diff --git a/server/NeonSprawl.Server.Tests/Game/Npc/NpcBehaviorDefinitionRegistryTests.cs b/server/NeonSprawl.Server.Tests/Game/Npc/NpcBehaviorDefinitionRegistryTests.cs
new file mode 100644
index 0000000..0f28a8e
--- /dev/null
+++ b/server/NeonSprawl.Server.Tests/Game/Npc/NpcBehaviorDefinitionRegistryTests.cs
@@ -0,0 +1,302 @@
+using System.IO;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using NeonSprawl.Server.Game.Npc;
+using NeonSprawl.Server.Tests;
+using Xunit;
+
+namespace NeonSprawl.Server.Tests.Game.Npc;
+
+public class NpcBehaviorDefinitionRegistryTests
+{
+    private static NpcBehaviorDefinitionRegistry CreateRegistryFromRows(IReadOnlyDictionary<string, NpcBehaviorDefRow> byId)
+    {
+        var catalog = new NpcBehaviorDefinitionCatalog("/tmp/npc-behaviors", byId, catalogJsonFileCount: 1);
+        return new NpcBehaviorDefinitionRegistry(catalog);
+    }
+
+    private static NpcBehaviorDefRow MeleeRow() =>
+        new(
+            PrototypeNpcBehaviorRegistry.PrototypeMeleePressure,
+            "Melee Pressure",
+            "melee_pressure",
+            100,
+            8.0,
+            16.0,
+            1.5,
+            15,
+            3.0);
+
+    private static NpcBehaviorDefRow RangedRow() =>
+        new(
+            PrototypeNpcBehaviorRegistry.PrototypeRangedControl,
+            "Ranged Control",
+            "ranged_control",
+            80,
+            10.0,
+            20.0,
+            2.0,
+            12,
+            4.0);
+
+    private static NpcBehaviorDefRow EliteRow() =>
+        new(
+            PrototypeNpcBehaviorRegistry.PrototypeEliteMiniBoss,
+            "Elite Mini-Boss",
+            "elite_mini_boss",
+            200,
+            8.0,
+            18.0,
+            2.5,
+            25,
+            5.0);
+
+    [Fact]
+    public void TryGetDefinition_ShouldReturnTrueAndExpectedMetadata_WhenMeleeExists()
+    {
+        // Arrange
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal)
+        {
+            [PrototypeNpcBehaviorRegistry.PrototypeMeleePressure] = MeleeRow(),
+        };
+        var registry = CreateRegistryFromRows(rows);
+        // Act
+        var found = registry.TryGetDefinition(PrototypeNpcBehaviorRegistry.PrototypeMeleePressure, out var def);
+        // Assert
+        Assert.True(found);
+        Assert.NotNull(def);
+        Assert.Equal(100, def.MaxHp);
+        Assert.Equal(8.0, def.AggroRadius);
+        Assert.Equal(16.0, def.LeashRadius);
+        Assert.Equal(15, def.AttackDamage);
+        Assert.Equal(1.5, def.TelegraphWindupSeconds);
+        Assert.Equal("melee_pressure", def.ArchetypeKind);
+        Assert.Equal("Melee Pressure", def.DisplayName);
+    }
+
+    [Fact]
+    public void TryGetDefinition_ShouldReturnTrueAndExpectedMetadata_WhenEliteExists()
+    {
+        // Arrange
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal)
+        {
+            [PrototypeNpcBehaviorRegistry.PrototypeEliteMiniBoss] = EliteRow(),
+        };
+        var registry = CreateRegistryFromRows(rows);
+        // Act
+        var found = registry.TryGetDefinition(PrototypeNpcBehaviorRegistry.PrototypeEliteMiniBoss, out var def);
+        // Assert
+        Assert.True(found);
+        Assert.NotNull(def);
+        Assert.Equal(200, def.MaxHp);
+        Assert.Equal(25, def.AttackDamage);
+        Assert.Equal(2.5, def.TelegraphWindupSeconds);
+    }
+
+    [Fact]
+    public void TryGetDefinition_ShouldReturnFalse_WhenBehaviorIdIsNull()
+    {
+        // Arrange
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal)
+        {
+            [PrototypeNpcBehaviorRegistry.PrototypeMeleePressure] = MeleeRow(),
+        };
+        var registry = CreateRegistryFromRows(rows);
+        // Act
+        var found = registry.TryGetDefinition(null, out var def);
+        // Assert
+        Assert.False(found);
+        Assert.Null(def);
+    }
+
+    [Fact]
+    public void TryGetDefinition_ShouldReturnFalse_WhenIdUnknown()
+    {
+        // Arrange
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal)
+        {
+            [PrototypeNpcBehaviorRegistry.PrototypeMeleePressure] = MeleeRow(),
+        };
+        var registry = CreateRegistryFromRows(rows);
+        // Act
+        var found = registry.TryGetDefinition("not_a_real_behavior", out var def);
+        // Assert
+        Assert.False(found);
+        Assert.Null(def);
+    }
+
+    [Fact]
+    public void TryNormalizeKnown_ShouldReturnTrueAndLowercaseId_WhenInputHasWhitespaceAndMixedCase()
+    {
+        // Arrange
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal)
+        {
+            [PrototypeNpcBehaviorRegistry.PrototypeMeleePressure] = MeleeRow(),
+        };
+        var registry = CreateRegistryFromRows(rows);
+        // Act
+        var found = registry.TryNormalizeKnown("  Prototype_Melee_Pressure  ", out var normalized);
+        // Assert
+        Assert.True(found);
+        Assert.Equal(PrototypeNpcBehaviorRegistry.PrototypeMeleePressure, normalized);
+    }
+
+    [Fact]
+    public void TryNormalizeKnown_ShouldReturnFalse_WhenInputIsNull()
+    {
+        // Arrange
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal)
+        {
+            [PrototypeNpcBehaviorRegistry.PrototypeMeleePressure] = MeleeRow(),
+        };
+        var registry = CreateRegistryFromRows(rows);
+        // Act
+        var found = registry.TryNormalizeKnown(null, out var normalized);
+        // Assert
+        Assert.False(found);
+        Assert.Equal(string.Empty, normalized);
+    }
+
+    [Fact]
+    public void TryNormalizeKnown_ShouldReturnFalse_WhenInputIsWhitespaceOnly()
+    {
+        // Arrange
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal)
+        {
+            [PrototypeNpcBehaviorRegistry.PrototypeMeleePressure] = MeleeRow(),
+        };
+        var registry = CreateRegistryFromRows(rows);
+        // Act
+        var found = registry.TryNormalizeKnown("   ", out var normalized);
+        // Assert
+        Assert.False(found);
+        Assert.Equal(string.Empty, normalized);
+    }
+
+    [Fact]
+    public void TryNormalizeKnown_ShouldReturnFalse_WhenIdNotInCatalog()
+    {
+        // Arrange
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal)
+        {
+            [PrototypeNpcBehaviorRegistry.PrototypeMeleePressure] = MeleeRow(),
+        };
+        var registry = CreateRegistryFromRows(rows);
+        // Act
+        var found = registry.TryNormalizeKnown("prototype_unknown", out var normalized);
+        // Assert
+        Assert.False(found);
+        Assert.Equal("prototype_unknown", normalized);
+    }
+
+    [Fact]
+    public void GetDefinitionsInIdOrder_ShouldListAllRowsOrderedById_WhenMultipleBehaviors()
+    {
+        // Arrange
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal)
+        {
+            [PrototypeNpcBehaviorRegistry.PrototypeRangedControl] = RangedRow(),
+            [PrototypeNpcBehaviorRegistry.PrototypeEliteMiniBoss] = EliteRow(),
+            [PrototypeNpcBehaviorRegistry.PrototypeMeleePressure] = MeleeRow(),
+        };
+        var registry = CreateRegistryFromRows(rows);
+        // Act
+        var list = registry.GetDefinitionsInIdOrder();
+        // Assert
+        Assert.Equal(3, list.Count);
+        Assert.Equal(PrototypeNpcBehaviorRegistry.PrototypeEliteMiniBoss, list[0].Id);
+        Assert.Equal(PrototypeNpcBehaviorRegistry.PrototypeMeleePressure, list[1].Id);
+        Assert.Equal(PrototypeNpcBehaviorRegistry.PrototypeRangedControl, list[2].Id);
+    }
+
+    [Fact]
+    public void TryGetDefinition_ShouldMatchLoaderCatalog_WhenUsingPrototypeFixture()
+    {
+        // Arrange
+        var root = Directory.CreateTempSubdirectory("neon-sprawl-npc-registry-loader-");
+        try
+        {
+            var npcBehaviorsDir = Path.Combine(root.FullName, "content", "npc-behaviors");
+            var schemaDir = Path.Combine(root.FullName, "content", "schemas");
+            Directory.CreateDirectory(npcBehaviorsDir);
+            Directory.CreateDirectory(schemaDir);
+            var schemaPath = Path.Combine(schemaDir, "npc-behavior-def.schema.json");
+            File.Copy(NpcBehaviorCatalogTestPaths.DiscoverRepoNpcBehaviorDefSchemaPath(), schemaPath, overwrite: true);
+            File.Copy(
+                Path.Combine(NpcBehaviorCatalogTestPaths.DiscoverRepoNpcBehaviorsDirectory(), "prototype_npc_behaviors.json"),
+                Path.Combine(npcBehaviorsDir, "prototype_npc_behaviors.json"),
+                overwrite: true);
+            var loaded = NpcBehaviorDefinitionCatalogLoader.Load(npcBehaviorsDir, schemaPath, NullLogger.Instance);
+            var registry = new NpcBehaviorDefinitionRegistry(loaded);
+            // Act
+            var meleeOk = registry.TryGetDefinition(PrototypeNpcBehaviorRegistry.PrototypeMeleePressure, out var melee);
+            var rangedOk = registry.TryGetDefinition(PrototypeNpcBehaviorRegistry.PrototypeRangedControl, out var ranged);
+            var eliteOk = registry.TryGetDefinition(PrototypeNpcBehaviorRegistry.PrototypeEliteMiniBoss, out var elite);
+            var list = registry.GetDefinitionsInIdOrder();
+            // Assert
+            Assert.True(meleeOk);
+            Assert.NotNull(melee);
+            Assert.Equal(100, melee!.MaxHp);
+            Assert.Equal(8.0, melee.AggroRadius);
+            Assert.Equal(16.0, melee.LeashRadius);
+            Assert.Equal(15, melee.AttackDamage);
+            Assert.Equal(1.5, melee.TelegraphWindupSeconds);
+            Assert.True(rangedOk);
+            Assert.NotNull(ranged);
+            Assert.Equal(80, ranged!.MaxHp);
+            Assert.Equal(10.0, ranged.AggroRadius);
+            Assert.Equal(20.0, ranged.LeashRadius);
+            Assert.Equal(12, ranged.AttackDamage);
+            Assert.Equal(2.0, ranged.TelegraphWindupSeconds);
+            Assert.True(eliteOk);
+            Assert.NotNull(elite);
+            Assert.Equal(200, elite!.MaxHp);
+            Assert.Equal(8.0, elite.AggroRadius);
+            Assert.Equal(18.0, elite.LeashRadius);
+            Assert.Equal(25, elite.AttackDamage);
+            Assert.Equal(2.5, elite.TelegraphWindupSeconds);
+            Assert.Equal(3, list.Count);
+            Assert.Equal(PrototypeNpcBehaviorRegistry.PrototypeEliteMiniBoss, list[0].Id);
+            Assert.Equal(PrototypeNpcBehaviorRegistry.PrototypeRangedControl, list[^1].Id);
+        }
+        finally
+        {
+            try
+            {
+                Directory.Delete(root.FullName, recursive: true);
+            }
+            catch (IOException)
+            {
+                // Best-effort: transient lock or race on some hosts; temp dir is unique per run.
+            }
+        }
+    }
+
+    [Fact]
+    public async Task Host_ShouldResolveRegistryFromDi_WhenStartupSucceeds()
+    {
+        // Arrange
+        await using var factory = new InMemoryWebApplicationFactory();
+        using var client = factory.CreateClient();
+        _ = await client.GetAsync("/health");
+        // Act
+        var registry = factory.Services.GetRequiredService<INpcBehaviorDefinitionRegistry>();
+        var meleeFound = registry.TryGetDefinition(PrototypeNpcBehaviorRegistry.PrototypeMeleePressure, out var melee);
+        var unknown = registry.TryGetDefinition("not_a_real_behavior", out var missing);
+        var normalized = registry.TryNormalizeKnown(" Prototype_Ranged_Control ", out var rangedId);
+        var list = registry.GetDefinitionsInIdOrder();
+        // Assert
+        Assert.True(meleeFound);
+        Assert.NotNull(melee);
+        Assert.Equal(100, melee!.MaxHp);
+        Assert.Equal(15, melee.AttackDamage);
+        Assert.False(unknown);
+        Assert.Null(missing);
+        Assert.True(normalized);
+        Assert.Equal(PrototypeNpcBehaviorRegistry.PrototypeRangedControl, rangedId);
+        Assert.Equal(3, list.Count);
+        Assert.Contains(
+            list,
+            b => b.Id == PrototypeNpcBehaviorRegistry.PrototypeEliteMiniBoss && b.MaxHp == 200 && b.AttackDamage == 25);
+    }
+}
diff --git a/server/NeonSprawl.Server/Game/Npc/INpcBehaviorDefinitionRegistry.cs b/server/NeonSprawl.Server/Game/Npc/INpcBehaviorDefinitionRegistry.cs
new file mode 100644
index 0000000..b72582b
--- /dev/null
+++ b/server/NeonSprawl.Server/Game/Npc/INpcBehaviorDefinitionRegistry.cs
@@ -0,0 +1,23 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace NeonSprawl.Server.Game.Npc;
+
+/// <summary>
+/// Read-only access to validated <see cref="NpcBehaviorDefRow"/> entries loaded at startup (<see cref="NpcBehaviorDefinitionCatalog"/>).
+/// </summary>
+/// <remarks>
+/// <para><b>E5.M2 (NPC runtime / instance binding):</b> callers validating behavior ids and resolving aggro/telegraph metadata should depend on this interface
+/// rather than <see cref="NpcBehaviorDefinitionCatalog"/> so behavior defs stay centralized.</para>
+/// <para><b>NEO-90:</b> HTTP/read-model projections should depend on this interface rather than reaching into the catalog.</para>
+/// </remarks>
+public interface INpcBehaviorDefinitionRegistry
+{
+    /// <summary>Attempts to resolve a behavior by stable <c>id</c> (see <c>npc-behavior-def.schema.json</c>). Unknown ids and <c>null</c> return <c>false</c> without throwing.</summary>
+    bool TryGetDefinition(string? behaviorId, [NotNullWhen(true)] out NpcBehaviorDefRow? definition);
+
+    /// <summary>Trims and lowercases <paramref name="rawBehaviorId"/>; returns <c>true</c> when the normalized id exists in the loaded catalog. <c>null</c>, empty, and whitespace return <c>false</c> without throwing.</summary>
+    bool TryNormalizeKnown(string? rawBehaviorId, [NotNullWhen(true)] out string normalized);
+
+    /// <summary>Every loaded definition, ordered by <see cref="NpcBehaviorDefRow.Id"/> (ordinal).</summary>
+    IReadOnlyList<NpcBehaviorDefRow> GetDefinitionsInIdOrder();
+}
diff --git a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogServiceCollectionExtensions.cs b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogServiceCollectionExtensions.cs
index 9f16625..9263535 100644
--- a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogServiceCollectionExtensions.cs
+++ b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogServiceCollectionExtensions.cs
@@ -8,7 +8,7 @@ namespace NeonSprawl.Server.Game.Npc;
 /// <summary>DI registration for the fail-fast NPC behavior catalog (NEO-88).</summary>
 public static class NpcBehaviorCatalogServiceCollectionExtensions
 {
-    /// <summary>Binds <see cref="ContentPathsOptions"/> and registers <see cref="NpcBehaviorDefinitionCatalog"/> as a singleton.</summary>
+    /// <summary>Binds <see cref="ContentPathsOptions"/> and registers <see cref="NpcBehaviorDefinitionCatalog"/> and <see cref="INpcBehaviorDefinitionRegistry"/> as singletons.</summary>
     public static IServiceCollection AddNpcBehaviorDefinitionCatalog(this IServiceCollection services, IConfiguration configuration)
     {
         services.AddOptions<ContentPathsOptions>()
@@ -32,6 +32,9 @@ public static class NpcBehaviorCatalogServiceCollectionExtensions
             return NpcBehaviorDefinitionCatalogLoader.Load(npcBehaviorsDir, schemaPath, logger);
         });
 
+        services.AddSingleton<INpcBehaviorDefinitionRegistry>(sp =>
+            new NpcBehaviorDefinitionRegistry(sp.GetRequiredService<NpcBehaviorDefinitionCatalog>()));
+
         return services;
     }
 }
diff --git a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalog.cs b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalog.cs
index 14d2264..6122d97 100644
--- a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalog.cs
+++ b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalog.cs
@@ -2,7 +2,7 @@ using System.Collections.ObjectModel;
 
 namespace NeonSprawl.Server.Game.Npc;
 
-/// <summary>In-memory NPC behavior catalog loaded at startup (NEO-88). Game callers should use INpcBehaviorDefinitionRegistry (NEO-89).</summary>
+/// <summary>In-memory NPC behavior catalog loaded at startup (NEO-88). Game callers should use <see cref="INpcBehaviorDefinitionRegistry"/>.</summary>
 public sealed class NpcBehaviorDefinitionCatalog(
     string npcBehaviorsDirectory,
     IReadOnlyDictionary<string, NpcBehaviorDefRow> byId,
diff --git a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionRegistry.cs b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionRegistry.cs
new file mode 100644
index 0000000..2ae0b96
--- /dev/null
+++ b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionRegistry.cs
@@ -0,0 +1,55 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace NeonSprawl.Server.Game.Npc;
+
+/// <summary>Adapter over <see cref="NpcBehaviorDefinitionCatalog"/> (NEO-89).</summary>
+public sealed class NpcBehaviorDefinitionRegistry(NpcBehaviorDefinitionCatalog catalog) : INpcBehaviorDefinitionRegistry
+{
+    private readonly IReadOnlyList<NpcBehaviorDefRow> _definitionsInIdOrder = BuildDefinitionsInIdOrder(catalog);
+
+    /// <inheritdoc />
+    public bool TryGetDefinition(string? behaviorId, [NotNullWhen(true)] out NpcBehaviorDefRow? definition)
+    {
+        if (behaviorId is null)
+        {
+            definition = null;
+            return false;
+        }
+
+        return catalog.TryGetBehavior(behaviorId, out definition);
+    }
+
+    /// <inheritdoc />
+    public bool TryNormalizeKnown(string? rawBehaviorId, [NotNullWhen(true)] out string normalized)
+    {
+        if (rawBehaviorId is null)
+        {
+            normalized = string.Empty;
+            return false;
+        }
+
+        normalized = rawBehaviorId.Trim().ToLowerInvariant();
+        if (normalized.Length == 0)
+        {
+            normalized = string.Empty;
+            return false;
+        }
+
+        return catalog.TryGetBehavior(normalized, out _);
+    }
+
+    /// <inheritdoc />
+    public IReadOnlyList<NpcBehaviorDefRow> GetDefinitionsInIdOrder() => _definitionsInIdOrder;
+
+    private static IReadOnlyList<NpcBehaviorDefRow> BuildDefinitionsInIdOrder(NpcBehaviorDefinitionCatalog catalog)
+    {
+        var ids = catalog.ById.Keys.OrderBy(k => k, StringComparer.Ordinal).ToArray();
+        var list = new List<NpcBehaviorDefRow>(ids.Length);
+        foreach (var id in ids)
+        {
+            list.Add(catalog.ById[id]);
+        }
+
+        return list;
+    }
+}
diff --git a/server/NeonSprawl.Server/Game/Npc/PrototypeNpcBehaviorRegistry.cs b/server/NeonSprawl.Server/Game/Npc/PrototypeNpcBehaviorRegistry.cs
new file mode 100644
index 0000000..62d3b9e
--- /dev/null
+++ b/server/NeonSprawl.Server/Game/Npc/PrototypeNpcBehaviorRegistry.cs
@@ -0,0 +1,9 @@
+namespace NeonSprawl.Server.Game.Npc;
+
+/// <summary>Stable prototype NPC behavior id constants for tests and fixtures (NEO-89). Validation and lookup use <see cref="INpcBehaviorDefinitionRegistry"/>.</summary>
+public static class PrototypeNpcBehaviorRegistry
+{
+    public const string PrototypeMeleePressure = "prototype_melee_pressure";
+    public const string PrototypeRangedControl = "prototype_ranged_control";
+    public const string PrototypeEliteMiniBoss = "prototype_elite_mini_boss";
+}