feat: add a dependency management graph for agents (#20208)

Relates to https://github.com/coder/internal/issues/1093

This is the first of N pull requests to allow coder script ordering.
It introduces what is for now dead code, but paves the way for various
interfaces that allow coder scripts and other processes to depend on one
another via CLI commands and terraform configurations.

The next step is to add reactivity to the graph, such that changes in
the status of one vertex will propagate and allow other vertices to
change their own statuses.

Concurrency and stress testing yield the following:

CPU Profile:
<img width="1512" height="862" alt="Screenshot 2025-10-17 at 10 38 52"
src="https://github.com/user-attachments/assets/f46cf1a2-a0b2-4c02-81a0-069798108ee5"
/>

Mem Profile:
<img width="1512" height="862" alt="Screenshot 2025-10-17 at 10 38 01"
src="https://github.com/user-attachments/assets/45be1235-fff6-45ba-a50d-db9880377bd0"
/>

Predictably, lock contention and memory allocation are the largest
components of this system under stress. Nothing seems untoward.

.gitignore

@@ -12,6 +12,9 @@ node_modules/
 vendor/
 yarn-error.log
 
+# Test output files
+test-output/
+
 # VSCode settings.
 **/.vscode/*
 # Allow VSCode recommendations and default settings in project root.

Makefile

@@ -676,6 +676,7 @@ gen/db: $(DB_GEN_FILES)
 .PHONY: gen/db
 
 gen/golden-files: \
+	agent/unit/testdata/.gen-golden \
 	cli/testdata/.gen-golden \
 	coderd/.gen-golden \
 	coderd/notifications/.gen-golden \
@@ -952,6 +953,10 @@ clean/golden-files:
 		-type f -name '*.golden' -delete
 .PHONY: clean/golden-files
 
+agent/unit/testdata/.gen-golden: $(wildcard agent/unit/testdata/*.golden) $(GO_SRC_FILES) $(wildcard agent/unit/*_test.go)
+	TZ=UTC go test ./agent/unit -run="TestGraph" -update
+	touch "$@"
+
 cli/testdata/.gen-golden: $(wildcard cli/testdata/*.golden) $(wildcard cli/*.tpl) $(GO_SRC_FILES) $(wildcard cli/*_test.go)
 	TZ=UTC go test ./cli -run="Test(CommandHelp|ServerYAML|ErrorExamples|.*Golden)" -update
 	touch "$@"

agent/unit/graph.go

@@ -0,0 +1,174 @@
+package unit
+
+import (
+	"fmt"
+	"sync"
+
+	"golang.org/x/xerrors"
+	"gonum.org/v1/gonum/graph/encoding/dot"
+	"gonum.org/v1/gonum/graph/simple"
+	"gonum.org/v1/gonum/graph/topo"
+)
+
+// Graph provides a bidirectional interface over gonum's directed graph implementation.
+// While the underlying gonum graph is directed, we overlay bidirectional semantics
+// by distinguishing between forward and reverse edges. Wanting and being wanted by
+// other units are related but different concepts that have different graph traversal
+// implications when Units update their status.
+//
+// The graph stores edge types to represent different relationships between units,
+// allowing for domain-specific semantics beyond simple connectivity.
+type Graph[EdgeType, VertexType comparable] struct {
+	mu sync.RWMutex
+	// The underlying gonum graph. It stores vertices and edges without knowing about the types of the vertices and edges.
+	gonumGraph *simple.DirectedGraph
+	// Maps vertices to their IDs so that a gonum vertex ID can be used to lookup the vertex type.
+	vertexToID map[VertexType]int64
+	// Maps vertex IDs to their types so that a vertex type can be used to lookup the gonum vertex ID.
+	idToVertex map[int64]VertexType
+	// The next ID to assign to a vertex.
+	nextID int64
+	// Store edge types by "fromID->toID" key. This is used to lookup the edge type for a given edge.
+	edgeTypes map[string]EdgeType
+}
+
+// Edge is a convenience type for representing an edge in the graph.
+// It encapsulates the from and to vertices and the edge type itself.
+type Edge[EdgeType, VertexType comparable] struct {
+	From VertexType
+	To   VertexType
+	Edge EdgeType
+}
+
+// AddEdge adds an edge to the graph. It initializes the graph and metadata on first use,
+// checks for cycles, and adds the edge to the gonum graph.
+func (g *Graph[EdgeType, VertexType]) AddEdge(from, to VertexType, edge EdgeType) error {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
+	if g.gonumGraph == nil {
+		g.gonumGraph = simple.NewDirectedGraph()
+		g.vertexToID = make(map[VertexType]int64)
+		g.idToVertex = make(map[int64]VertexType)
+		g.edgeTypes = make(map[string]EdgeType)
+		g.nextID = 1
+	}
+
+	fromID := g.getOrCreateVertexID(from)
+	toID := g.getOrCreateVertexID(to)
+
+	if g.canReach(to, from) {
+		return xerrors.Errorf("adding edge (%v -> %v) would create a cycle", from, to)
+	}
+
+	g.gonumGraph.SetEdge(simple.Edge{F: simple.Node(fromID), T: simple.Node(toID)})
+
+	edgeKey := fmt.Sprintf("%d->%d", fromID, toID)
+	g.edgeTypes[edgeKey] = edge
+
+	return nil
+}
+
+// GetForwardAdjacentVertices returns all the edges that originate from the given vertex.
+func (g *Graph[EdgeType, VertexType]) GetForwardAdjacentVertices(from VertexType) []Edge[EdgeType, VertexType] {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	fromID, exists := g.vertexToID[from]
+	if !exists {
+		return []Edge[EdgeType, VertexType]{}
+	}
+
+	edges := []Edge[EdgeType, VertexType]{}
+	toNodes := g.gonumGraph.From(fromID)
+	for toNodes.Next() {
+		toID := toNodes.Node().ID()
+		to := g.idToVertex[toID]
+
+		// Get the edge type
+		edgeKey := fmt.Sprintf("%d->%d", fromID, toID)
+		edgeType := g.edgeTypes[edgeKey]
+
+		edges = append(edges, Edge[EdgeType, VertexType]{From: from, To: to, Edge: edgeType})
+	}
+
+	return edges
+}
+
+// GetReverseAdjacentVertices returns all the edges that terminate at the given vertex.
+func (g *Graph[EdgeType, VertexType]) GetReverseAdjacentVertices(to VertexType) []Edge[EdgeType, VertexType] {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	toID, exists := g.vertexToID[to]
+	if !exists {
+		return []Edge[EdgeType, VertexType]{}
+	}
+
+	edges := []Edge[EdgeType, VertexType]{}
+	fromNodes := g.gonumGraph.To(toID)
+	for fromNodes.Next() {
+		fromID := fromNodes.Node().ID()
+		from := g.idToVertex[fromID]
+
+		// Get the edge type
+		edgeKey := fmt.Sprintf("%d->%d", fromID, toID)
+		edgeType := g.edgeTypes[edgeKey]
+
+		edges = append(edges, Edge[EdgeType, VertexType]{From: from, To: to, Edge: edgeType})
+	}
+
+	return edges
+}
+
+// getOrCreateVertexID returns the ID for a vertex, creating it if it doesn't exist.
+func (g *Graph[EdgeType, VertexType]) getOrCreateVertexID(vertex VertexType) int64 {
+	if id, exists := g.vertexToID[vertex]; exists {
+		return id
+	}
+
+	id := g.nextID
+	g.nextID++
+	g.vertexToID[vertex] = id
+	g.idToVertex[id] = vertex
+
+	// Add the node to the gonum graph
+	g.gonumGraph.AddNode(simple.Node(id))
+
+	return id
+}
+
+// canReach checks if there is a path from the start vertex to the end vertex.
+func (g *Graph[EdgeType, VertexType]) canReach(start, end VertexType) bool {
+	if start == end {
+		return true
+	}
+
+	startID, startExists := g.vertexToID[start]
+	endID, endExists := g.vertexToID[end]
+
+	if !startExists || !endExists {
+		return false
+	}
+
+	// Use gonum's built-in path existence check
+	return topo.PathExistsIn(g.gonumGraph, simple.Node(startID), simple.Node(endID))
+}
+
+// ToDOT exports the graph to DOT format for visualization
+func (g *Graph[EdgeType, VertexType]) ToDOT(name string) (string, error) {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	if g.gonumGraph == nil {
+		return "", xerrors.New("graph is not initialized")
+	}
+
+	// Marshal the graph to DOT format
+	dotBytes, err := dot.Marshal(g.gonumGraph, name, "", "  ")
+	if err != nil {
+		return "", xerrors.Errorf("failed to marshal graph to DOT: %w", err)
+	}
+
+	return string(dotBytes), nil
+}

agent/unit/graph_test.go

@@ -0,0 +1,454 @@
+// Package unit_test provides tests for the unit package.
+//
+// DOT Graph Testing:
+// The graph tests use golden files for DOT representation verification.
+// To update the golden files:
+// make gen/golden-files
+//
+// The golden files contain the expected DOT representation and can be easily
+// inspected, version controlled, and updated when the graph structure changes.
+package unit_test
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/agent/unit"
+	"github.com/coder/coder/v2/cryptorand"
+)
+
+type testGraphEdge string
+
+const (
+	testEdgeStarted   testGraphEdge = "started"
+	testEdgeCompleted testGraphEdge = "completed"
+)
+
+type testGraphVertex struct {
+	Name string
+}
+
+type (
+	testGraph = unit.Graph[testGraphEdge, *testGraphVertex]
+	testEdge  = unit.Edge[testGraphEdge, *testGraphVertex]
+)
+
+// randInt generates a random integer in the range [0, limit).
+func randInt(limit int) int {
+	if limit <= 0 {
+		return 0
+	}
+	n, err := cryptorand.Int63n(int64(limit))
+	if err != nil {
+		return 0
+	}
+	return int(n)
+}
+
+// UpdateGoldenFiles indicates golden files should be updated.
+// To update the golden files:
+// make gen/golden-files
+var UpdateGoldenFiles = flag.Bool("update", false, "update .golden files")
+
+// assertDOTGraph requires that the graph's DOT representation matches the golden file
+func assertDOTGraph(t *testing.T, graph *testGraph, goldenName string) {
+	t.Helper()
+
+	dot, err := graph.ToDOT(goldenName)
+	require.NoError(t, err)
+
+	goldenFile := filepath.Join("testdata", goldenName+".golden")
+	if *UpdateGoldenFiles {
+		t.Logf("update golden file for: %q: %s", goldenName, goldenFile)
+		err := os.MkdirAll(filepath.Dir(goldenFile), 0o755)
+		require.NoError(t, err, "want no error creating golden file directory")
+		err = os.WriteFile(goldenFile, []byte(dot), 0o600)
+		require.NoError(t, err, "update golden file")
+	}
+
+	expected, err := os.ReadFile(goldenFile)
+	require.NoError(t, err, "read golden file, run \"make gen/golden-files\" and commit the changes")
+
+	// Normalize line endings for cross-platform compatibility
+	expected = normalizeLineEndings(expected)
+	normalizedDot := normalizeLineEndings([]byte(dot))
+
+	assert.Empty(t, cmp.Diff(string(expected), string(normalizedDot)), "golden file mismatch (-want +got): %s, run \"make gen/golden-files\", verify and commit the changes", goldenFile)
+}
+
+// normalizeLineEndings ensures that all line endings are normalized to \n.
+// Required for Windows compatibility.
+func normalizeLineEndings(content []byte) []byte {
+	content = bytes.ReplaceAll(content, []byte("\r\n"), []byte("\n"))
+	content = bytes.ReplaceAll(content, []byte("\r"), []byte("\n"))
+	return content
+}
+
+func TestGraph(t *testing.T) {
+	t.Parallel()
+
+	testFuncs := map[string]func(t *testing.T) *unit.Graph[testGraphEdge, *testGraphVertex]{
+		"ForwardAndReverseEdges": func(t *testing.T) *unit.Graph[testGraphEdge, *testGraphVertex] {
+			graph := &unit.Graph[testGraphEdge, *testGraphVertex]{}
+			unit1 := &testGraphVertex{Name: "unit1"}
+			unit2 := &testGraphVertex{Name: "unit2"}
+			unit3 := &testGraphVertex{Name: "unit3"}
+			err := graph.AddEdge(unit1, unit2, testEdgeCompleted)
+			require.NoError(t, err)
+			err = graph.AddEdge(unit1, unit3, testEdgeStarted)
+			require.NoError(t, err)
+
+			// Check for forward edge
+			vertices := graph.GetForwardAdjacentVertices(unit1)
+			require.Len(t, vertices, 2)
+			// Unit 1 depends on the completion of Unit2
+			require.Contains(t, vertices, testEdge{
+				From: unit1,
+				To:   unit2,
+				Edge: testEdgeCompleted,
+			})
+			// Unit 1 depends on the start of Unit3
+			require.Contains(t, vertices, testEdge{
+				From: unit1,
+				To:   unit3,
+				Edge: testEdgeStarted,
+			})
+
+			// Check for reverse edges
+			unit2ReverseEdges := graph.GetReverseAdjacentVertices(unit2)
+			require.Len(t, unit2ReverseEdges, 1)
+			// Unit 2 must be completed before Unit 1 can start
+			require.Contains(t, unit2ReverseEdges, testEdge{
+				From: unit1,
+				To:   unit2,
+				Edge: testEdgeCompleted,
+			})
+
+			unit3ReverseEdges := graph.GetReverseAdjacentVertices(unit3)
+			require.Len(t, unit3ReverseEdges, 1)
+			// Unit 3 must be started before Unit 1 can complete
+			require.Contains(t, unit3ReverseEdges, testEdge{
+				From: unit1,
+				To:   unit3,
+				Edge: testEdgeStarted,
+			})
+
+			return graph
+		},
+		"SelfReference": func(t *testing.T) *testGraph {
+			graph := &testGraph{}
+			unit1 := &testGraphVertex{Name: "unit1"}
+			err := graph.AddEdge(unit1, unit1, testEdgeCompleted)
+			require.Error(t, err)
+			require.ErrorContains(t, err, fmt.Sprintf("adding edge (%v -> %v) would create a cycle", unit1, unit1))
+
+			return graph
+		},
+		"Cycle": func(t *testing.T) *testGraph {
+			graph := &testGraph{}
+			unit1 := &testGraphVertex{Name: "unit1"}
+			unit2 := &testGraphVertex{Name: "unit2"}
+			err := graph.AddEdge(unit1, unit2, testEdgeCompleted)
+			require.NoError(t, err)
+			err = graph.AddEdge(unit2, unit1, testEdgeStarted)
+			require.Error(t, err)
+			require.ErrorContains(t, err, fmt.Sprintf("adding edge (%v -> %v) would create a cycle", unit2, unit1))
+
+			return graph
+		},
+		"MultipleDependenciesSameStatus": func(t *testing.T) *testGraph {
+			graph := &testGraph{}
+			unit1 := &testGraphVertex{Name: "unit1"}
+			unit2 := &testGraphVertex{Name: "unit2"}
+			unit3 := &testGraphVertex{Name: "unit3"}
+			unit4 := &testGraphVertex{Name: "unit4"}
+
+			// Unit1 depends on completion of both unit2 and unit3 (same status type)
+			err := graph.AddEdge(unit1, unit2, testEdgeCompleted)
+			require.NoError(t, err)
+			err = graph.AddEdge(unit1, unit3, testEdgeCompleted)
+			require.NoError(t, err)
+
+			// Unit1 also depends on starting of unit4 (different status type)
+			err = graph.AddEdge(unit1, unit4, testEdgeStarted)
+			require.NoError(t, err)
+
+			// Check that unit1 has 3 forward dependencies
+			forwardEdges := graph.GetForwardAdjacentVertices(unit1)
+			require.Len(t, forwardEdges, 3)
+
+			// Verify all expected dependencies exist
+			expectedDependencies := []testEdge{
+				{From: unit1, To: unit2, Edge: testEdgeCompleted},
+				{From: unit1, To: unit3, Edge: testEdgeCompleted},
+				{From: unit1, To: unit4, Edge: testEdgeStarted},
+			}
+
+			for _, expected := range expectedDependencies {
+				require.Contains(t, forwardEdges, expected)
+			}
+
+			// Check reverse dependencies
+			unit2ReverseEdges := graph.GetReverseAdjacentVertices(unit2)
+			require.Len(t, unit2ReverseEdges, 1)
+			require.Contains(t, unit2ReverseEdges, testEdge{
+				From: unit1, To: unit2, Edge: testEdgeCompleted,
+			})
+
+			unit3ReverseEdges := graph.GetReverseAdjacentVertices(unit3)
+			require.Len(t, unit3ReverseEdges, 1)
+			require.Contains(t, unit3ReverseEdges, testEdge{
+				From: unit1, To: unit3, Edge: testEdgeCompleted,
+			})
+
+			unit4ReverseEdges := graph.GetReverseAdjacentVertices(unit4)
+			require.Len(t, unit4ReverseEdges, 1)
+			require.Contains(t, unit4ReverseEdges, testEdge{
+				From: unit1, To: unit4, Edge: testEdgeStarted,
+			})
+
+			return graph
+		},
+	}
+
+	for testName, testFunc := range testFuncs {
+		var graph *testGraph
+		t.Run(testName, func(t *testing.T) {
+			t.Parallel()
+			graph = testFunc(t)
+			assertDOTGraph(t, graph, testName)
+		})
+	}
+}
+
+func TestGraphThreadSafety(t *testing.T) {
+	t.Parallel()
+
+	t.Run("ConcurrentReadWrite", func(t *testing.T) {
+		t.Parallel()
+
+		graph := &testGraph{}
+		var wg sync.WaitGroup
+		const numWriters = 50
+		const numReaders = 100
+		const operationsPerWriter = 1000
+		const operationsPerReader = 2000
+
+		barrier := make(chan struct{})
+		// Launch writers
+		for i := 0; i < numWriters; i++ {
+			wg.Add(1)
+			go func(writerID int) {
+				defer wg.Done()
+				<-barrier
+				for j := 0; j < operationsPerWriter; j++ {
+					from := &testGraphVertex{Name: fmt.Sprintf("writer-%d-%d", writerID, j)}
+					to := &testGraphVertex{Name: fmt.Sprintf("writer-%d-%d", writerID, j+1)}
+					graph.AddEdge(from, to, testEdgeCompleted)
+				}
+			}(i)
+		}
+
+		// Launch readers
+		readerResults := make([]struct {
+			panicked  bool
+			readCount int
+		}, numReaders)
+
+		for i := 0; i < numReaders; i++ {
+			wg.Add(1)
+			go func(readerID int) {
+				defer wg.Done()
+				<-barrier
+				defer func() {
+					if r := recover(); r != nil {
+						readerResults[readerID].panicked = true
+					}
+				}()
+
+				readCount := 0
+				for j := 0; j < operationsPerReader; j++ {
+					// Create a test vertex and read
+					testUnit := &testGraphVertex{Name: fmt.Sprintf("test-reader-%d-%d", readerID, j)}
+					forwardEdges := graph.GetForwardAdjacentVertices(testUnit)
+					reverseEdges := graph.GetReverseAdjacentVertices(testUnit)
+
+					// Just verify no panics (results may be nil for non-existent vertices)
+					_ = forwardEdges
+					_ = reverseEdges
+					readCount++
+				}
+				readerResults[readerID].readCount = readCount
+			}(i)
+		}
+
+		close(barrier)
+		wg.Wait()
+
+		// Verify no panics occurred in readers
+		for i, result := range readerResults {
+			require.False(t, result.panicked, "reader %d panicked", i)
+			require.Equal(t, operationsPerReader, result.readCount, "reader %d should have performed expected reads", i)
+		}
+	})
+
+	t.Run("ConcurrentCycleDetection", func(t *testing.T) {
+		t.Parallel()
+
+		graph := &testGraph{}
+
+		// Pre-create chain: A→B→C→D
+		unitA := &testGraphVertex{Name: "A"}
+		unitB := &testGraphVertex{Name: "B"}
+		unitC := &testGraphVertex{Name: "C"}
+		unitD := &testGraphVertex{Name: "D"}
+
+		err := graph.AddEdge(unitA, unitB, testEdgeCompleted)
+		require.NoError(t, err)
+		err = graph.AddEdge(unitB, unitC, testEdgeCompleted)
+		require.NoError(t, err)
+		err = graph.AddEdge(unitC, unitD, testEdgeCompleted)
+		require.NoError(t, err)
+
+		barrier := make(chan struct{})
+		var wg sync.WaitGroup
+		const numGoroutines = 50
+		cycleErrors := make([]error, numGoroutines)
+
+		// Launch goroutines trying to add D→A (creates cycle)
+		for i := 0; i < numGoroutines; i++ {
+			wg.Add(1)
+			go func(goroutineID int) {
+				defer wg.Done()
+				<-barrier
+				err := graph.AddEdge(unitD, unitA, testEdgeCompleted)
+				cycleErrors[goroutineID] = err
+			}(i)
+		}
+
+		close(barrier)
+		wg.Wait()
+
+		// Verify all attempts correctly returned cycle error
+		for i, err := range cycleErrors {
+			require.Error(t, err, "goroutine %d should have detected cycle", i)
+			require.Contains(t, err.Error(), "would create a cycle")
+		}
+
+		// Verify graph remains valid (original chain intact)
+		dot, err := graph.ToDOT("test")
+		require.NoError(t, err)
+		require.NotEmpty(t, dot)
+	})
+
+	t.Run("ConcurrentToDOT", func(t *testing.T) {
+		t.Parallel()
+
+		graph := &testGraph{}
+
+		// Pre-populate graph
+		for i := 0; i < 20; i++ {
+			from := &testGraphVertex{Name: fmt.Sprintf("dot-unit-%d", i)}
+			to := &testGraphVertex{Name: fmt.Sprintf("dot-unit-%d", i+1)}
+			err := graph.AddEdge(from, to, testEdgeCompleted)
+			require.NoError(t, err)
+		}
+
+		barrier := make(chan struct{})
+		var wg sync.WaitGroup
+		const numReaders = 100
+		const numWriters = 20
+		dotResults := make([]string, numReaders)
+
+		// Launch readers calling ToDOT
+		dotErrors := make([]error, numReaders)
+		for i := 0; i < numReaders; i++ {
+			wg.Add(1)
+			go func(readerID int) {
+				defer wg.Done()
+				<-barrier
+				dot, err := graph.ToDOT(fmt.Sprintf("test-%d", readerID))
+				dotErrors[readerID] = err
+				if err == nil {
+					dotResults[readerID] = dot
+				}
+			}(i)
+		}
+
+		// Launch writers adding edges
+		for i := 0; i < numWriters; i++ {
+			wg.Add(1)
+			go func(writerID int) {
+				defer wg.Done()
+				<-barrier
+				from := &testGraphVertex{Name: fmt.Sprintf("writer-dot-%d", writerID)}
+				to := &testGraphVertex{Name: fmt.Sprintf("writer-dot-target-%d", writerID)}
+				graph.AddEdge(from, to, testEdgeCompleted)
+			}(i)
+		}
+
+		close(barrier)
+		wg.Wait()
+
+		// Verify no errors occurred during DOT generation
+		for i, err := range dotErrors {
+			require.NoError(t, err, "DOT generation error at index %d", i)
+		}
+
+		// Verify all DOT results are valid
+		for i, dot := range dotResults {
+			require.NotEmpty(t, dot, "DOT result %d should not be empty", i)
+		}
+	})
+}
+
+func BenchmarkGraph_ConcurrentMixedOperations(b *testing.B) {
+	graph := &testGraph{}
+	var wg sync.WaitGroup
+	const numGoroutines = 200
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		// Launch goroutines performing random operations
+		for j := 0; j < numGoroutines; j++ {
+			wg.Add(1)
+			go func(goroutineID int) {
+				defer wg.Done()
+				operationCount := 0
+
+				for operationCount < 50 {
+					operation := float32(randInt(100)) / 100.0
+
+					if operation < 0.6 { // 60% reads
+						// Read operation
+						testUnit := &testGraphVertex{Name: fmt.Sprintf("bench-read-%d-%d", goroutineID, operationCount)}
+						forwardEdges := graph.GetForwardAdjacentVertices(testUnit)
+						reverseEdges := graph.GetReverseAdjacentVertices(testUnit)
+
+						// Just verify no panics (results may be nil for non-existent vertices)
+						_ = forwardEdges
+						_ = reverseEdges
+					} else { // 40% writes
+						// Write operation
+						from := &testGraphVertex{Name: fmt.Sprintf("bench-write-%d-%d", goroutineID, operationCount)}
+						to := &testGraphVertex{Name: fmt.Sprintf("bench-write-target-%d-%d", goroutineID, operationCount)}
+						graph.AddEdge(from, to, testEdgeCompleted)
+					}
+
+					operationCount++
+				}
+			}(j)
+		}
+
+		wg.Wait()
+	}
+}

agent/unit/testdata/Cycle.golden

@@ -0,0 +1,8 @@
+strict digraph Cycle {
+  // Node definitions.
+  1;
+  2;
+
+  // Edge definitions.
+  1 -> 2;
+}

agent/unit/testdata/ForwardAndReverseEdges.golden

@@ -0,0 +1,10 @@
+strict digraph ForwardAndReverseEdges {
+  // Node definitions.
+  1;
+  2;
+  3;
+
+  // Edge definitions.
+  1 -> 2;
+  1 -> 3;
+}

agent/unit/testdata/MultipleDependenciesSameStatus.golden

@@ -0,0 +1,12 @@
+strict digraph MultipleDependenciesSameStatus {
+  // Node definitions.
+  1;
+  2;
+  3;
+  4;
+
+  // Edge definitions.
+  1 -> 2;
+  1 -> 3;
+  1 -> 4;
+}

agent/unit/testdata/SelfReference.golden

@@ -0,0 +1,4 @@
+strict digraph SelfReference {
+  // Node definitions.
+  1;
+}

go.mod

@@ -486,6 +486,7 @@ require (
 	github.com/go-git/go-git/v5 v5.16.2
 	github.com/icholy/replace v0.6.0
 	github.com/mark3labs/mcp-go v0.38.0
+	gonum.org/v1/gonum v0.16.0
 )
 
 require (