refactor(audience-sdk): introduce ContextKeys and GameLaunchPropertyKeys

Names the per-event context dictionary keys and the auto-fired game_launch property keys, and routes
DeviceCollector's twelve truncation sites through Constants.MaxFieldLength so the 256-char cap reads
as a contract.

- Constants.cs: adds ContextKeys (UserAgent, Timezone, Locale, Screen) and GameLaunchPropertyKeys
  (Platform, Version, BuildGuid, UnityVersion, OsFamily, DeviceModel, Gpu, GpuVendor, Cpu, CpuCores,
  RamMb, ScreenDpi, DistributionPlatform).
- DeviceCollector.cs: CollectContext writes ContextKeys; CollectGameLaunchProperties writes
  GameLaunchPropertyKeys; truncation calls use Constants.MaxFieldLength.
- ImmutableAudience.cs: distribution-platform overlay on game_launch reads
  GameLaunchPropertyKeys.DistributionPlatform.

Author: ImmutableJeffrey

src/Packages/Audience/Runtime/Core/Constants.cs

@@ -62,6 +62,33 @@ internal static class MessageTypes
         internal const string Alias = "alias";
     }
 
+    // Property keys for the auto-fired game_launch event.
+    internal static class GameLaunchPropertyKeys
+    {
+        internal const string Platform = "platform";
+        internal const string Version = "version";
+        internal const string BuildGuid = "buildGuid";
+        internal const string UnityVersion = "unityVersion";
+        internal const string OsFamily = "osFamily";
+        internal const string DeviceModel = "deviceModel";
+        internal const string Gpu = "gpu";
+        internal const string GpuVendor = "gpuVendor";
+        internal const string Cpu = "cpu";
+        internal const string CpuCores = "cpuCores";
+        internal const string RamMb = "ramMb";
+        internal const string ScreenDpi = "screenDpi";
+        internal const string DistributionPlatform = "distributionPlatform";
+    }
+
+    // Keys merged into every event's context dictionary.
+    internal static class ContextKeys
+    {
+        internal const string UserAgent = "userAgent";
+        internal const string Timezone = "timezone";
+        internal const string Locale = "locale";
+        internal const string Screen = "screen";
+    }
+
     // JSON keys for the consent-sync PUT body.
     internal static class ConsentBodyFields
     {

src/Packages/Audience/Runtime/ImmutableAudience.cs

@@ -1016,7 +1016,7 @@ private static void FireGameLaunch(AudienceConfig config, ConsentLevel consentAt
 
             // Config-supplied distributionPlatform overrides the provider value.
             if (config.DistributionPlatform != null)
-                properties["distributionPlatform"] = config.DistributionPlatform;
+                properties[GameLaunchPropertyKeys.DistributionPlatform] = config.DistributionPlatform;
 
             // No sessionId on game_launch per Event Reference. Pipeline correlates
             // via eventTimestamp with the session_start that fires just before.

src/Packages/Audience/Runtime/Unity/DeviceCollector.cs

@@ -14,17 +14,17 @@ internal static Dictionary<string, object> CollectContext()
             // 256-char cap mirrors Web SDK's identifier truncation.
             var ctx = new Dictionary<string, object>
             {
-                ["userAgent"] = Truncate(SystemInfo.operatingSystem, 256),
+                [ContextKeys.UserAgent] = Truncate(SystemInfo.operatingSystem, Constants.MaxFieldLength),
             };
 
             var timezone = SafeTimezone();
-            if (timezone != null) ctx["timezone"] = Truncate(timezone, 256);
+            if (timezone != null) ctx[ContextKeys.Timezone] = Truncate(timezone, Constants.MaxFieldLength);
 
             var locale = LocaleString();
-            if (locale != null) ctx["locale"] = Truncate(locale, 256);
+            if (locale != null) ctx[ContextKeys.Locale] = Truncate(locale, Constants.MaxFieldLength);
 
             var screen = TryResolveScreenString();
-            if (screen != null) ctx["screen"] = Truncate(screen, 256);
+            if (screen != null) ctx[ContextKeys.Screen] = Truncate(screen, Constants.MaxFieldLength);
 
             return ctx;
         }
@@ -49,22 +49,22 @@ internal static Dictionary<string, object> CollectGameLaunchProperties()
         {
             var props = new Dictionary<string, object>
             {
-                ["platform"] = Application.platform.ToString(),
-                ["version"] = Truncate(Application.version, 256),
-                ["buildGuid"] = Truncate(Application.buildGUID, 256),
-                ["unityVersion"] = Truncate(Application.unityVersion, 256),
-                ["osFamily"] = SystemInfo.operatingSystemFamily.ToString(),
-                ["deviceModel"] = Truncate(SystemInfo.deviceModel, 256),
-                ["gpu"] = Truncate(SystemInfo.graphicsDeviceName, 256),
-                ["gpuVendor"] = Truncate(SystemInfo.graphicsDeviceVendor, 256),
-                ["cpu"] = Truncate(SystemInfo.processorType, 256),
-                ["cpuCores"] = SystemInfo.processorCount,
-                ["ramMb"] = SystemInfo.systemMemorySize,
+                [GameLaunchPropertyKeys.Platform] = Application.platform.ToString(),
+                [GameLaunchPropertyKeys.Version] = Truncate(Application.version, Constants.MaxFieldLength),
+                [GameLaunchPropertyKeys.BuildGuid] = Truncate(Application.buildGUID, Constants.MaxFieldLength),
+                [GameLaunchPropertyKeys.UnityVersion] = Truncate(Application.unityVersion, Constants.MaxFieldLength),
+                [GameLaunchPropertyKeys.OsFamily] = SystemInfo.operatingSystemFamily.ToString(),
+                [GameLaunchPropertyKeys.DeviceModel] = Truncate(SystemInfo.deviceModel, Constants.MaxFieldLength),
+                [GameLaunchPropertyKeys.Gpu] = Truncate(SystemInfo.graphicsDeviceName, Constants.MaxFieldLength),
+                [GameLaunchPropertyKeys.GpuVendor] = Truncate(SystemInfo.graphicsDeviceVendor, Constants.MaxFieldLength),
+                [GameLaunchPropertyKeys.Cpu] = Truncate(SystemInfo.processorType, Constants.MaxFieldLength),
+                [GameLaunchPropertyKeys.CpuCores] = SystemInfo.processorCount,
+                [GameLaunchPropertyKeys.RamMb] = SystemInfo.systemMemorySize,
             };
 
             // Screen.dpi can be 0 on some Linux WMs.
             var dpi = (int)Screen.dpi;
-            if (dpi > 0) props["screenDpi"] = dpi;
+            if (dpi > 0) props[GameLaunchPropertyKeys.ScreenDpi] = dpi;
 
             return props;
         }