diff --git a/src/Fallout.Build/Execution/Extensions/BuildGraphUtility.cs b/src/Fallout.Build/Execution/Extensions/BuildGraphUtility.cs
new file mode 100644
index 000000000..cda806ffd
--- /dev/null
+++ b/src/Fallout.Build/Execution/Extensions/BuildGraphUtility.cs
@@ -0,0 +1,99 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text.Json;
+using Fallout.Common.Execution;
+using Fallout.Common.Utilities;
+
+namespace Fallout.Build.Execution.Extensions;
+
+/// <summary>
+/// Pure projection of the target graph into the <c>build-graph.json</c> shape consumed by editor
+/// tooling (the VS Code extension): schema version, the running Fallout version, and for each target
+/// its name, description, declaring type, the default/listed flags, and the four relation kinds.
+/// <para>
+/// This is the machine-readable contract the extension gates on — the JSON shape must stay stable.
+/// Any breaking change to it requires bumping <see cref="SchemaVersion"/>. The projection is kept
+/// separate from <see cref="SerializeBuildGraphAttribute"/> (which owns the build-lifecycle hook and
+/// file I/O) so the contract can be snapshot-tested without driving a build.
+/// </para>
+/// </summary>
+internal static class BuildGraphUtility
+{
+    /// <summary>Schema version consumers gate on; bump only on a breaking shape change.</summary>
+    internal const int SchemaVersion = 1;
+
+    private static readonly JsonSerializerOptions serializerOptions =
+        new()
+        {
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+            WriteIndented = true,
+        };
+
+    /// <summary>Projects the targets into the serializable graph model.</summary>
+    /// <param name="targets">The build's executable targets, in any order.</param>
+    /// <param name="falloutVersion">The running Fallout version, or <c>null</c> for a local/dev build.</param>
+    internal static BuildGraphModel GetModel(
+        IReadOnlyCollection<ExecutableTarget> targets,
+        string falloutVersion)
+        => new(
+            SchemaVersion,
+            falloutVersion,
+            targets
+                .OrderBy(x => x.Name, StringComparer.Ordinal)
+                .Select(ToModel)
+                .ToList());
+
+    /// <summary>Serializes the graph model to the exact JSON written into <c>build-graph.json</c>.</summary>
+    internal static string GetJsonString(
+        IReadOnlyCollection<ExecutableTarget> targets,
+        string falloutVersion)
+        => GetModel(targets, falloutVersion).ToJson(serializerOptions);
+
+    // Takes the informational version up to the build-metadata separator ('+'), so the pin aligns with
+    // the running tool. Returns the input unchanged when there is no separator, and null only when the
+    // input is null/empty (e.g. a local build with no version stamped).
+    internal static string NormalizeVersion(string informationalVersion)
+    {
+        if (string.IsNullOrEmpty(informationalVersion))
+        {
+            return null;
+        }
+
+        var plusIndex = informationalVersion.IndexOf('+');
+        return plusIndex == -1 ? informationalVersion : informationalVersion[..plusIndex];
+    }
+
+    private static TargetModel ToModel(ExecutableTarget target)
+        => new(
+            target.Name,
+            target.Description,
+            target.Member?.DeclaringType?.Name,
+            target.IsDefault,
+            target.Listed,
+            SortedNames(target.ExecutionDependencies),
+            SortedNames(target.OrderDependencies),
+            SortedNames(target.TriggerDependencies),
+            SortedNames(target.Triggers));
+
+    // Sorted for deterministic output — the graph carries no execution order, so the display
+    // order is irrelevant to consumers and a stable ordering avoids spurious file churn.
+    private static IReadOnlyList<string> SortedNames(IEnumerable<ExecutableTarget> targets)
+        => targets.Select(x => x.Name).OrderBy(x => x, StringComparer.Ordinal).ToList();
+
+    internal sealed record BuildGraphModel(
+        int Version,
+        string FalloutVersion,
+        IReadOnlyList<TargetModel> Targets);
+
+    internal sealed record TargetModel(
+        string Name,
+        string Description,
+        string DeclaredIn,
+        bool Default,
+        bool Listed,
+        IReadOnlyList<string> DependsOn,
+        IReadOnlyList<string> After,
+        IReadOnlyList<string> TriggeredBy,
+        IReadOnlyList<string> Triggers);
+}
diff --git a/src/Fallout.Build/Execution/Extensions/SerializeBuildGraphAttribute.cs b/src/Fallout.Build/Execution/Extensions/SerializeBuildGraphAttribute.cs
new file mode 100644
index 000000000..a621f3847
--- /dev/null
+++ b/src/Fallout.Build/Execution/Extensions/SerializeBuildGraphAttribute.cs
@@ -0,0 +1,45 @@
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using Fallout.Common.Execution;
+using Fallout.Common.IO;
+
+namespace Fallout.Build.Execution.Extensions;
+
+/// <summary>
+/// Emits <c>build-graph.json</c> into the temporary directory on every build initialization,
+/// giving editor tooling (the VS Code extension) a machine-readable projection of the target
+/// graph. The projection itself lives in <see cref="BuildGraphUtility"/>; this attribute only owns
+/// the build-lifecycle hook and the file write. Best-effort — a serialization failure never fails
+/// the build.
+/// </summary>
+internal class SerializeBuildGraphAttribute : BuildExtensionAttributeBase, IOnBuildInitialized
+{
+    private const string GraphFileName = "build-graph.json";
+
+    private AbsolutePath GraphFile => Build.TemporaryDirectory / GraphFileName;
+
+    public void OnBuildInitialized(
+        IReadOnlyCollection<ExecutableTarget> executableTargets,
+        IReadOnlyCollection<ExecutableTarget> executionPlan)
+    {
+        try
+        {
+            var json = BuildGraphUtility.GetJsonString(executableTargets, FindFalloutVersion());
+            GraphFile.WriteAllText(json);
+        }
+        catch (Exception exception)
+        {
+            // Emission is a convenience for editor tooling — never let it break a build.
+            Serilog.Log.Verbose(exception, "Failed to emit {GraphFileName}", GraphFileName);
+        }
+    }
+
+    // Mirrors Fallout.Migrate: the informational version of the running Fallout assembly, up to the
+    // build-metadata separator, so the pin aligns with the running tool. Null when unstamped.
+    private static string FindFalloutVersion()
+        => BuildGraphUtility.NormalizeVersion(
+            typeof(SerializeBuildGraphAttribute).Assembly
+                .GetCustomAttribute<AssemblyInformationalVersionAttribute>()
+                ?.InformationalVersion);
+}
diff --git a/src/Fallout.Build/FalloutBuild.cs b/src/Fallout.Build/FalloutBuild.cs
index af8573875..a604cccc8 100644
--- a/src/Fallout.Build/FalloutBuild.cs
+++ b/src/Fallout.Build/FalloutBuild.cs
@@ -52,6 +52,7 @@ namespace Fallout.Common;
 // [SaveBuildProfile(Priority = 30)]
 // [LoadBuildProfiles(Priority = 25)]
 // After logo
+[SerializeBuildGraph(Priority = 20)]
 [HandlePlanRequests(Priority = 10)]
 [HandleHelpRequests(Priority = 5)]
 [Telemetry]
diff --git a/tests/Fallout.Build.Specs/BuildGraphUtilitySpecs.Empty_graph_matches_the_contract_snapshot.verified.json b/tests/Fallout.Build.Specs/BuildGraphUtilitySpecs.Empty_graph_matches_the_contract_snapshot.verified.json
new file mode 100644
index 000000000..6dfd4a355
--- /dev/null
+++ b/tests/Fallout.Build.Specs/BuildGraphUtilitySpecs.Empty_graph_matches_the_contract_snapshot.verified.json
@@ -0,0 +1,5 @@
+{
+  "version": 1,
+  "falloutVersion": null,
+  "targets": []
+}
\ No newline at end of file
diff --git a/tests/Fallout.Build.Specs/BuildGraphUtilitySpecs.Sample_graph_matches_the_contract_snapshot.verified.json b/tests/Fallout.Build.Specs/BuildGraphUtilitySpecs.Sample_graph_matches_the_contract_snapshot.verified.json
new file mode 100644
index 000000000..67baa6095
--- /dev/null
+++ b/tests/Fallout.Build.Specs/BuildGraphUtilitySpecs.Sample_graph_matches_the_contract_snapshot.verified.json
@@ -0,0 +1,60 @@
+{
+  "version": 1,
+  "falloutVersion": "2026.1.0-preview.42",
+  "targets": [
+    {
+      "name": "Compile",
+      "description": "Builds all projects",
+      "declaredIn": "SampleBuild",
+      "default": false,
+      "listed": true,
+      "dependsOn": [
+        "Restore"
+      ],
+      "after": [],
+      "triggeredBy": [],
+      "triggers": [
+        "Publish"
+      ]
+    },
+    {
+      "name": "Publish",
+      "description": null,
+      "declaredIn": null,
+      "default": false,
+      "listed": false,
+      "dependsOn": [],
+      "after": [],
+      "triggeredBy": [
+        "Test"
+      ],
+      "triggers": []
+    },
+    {
+      "name": "Restore",
+      "description": null,
+      "declaredIn": null,
+      "default": false,
+      "listed": true,
+      "dependsOn": [],
+      "after": [],
+      "triggeredBy": [],
+      "triggers": []
+    },
+    {
+      "name": "Test",
+      "description": null,
+      "declaredIn": null,
+      "default": true,
+      "listed": true,
+      "dependsOn": [
+        "Compile"
+      ],
+      "after": [
+        "Restore"
+      ],
+      "triggeredBy": [],
+      "triggers": []
+    }
+  ]
+}
\ No newline at end of file
diff --git a/tests/Fallout.Build.Specs/BuildGraphUtilitySpecs.cs b/tests/Fallout.Build.Specs/BuildGraphUtilitySpecs.cs
new file mode 100644
index 000000000..38776eb30
--- /dev/null
+++ b/tests/Fallout.Build.Specs/BuildGraphUtilitySpecs.cs
@@ -0,0 +1,171 @@
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Text.Json;
+using System.Threading.Tasks;
+using Fallout.Build.Execution.Extensions;
+using Fallout.Common.Execution;
+using FluentAssertions;
+using VerifyXunit;
+using Xunit;
+
+namespace Fallout.Common.Specs.Execution;
+
+/// <summary>
+/// Contract tests for <c>build-graph.json</c>. This JSON is consumed by the VS Code extension, so the
+/// shape must not drift silently — the verified snapshots below are the contract. A change that fails
+/// them is a schema change and demands bumping <see cref="BuildGraphUtility.SchemaVersion"/> plus a
+/// matching update on the extension side.
+/// </summary>
+public class BuildGraphUtilitySpecs
+{
+    private const string SampleVersion = "2026.1.0-preview.42";
+
+    // A representative graph exercising every emitted field and relation kind.
+    private static IReadOnlyCollection<ExecutableTarget> SampleGraph()
+    {
+        var restore = new ExecutableTarget { Name = "Restore", Listed = true };
+        var compile = new ExecutableTarget
+                      {
+                          Name = "Compile",
+                          Description = "Builds all projects",
+                          Listed = true,
+                          Member = MemberOf(nameof(SampleBuild.Compile)),
+                      };
+        var test = new ExecutableTarget { Name = "Test", Listed = true, IsDefault = true };
+        var publish = new ExecutableTarget { Name = "Publish", Listed = false };
+
+        compile.ExecutionDependencies.Add(restore);
+        test.ExecutionDependencies.Add(compile);
+        test.OrderDependencies.Add(restore);
+        publish.TriggerDependencies.Add(test);
+        compile.Triggers.Add(publish);
+
+        // Deliberately unsorted so the ordinal ordering guarantee is exercised.
+        return new[] { test, publish, compile, restore };
+    }
+
+    [Fact]
+    public Task Sample_graph_matches_the_contract_snapshot()
+        => Verifier.Verify(BuildGraphUtility.GetJsonString(SampleGraph(), SampleVersion), "json");
+
+    [Fact]
+    public Task Empty_graph_matches_the_contract_snapshot()
+        => Verifier.Verify(BuildGraphUtility.GetJsonString(new ExecutableTarget[0], falloutVersion: null), "json");
+
+    [Fact]
+    public void Schema_version_is_1()
+    {
+        // A change here is a breaking contract change — update the VS Code extension's
+        // SUPPORTED_SCHEMA_VERSION and this guard together, deliberately.
+        BuildGraphUtility.SchemaVersion.Should().Be(1);
+    }
+
+    [Fact]
+    public void Targets_are_ordered_by_name_ordinally()
+    {
+        var model = BuildGraphUtility.GetModel(SampleGraph(), SampleVersion);
+
+        model.Targets.Select(x => x.Name).Should().Equal("Compile", "Publish", "Restore", "Test");
+    }
+
+    [Fact]
+    public void Relation_kinds_map_to_their_own_fields()
+    {
+        var compile = ModelFor("Compile");
+        var test = ModelFor("Test");
+        var publish = ModelFor("Publish");
+
+        compile.DependsOn.Should().Equal("Restore");
+        compile.Triggers.Should().Equal("Publish");
+        test.DependsOn.Should().Equal("Compile");
+        test.After.Should().Equal("Restore");
+        publish.TriggeredBy.Should().Equal("Test");
+    }
+
+    [Fact]
+    public void Dependency_lists_are_ordered_ordinally()
+    {
+        var target = new ExecutableTarget { Name = "Root" };
+        target.ExecutionDependencies.Add(new ExecutableTarget { Name = "Zebra" });
+        target.ExecutionDependencies.Add(new ExecutableTarget { Name = "Alpha" });
+        target.ExecutionDependencies.Add(new ExecutableTarget { Name = "Mango" });
+
+        var model = BuildGraphUtility.GetModel(new[] { target }, SampleVersion).Targets.Single();
+
+        model.DependsOn.Should().Equal("Alpha", "Mango", "Zebra");
+    }
+
+    [Fact]
+    public void Default_and_listed_flags_are_projected()
+    {
+        var test = ModelFor("Test");
+        var publish = ModelFor("Publish");
+
+        test.Default.Should().BeTrue();
+        test.Listed.Should().BeTrue();
+        publish.Default.Should().BeFalse();
+        publish.Listed.Should().BeFalse();
+    }
+
+    [Fact]
+    public void DeclaredIn_is_the_declaring_type_simple_name_or_null()
+    {
+        ModelFor("Compile").DeclaredIn.Should().Be(nameof(SampleBuild));
+        // Restore has no backing member, so there is nothing to disambiguate go-to-definition with.
+        ModelFor("Restore").DeclaredIn.Should().BeNull();
+    }
+
+    [Fact]
+    public void Optional_string_fields_are_emitted_as_null_rather_than_omitted()
+    {
+        // The extension's Target interface marks description/declaredIn optional; we keep the keys
+        // present (as null) for a stable shape, so consumers can rely on the property existing.
+        using var doc = JsonDocument.Parse(BuildGraphUtility.GetJsonString(SampleGraph(), falloutVersion: null));
+
+        doc.RootElement.GetProperty("falloutVersion").ValueKind.Should().Be(JsonValueKind.Null);
+
+        var restore = doc.RootElement.GetProperty("targets").EnumerateArray()
+            .Single(x => x.GetProperty("name").GetString() == "Restore");
+        restore.GetProperty("description").ValueKind.Should().Be(JsonValueKind.Null);
+        restore.GetProperty("declaredIn").ValueKind.Should().Be(JsonValueKind.Null);
+    }
+
+    [Fact]
+    public void Root_and_target_property_names_are_camelCase()
+    {
+        using var doc = JsonDocument.Parse(BuildGraphUtility.GetJsonString(SampleGraph(), SampleVersion));
+
+        doc.RootElement.EnumerateObject().Select(x => x.Name)
+            .Should().Equal("version", "falloutVersion", "targets");
+
+        var firstTarget = doc.RootElement.GetProperty("targets").EnumerateArray().First();
+        firstTarget.EnumerateObject().Select(x => x.Name)
+            .Should().Equal(
+                "name", "description", "declaredIn", "default", "listed",
+                "dependsOn", "after", "triggeredBy", "triggers");
+    }
+
+    [Theory]
+    [InlineData("2026.1.0-preview.42+abc123", "2026.1.0-preview.42")]
+    [InlineData("2026.1.0", "2026.1.0")]
+    [InlineData("10.0.0-rc.1", "10.0.0-rc.1")]
+    [InlineData("", null)]
+    [InlineData(null, null)]
+    public void NormalizeVersion_strips_build_metadata(string input, string expected)
+    {
+        BuildGraphUtility.NormalizeVersion(input).Should().Be(expected);
+    }
+
+    private static BuildGraphUtility.TargetModel ModelFor(string name)
+        => BuildGraphUtility.GetModel(SampleGraph(), SampleVersion).Targets.Single(x => x.Name == name);
+
+    private static MemberInfo MemberOf(string name)
+        => typeof(SampleBuild).GetProperty(name, BindingFlags.Instance | BindingFlags.Public);
+
+    // Backing type whose name flows into `declaredIn`.
+    private class SampleBuild
+    {
+        public object Compile => null;
+    }
+}