fix(mcp): Harden profile detail fallbacks

Infer transaction profile sample timestamp units from the timestamp magnitude instead of the duration delta so missing relative bounds do not explode short nanosecond profiles. Add regressions for both epoch-second samples and sub-millisecond nanosecond samples.

Also remove the unused requireSlug branch from resolveProjectContext to keep the profile detail helper aligned with its actual call sites.

Co-Authored-By: Codex GPT-5 <noreply@openai.com>

Author: dcramer

packages/mcp-core/src/tools/get-profile-details.ts

@@ -124,15 +124,13 @@ async function resolveProjectContext(
   projectSlugOrId: string | number,
   options: {
     requireNumericId?: boolean;
-    requireSlug?: boolean;
   } = {},
 ): Promise<{ projectId: string | number; projectSlug: string }> {
   const requireNumericId = options.requireNumericId ?? false;
-  const requireSlug = options.requireSlug ?? false;
   const isNumericProject =
     typeof projectSlugOrId === "number" || isNumericId(String(projectSlugOrId));
 
-  if (!isNumericProject && !requireNumericId && !requireSlug) {
+  if (!isNumericProject && !requireNumericId) {
     return {
       projectId: projectSlugOrId,
       projectSlug: String(projectSlugOrId),

packages/mcp-core/src/tools/profile/formatter.test.ts

@@ -511,6 +511,54 @@ describe("formatter", () => {
       expect(output).toContain("| `app_handler` | app.py:99 | 1 | User Code |");
       expect(output).not.toContain("`library_0`");
     });
+
+    it("falls back to epoch-second sample timestamps when relative bounds are missing", () => {
+      const profile = createMockTransactionProfile();
+
+      if (profile.transaction) {
+        profile.transaction.relative_start_ns = undefined;
+        profile.transaction.relative_end_ns = undefined;
+      }
+
+      profile.profile.samples = [
+        { stack_id: 0, thread_id: "1", timestamp: 1710958503.629 },
+        { stack_id: 1, thread_id: "1", timestamp: 1710958503.679 },
+        { stack_id: 1, thread_id: "1", timestamp: 1710958503.729 },
+      ];
+
+      const output = formatTransactionProfileAnalysis(profile, {
+        focusOnUserCode: true,
+        profileUrl:
+          "https://sentry-mcp-evals.sentry.io/explore/profiling/profile/backend/cfe78a5c892d4a64a962d837673398d2/flamegraph/",
+        projectSlug: "backend",
+      });
+
+      expect(output).toContain("- **Duration**: 100ms");
+    });
+
+    it("preserves nanosecond sample durations under 1ms when relative bounds are missing", () => {
+      const profile = createMockTransactionProfile();
+
+      if (profile.transaction) {
+        profile.transaction.relative_start_ns = undefined;
+        profile.transaction.relative_end_ns = undefined;
+      }
+
+      profile.profile.samples = [
+        { stack_id: 0, thread_id: "1", timestamp: 0 },
+        { stack_id: 1, thread_id: "1", timestamp: 250_000 },
+        { stack_id: 1, thread_id: "1", timestamp: 500_000 },
+      ];
+
+      const output = formatTransactionProfileAnalysis(profile, {
+        focusOnUserCode: true,
+        profileUrl:
+          "https://sentry-mcp-evals.sentry.io/explore/profiling/profile/backend/cfe78a5c892d4a64a962d837673398d2/flamegraph/",
+        projectSlug: "backend",
+      });
+
+      expect(output).toContain("- **Duration**: 500µs");
+    });
   });
 
   describe("edge cases", () => {

packages/mcp-core/src/tools/profile/formatter.ts

@@ -692,7 +692,33 @@ function getTransactionProfileDurationNs(
     return null;
   }
 
-  return duration < 1_000_000 ? Math.round(duration * 1_000_000_000) : duration;
+  const firstTimestampScale = inferSampleTimestampNsScale(timestamps[0]!);
+  const lastTimestampScale = inferSampleTimestampNsScale(
+    timestamps[timestamps.length - 1]!,
+  );
+
+  if (firstTimestampScale && firstTimestampScale === lastTimestampScale) {
+    return Math.round(duration * firstTimestampScale);
+  }
+
+  return Math.round(duration);
+}
+
+function inferSampleTimestampNsScale(timestamp: number): number | null {
+  const absoluteTimestamp = Math.abs(timestamp);
+
+  // Older transaction profile payloads use absolute epoch timestamps.
+  if (absoluteTimestamp >= 1e8 && absoluteTimestamp < 1e11) {
+    return 1_000_000_000;
+  }
+  if (absoluteTimestamp >= 1e11 && absoluteTimestamp < 1e14) {
+    return 1_000_000;
+  }
+  if (absoluteTimestamp >= 1e14 && absoluteTimestamp < 1e17) {
+    return 1_000;
+  }
+
+  return null;
 }
 
 function formatDeviceSummary(profile: TransactionProfile): string | null {