrink the stack if gp is using less than a quarter of its
	// current stack. The currently used stack includes everything
	// down to the SP plus the stack guard space that ensures
	// there's room for nosplit functions.
	avail := gp.stack.hi - gp.stack.lo

	EvUserTaskEnd     // end of a task [timestamp, internal task ID, stack ID]
	EvUserRegionBegin // trace.{Start,With}Region [timestamp, internal task ID, name string ID, stack ID]
	EvUserRegionEnd   // trace.{End,With}Region [timestamp, internal task ID, name string ID, stack ID]
	EvUserLog         // trace.Log [timestamp, internal task ID, key string ID, value string ID, stack]

	// Coroutines. Added in Go 1.23.

	b10.Event("GoStop", "whatever", testgen.NoStack)

	// The running goroutine gets unblocked.
	b11 := g1.Batch(trace.ThreadID(1), 0)
	b11.Event("ProcStatus", trace.ProcID(1), go122.ProcRunning)
	b11.Event("GoStart", trace.GoID(1), testgen.Seq(1))
	b11.Event("GoStop", "whatever", testgen.NoStack)

	g2 := t.Generation(2)

	// Start running the goroutine, but later.

func (gs *gState[R]) setStartCause(ts trace.Time, name string, resource uint64, stack trace.Stack) {
	gs.startCause.time = ts
	gs.startCause.name = name
	gs.startCause.resource = resource
	gs.startCause.stack = stack
}

// created indicates that this goroutine was just created by the provided creator.
func (gs *gState[R]) created(ts trace.Time, creator R, stack trace.Stack) {
	if creator == R(noResource) {
		return
	}

)

// PrintStack prints to standard error the stack trace returned by runtime.Stack.
func PrintStack() {
	os.Stderr.Write(Stack())
}

// Stack returns a formatted stack trace of the goroutine that calls it.
// It calls [runtime.Stack] with a large enough buffer to capture the entire trace.
func Stack() []byte {
	buf := make([]byte, 1024)
	for {
		n := runtime.Stack(buf, false)
		if n < len(buf) {
			return buf[:n]
		}

	g.strings[s] = id
	return id
}

// Stack registers a stack with the trace.
//
// This is a convenience function for easily adding correct
// stacks to traces.
func (g *Generation) Stack(stk []trace.StackFrame) uint64 {
	if len(stk) == 0 {
		return 0
	}
	if len(stk) > 32 {
		panic("stack too big for test")
	}
	var stkc stack
	copy(stkc.stk[:], stk)
	stkc.len = len(stk)

	g2 := t.Generation(2)

	// That same goroutine emits a task end in the following generation.
	b2 := g2.Batch(trace.ThreadID(0), 5)
	b2.Event("ProcStatus", trace.ProcID(0), go122.ProcRunning)
	b2.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunning)
	b2.Event("UserTaskEnd", trace.TaskID(2), testgen.NoStack)

	b0.Event("ProcStatus", trace.ProcID(0), go122.ProcRunning)
	b0.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunning)
	b0.Event("GoSyscallBegin", testgen.Seq(1), testgen.NoStack)
	b0.Event("GoSyscallEnd")
	b0.Event("GoSyscallBegin", testgen.Seq(2), testgen.NoStack)
	b0.Event("GoSyscallEndBlocked")

	// A running goroutine steals proc 0.
	b1 := g.Batch(trace.ThreadID(1), 0)
	b1.Event("ProcStatus", trace.ProcID(2), go122.ProcRunning)

	b0 := g.Batch(trace.ThreadID(0), 0)
	b0.Event("ProcStatus", trace.ProcID(0), go122.ProcRunning)
	b0.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunning)
	b0.Event("GoSyscallBegin", testgen.Seq(1), testgen.NoStack)
	b0.Event("GoSyscallEndBlocked")

	// A running goroutine steals proc 0.
	b1 := g.Batch(trace.ThreadID(1), 0)
	b1.Event("ProcStatus", trace.ProcID(2), go122.ProcRunning)

	//
	// An event may not be both a timed event and have data.
	HasData bool

	// IsStack indicates that the event represents a complete
	// stack trace. Specifically, it means that after the arguments
	// there's a varint length, followed by 4*length varints. Each
	// group of 4 represents the PC, file ID, func ID, and line number
	// in that order.
	IsStack bool

	// Experiment indicates the ID of an experiment this event is associated