feat(mcp): Add MCP server tracing

.changeset/add-mcp-server-tracing.md

@@ -0,0 +1,5 @@
+---
+"braintrust": minor
+---
+
+feat(mcp): Add MCP server tracing

e2e/config/pr-comment-scenarios.json

@@ -592,6 +592,29 @@
       }
     ]
   },
+  {
+    "scenarioDirName": "mcp-instrumentation",
+    "label": "MCP Instrumentation",
+    "metadataScenario": "mcp-instrumentation",
+    "variants": [
+      {
+        "variantKey": "mcp-sdk-v1",
+        "label": "sdk v1 pinned"
+      },
+      {
+        "variantKey": "mcp-sdk-v1-latest",
+        "label": "sdk v1 latest"
+      },
+      {
+        "variantKey": "mcp-server-v2",
+        "label": "server v2 pinned"
+      },
+      {
+        "variantKey": "mcp-server-v2-latest",
+        "label": "server v2 latest"
+      }
+    ]
+  },
   {
     "scenarioDirName": "typesafe-instrumentation",
     "label": "TypeSafe Instrumentation",

e2e/helpers/normalize.test.ts

@@ -2,6 +2,33 @@ import { describe, expect, test } from "vitest";
 import { normalizeForSnapshot } from "./normalize";
 
 describe("normalizeForSnapshot", () => {
+  test.each([0, 0.1, 1.2])(
+    "normalizes tool wall time of %s seconds",
+    (seconds) => {
+      expect(
+        normalizeForSnapshot({
+          output: {
+            structuredContent: {
+              exit_code: 0,
+              output: "pi_tool_ok",
+              truncated: false,
+              wall_time_seconds: seconds,
+            },
+          },
+        }),
+      ).toEqual({
+        output: {
+          structuredContent: {
+            exit_code: 0,
+            output: "pi_tool_ok",
+            truncated: false,
+            wall_time_seconds: 0,
+          },
+        },
+      });
+    },
+  );
+
   test("normalizes a foreign repository path ending at a workspace directory", () => {
     expect(
       normalizeForSnapshot(

e2e/helpers/normalize.ts

@@ -75,6 +75,7 @@ const ZERO_NUMBER_KEYS = new Set([
   "duration",
   "github_copilot.context_window.current",
   "time_to_first_token",
+  "wall_time_seconds",
 ]);
 const XACT_VERSION_KEYS = new Set([
   "currentVersion",