diff --git a/cmd/qrunproxy/main.go b/cmd/qrunproxy/main.go
index 0d5a67c..c49e181 100644
--- a/cmd/qrunproxy/main.go
+++ b/cmd/qrunproxy/main.go
@@ -28,7 +28,7 @@ func main() {
 		runAndExit = strings.Fields(*runAndExitStr)
 	}
 
-	show := GenerateMockShow(7, 100, 1000)
+	show := GenerateMockShow(5, 100, 1000)
 	if err := show.Validate(); err != nil {
 		fmt.Fprintf(os.Stderr, "Error validating show: %v\n", err)
 		os.Exit(1)
diff --git a/cmd/qrunproxy/mockshow.go b/cmd/qrunproxy/mockshow.go
index 0fc371f..4c6f7ad 100644
--- a/cmd/qrunproxy/mockshow.go
+++ b/cmd/qrunproxy/mockshow.go
@@ -1,70 +1,144 @@
 package main
 
-import "fmt"
+import (
+	"fmt"
+	"math/rand/v2"
+)
+
+var trackNamePool = []string{
+	"Lighting", "Fill Light", "Spots", "Video", "Video OVL",
+	"Audio", "SFX", "Ambience", "Pyro", "Fog", "Motors",
+	"Follow Spot", "Haze", "Projector", "LED Wall",
+}
+
+var lightNamePool = []string{
+	"Wash", "Focus", "Spot", "Amber", "Blue", "Cool", "Warm",
+	"Flood", "Strobe", "Blackout", "Dim", "Bright", "Sunrise",
+}
+
+var mediaNamePool = []string{
+	"Loop", "Projection", "Background", "Overlay", "Flash",
+	"Ambience", "Underscore", "Sting", "Bumper", "Transition",
+}
+
+var delayNamePool = []string{
+	"1s Delay", "2s Delay", "3s Delay", "5s Delay", "Hold",
+}
 
 func GenerateMockShow(numTracks, numCues, numBlocks int) *Show {
-	show := &Show{}
+	rng := rand.New(rand.NewPCG(42, 0))
 
+	show := &Show{}
+	blockIdx := 0
+	nextBlockID := func() string {
+		id := fmt.Sprintf("b%d", blockIdx)
+		blockIdx++
+		return id
+	}
+
+	names := make([]string, len(trackNamePool))
+	copy(names, trackNamePool)
+	rng.Shuffle(len(names), func(i, j int) {
+		names[i], names[j] = names[j], names[i]
+	})
 	for i := range numTracks {
+		name := names[i%len(names)]
+		if i >= len(names) {
+			name = fmt.Sprintf("%s %d", name, i/len(names)+1)
+		}
 		show.Tracks = append(show.Tracks, &Track{
 			ID:   fmt.Sprintf("track_%d", i),
-			Name: fmt.Sprintf("Track %d", i),
+			Name: name,
 		})
 	}
 
-	for i := range numCues {
-		show.Blocks = append(show.Blocks, &Block{
-			ID:   fmt.Sprintf("cue_%d", i),
+	randBlock := func(trackIdx int) *Block {
+		r := rng.Float64()
+		var typ, name string
+		var loop bool
+		switch {
+		case r < 0.30:
+			typ, name = "light", lightNamePool[rng.IntN(len(lightNamePool))]
+		case r < 0.55:
+			typ, name = "media", mediaNamePool[rng.IntN(len(mediaNamePool))]
+		case r < 0.70:
+			typ, name, loop = "media", mediaNamePool[rng.IntN(len(mediaNamePool))], true
+		case r < 0.80:
+			typ, name = "delay", delayNamePool[rng.IntN(len(delayNamePool))]
+		default:
+			typ, name = "light", lightNamePool[rng.IntN(len(lightNamePool))]
+		}
+		return &Block{
+			ID:    nextBlockID(),
+			Type:  typ,
+			Track: fmt.Sprintf("track_%d", trackIdx),
+			Name:  name,
+			Loop:  loop,
+		}
+	}
+
+	placed := 0
+	cueIdx := 0
+
+	for placed < numBlocks && cueIdx < numCues {
+		cue := &Block{
+			ID:   fmt.Sprintf("q%d", cueIdx*10),
 			Type: "cue",
-			Name: fmt.Sprintf("Cue %d", i),
-		})
-	}
-
-	blocksByTrack := make([][]*Block, numTracks)
-	for i := range numBlocks {
-		trackIdx := i % numTracks
-		trackID := fmt.Sprintf("track_%d", trackIdx)
-		block := &Block{
-			ID:    fmt.Sprintf("block_%d_%d", trackIdx, len(blocksByTrack[trackIdx])),
-			Type:  "media",
-			Track: trackID,
-			Name:  fmt.Sprintf("Block %d-%d", trackIdx, len(blocksByTrack[trackIdx])),
+			Name: fmt.Sprintf("Q%d", cueIdx*10),
 		}
-		show.Blocks = append(show.Blocks, block)
-		blocksByTrack[trackIdx] = append(blocksByTrack[trackIdx], block)
-	}
+		show.Blocks = append(show.Blocks, cue)
+		cueIdx++
 
-	for trackIdx := range numTracks {
-		blocks := blocksByTrack[trackIdx]
-		for i := 1; i < len(blocks); i++ {
-			show.Triggers = append(show.Triggers, &Trigger{
-				Source:  TriggerSource{Block: blocks[i-1].ID, Signal: "END"},
-				Targets: []TriggerTarget{{Block: blocks[i].ID, Hook: "START"}},
-			})
-		}
-	}
+		tracksThisCue := numTracks - rng.IntN(2)
+		perm := rng.Perm(numTracks)
 
-	headPerTrack := make([]int, numTracks)
-	for i := range numCues {
-		cue := show.Blocks[i]
-		targets := []TriggerTarget{}
-		for trackIdx := range numTracks {
-			if headPerTrack[trackIdx] >= len(blocksByTrack[trackIdx]) {
-				continue
+		cueTargets := []TriggerTarget{}
+		for _, trackIdx := range perm[:tracksThisCue] {
+			if placed >= numBlocks {
+				break
+			}
+			block := randBlock(trackIdx)
+			show.Blocks = append(show.Blocks, block)
+			cueTargets = append(cueTargets, TriggerTarget{Block: block.ID, Hook: "START"})
+			placed++
+
+			prev := block
+			chainLen := rng.IntN(3)
+			for range chainLen {
+				if placed >= numBlocks {
+					break
+				}
+				if !prev.hasDefinedTiming() {
+					break
+				}
+				next := randBlock(trackIdx)
+				show.Blocks = append(show.Blocks, next)
+				show.Triggers = append(show.Triggers, &Trigger{
+					Source:  TriggerSource{Block: prev.ID, Signal: "END"},
+					Targets: []TriggerTarget{{Block: next.ID, Hook: "START"}},
+				})
+				prev = next
+				placed++
 			}
-			block := blocksByTrack[trackIdx][headPerTrack[trackIdx]]
-			targets = append(targets, TriggerTarget{Block: block.ID, Hook: "START"})
-			depth := len(blocksByTrack[trackIdx]) - headPerTrack[trackIdx]
-			advance := max(depth/(numCues-i), 1)
-			headPerTrack[trackIdx] += advance
 		}
-		if len(targets) > 0 {
+
+		if len(cueTargets) > 0 {
 			show.Triggers = append(show.Triggers, &Trigger{
 				Source:  TriggerSource{Block: cue.ID, Signal: "GO"},
-				Targets: targets,
+				Targets: cueTargets,
 			})
 		}
 	}
 
+	for cueIdx < numCues {
+		cue := &Block{
+			ID:   fmt.Sprintf("q%d", cueIdx*10),
+			Type: "cue",
+			Name: fmt.Sprintf("Q%d", cueIdx*10),
+		}
+		show.Blocks = append(show.Blocks, cue)
+		cueIdx++
+	}
+
 	return show
 }
diff --git a/cmd/qrunproxy/show.go b/cmd/qrunproxy/show.go
index fff814f..9d5ddd1 100644
--- a/cmd/qrunproxy/show.go
+++ b/cmd/qrunproxy/show.go
@@ -36,6 +36,16 @@ type TriggerTarget struct {
 	Hook  string `json:"hook"`
 }
 
+func (block *Block) hasDefinedTiming() bool {
+	if block.Type == "cue" || block.Type == "delay" {
+		return true
+	}
+	if block.Type == "media" && !block.Loop {
+		return true
+	}
+	return false
+}
+
 func isValidEventForBlock(block *Block, event string) bool {
 	if block.Type == "cue" {
 		return event == "GO"
@@ -75,6 +85,11 @@ func (show *Show) Validate() error {
 		}
 	}
 
+	type blockEvent struct {
+		block string
+		event string
+	}
+	hookTargeted := map[blockEvent]bool{}
 	startTargeted := map[string]bool{}
 	for _, trigger := range show.Triggers {
 		sourceBlock := blocksByID[trigger.Source.Block]
@@ -93,6 +108,7 @@ func (show *Show) Validate() error {
 			if !isValidEventForBlock(targetBlock, target.Hook) {
 				return fmt.Errorf("trigger target hook %q is invalid for block %q", target.Hook, target.Block)
 			}
+			hookTargeted[blockEvent{target.Block, target.Hook}] = true
 			if target.Hook == "START" {
 				startTargeted[target.Block] = true
 			}
@@ -108,5 +124,28 @@ func (show *Show) Validate() error {
 		}
 	}
 
+	for _, trigger := range show.Triggers {
+		sourceBlock := blocksByID[trigger.Source.Block]
+		for _, target := range trigger.Targets {
+			targetBlock := blocksByID[target.Block]
+			if sourceBlock.Type != "cue" && targetBlock.Type != "cue" && sourceBlock.Track == targetBlock.Track && target.Hook == "START" && trigger.Source.Signal != "END" {
+				return fmt.Errorf("same-track START trigger from %q to %q must use END signal, not %s", sourceBlock.ID, targetBlock.ID, trigger.Source.Signal)
+			}
+		}
+		if sourceBlock.hasDefinedTiming() {
+			continue
+		}
+		signal := trigger.Source.Signal
+		if signal != "FADE_OUT" && signal != "END" {
+			continue
+		}
+		if signal == "END" && hookTargeted[blockEvent{sourceBlock.ID, "FADE_OUT"}] {
+			continue
+		}
+		if !hookTargeted[blockEvent{sourceBlock.ID, signal}] {
+			return fmt.Errorf("block %q has no defined timing and nothing triggers its %s, so its %s signal will never fire", sourceBlock.ID, signal, signal)
+		}
+	}
+
 	return nil
 }
diff --git a/cmd/qrunproxy/static/index.html b/cmd/qrunproxy/static/index.html
index 63f134f..baaf093 100644
--- a/cmd/qrunproxy/static/index.html
+++ b/cmd/qrunproxy/static/index.html
@@ -186,7 +186,8 @@ function render(data) {
       div.className = 'cell' + rowCls;
       if (c.is_title) {
         const block = data.blocks[c.block_id] || {};
-        div.innerHTML = `<div class="block block-mid ${block.type || ''}"><div class="title">${block.name || ''}</div></div>`;
+        const loop = block.loop ? ' \u21A9' : '';
+        div.innerHTML = `<div class="block block-mid ${block.type || ''}"><div class="title">${block.name || ''}${loop}</div></div>`;
       } else if (c.block_id) {
         const block = data.blocks[c.block_id] || {};
         const isInfinity = r === numRows - 1 && !c.is_end && !c.is_title;
diff --git a/cmd/qrunproxy/timeline.go b/cmd/qrunproxy/timeline.go
index a193d81..02f94f0 100644
--- a/cmd/qrunproxy/timeline.go
+++ b/cmd/qrunproxy/timeline.go
@@ -1,5 +1,7 @@
 package main
 
+import "fmt"
+
 const cueTrackID = "_cue"
 
 type TimelineTrack struct {
@@ -84,7 +86,9 @@ func BuildTimeline(show *Show) (Timeline, error) {
 
 	tl.buildCells(endChains)
 	tl.buildConstraints()
-	tl.assignRows()
+	if err := tl.assignRows(); err != nil {
+		return Timeline{}, err
+	}
 
 	return tl, nil
 }
@@ -174,16 +178,29 @@ func (tl *Timeline) buildConstraints() {
 	}
 }
 
-func (tl *Timeline) assignRows() {
-	for {
+func (tl *Timeline) assignRows() error {
+	for range 1000000 {
 		if tl.enforceConstraints() {
 			continue
 		}
 		if tl.enforceExclusives() {
 			continue
 		}
-		break
+		return nil
 	}
+	for _, c := range tl.constraints {
+		switch c.kind {
+		case "same_row":
+			if c.a.row != c.b.row {
+				return fmt.Errorf("assignRows: unsatisfied %s constraint: %s/%s (row %d) vs %s/%s (row %d)", c.kind, c.a.BlockID, c.a.Event, c.a.row, c.b.BlockID, c.b.Event, c.b.row)
+			}
+		case "next_row":
+			if c.b.row <= c.a.row {
+				return fmt.Errorf("assignRows: unsatisfied %s constraint: %s/%s (row %d) must follow %s/%s (row %d)", c.kind, c.b.BlockID, c.b.Event, c.b.row, c.a.BlockID, c.a.Event, c.a.row)
+			}
+		}
+	}
+	return fmt.Errorf("assignRows: did not converge")
 }
 
 func (tl *Timeline) enforceConstraints() bool {
diff --git a/cmd/qrunproxy/timeline_test.go b/cmd/qrunproxy/timeline_test.go
index 9ae80f5..fb5fca6 100644
--- a/cmd/qrunproxy/timeline_test.go
+++ b/cmd/qrunproxy/timeline_test.go
@@ -1,26 +1,32 @@
 package main
 
-import "testing"
+import (
+	"testing"
+	"time"
+)
 
 func TestBuildTimelineFromMockShow(t *testing.T) {
-	show := GenerateMockShow(7, 100, 1000)
+	t0 := time.Now()
+	show := GenerateMockShow(5, 100, 1000)
+	t.Logf("GenerateMockShow: %v (%d blocks, %d triggers)", time.Since(t0), len(show.Blocks), len(show.Triggers))
+
+	t1 := time.Now()
 	if err := show.Validate(); err != nil {
 		t.Fatalf("generated show failed validation: %v", err)
 	}
+	t.Logf("Validate: %v", time.Since(t1))
+
+	t2 := time.Now()
 	tl, err := BuildTimeline(show)
+	t.Logf("BuildTimeline: %v", time.Since(t2))
 	if err != nil {
 		t.Fatalf("BuildTimeline failed: %v", err)
 	}
-	if len(tl.Tracks) != 8 {
-		t.Errorf("expected 8 tracks (7 + cue), got %d", len(tl.Tracks))
-	}
-	if len(tl.Blocks) != 1100 {
-		t.Errorf("expected 1100 blocks (100 cues + 1000), got %d", len(tl.Blocks))
-	}
+	t.Logf("tracks=%d blocks=%d", len(tl.Tracks), len(tl.Blocks))
 }
 
 func BenchmarkBuildTimeline(b *testing.B) {
-	show := GenerateMockShow(7, 100, 1000)
+	show := GenerateMockShow(5, 100, 1000)
 	if err := show.Validate(); err != nil {
 		b.Fatal(err)
 	}