diff --git a/apps/cloud/src/api/error-response.ts b/apps/cloud/src/api/error-response.ts
index c122371d4..a076c93ba 100644
--- a/apps/cloud/src/api/error-response.ts
+++ b/apps/cloud/src/api/error-response.ts
@@ -48,11 +48,26 @@ const toHttpResponseError = (error: unknown): HttpResponseError => {
       });
 };
 
+// Sentry's `captureException` can't extract a real Error from an Effect
+// `Cause` — it logs a `'CauseImpl' captured as exception` warning. Squash
+// to a plain value and stash the pretty-printed cause as an extra.
+const captureSentryError = (error: unknown): void => {
+  if (Cause.isCause(error)) {
+    const pretty = Cause.pretty(error);
+    Sentry.captureException(Cause.squash(error), (scope) => {
+      scope.setExtra("cause", pretty);
+      return scope;
+    });
+  } else {
+    Sentry.captureException(error);
+  }
+};
+
 export const isServerError = (error: unknown): boolean => toHttpResponseError(error).status >= 500;
 
 export const toErrorResponse = (error: unknown): Response => {
   const mapped = toHttpResponseError(error);
-  if (mapped.status >= 500) Sentry.captureException(error);
+  if (mapped.status >= 500) captureSentryError(error);
   return Response.json({ error: mapped.message, code: mapped.code }, { status: mapped.status });
 };
 
@@ -61,9 +76,9 @@ export const toErrorServerResponse = (error: unknown): HttpServerResponse.HttpSe
   if (mapped.status >= 500) {
     console.error(
       "[api] toErrorServerResponse error:",
-      error instanceof Error ? error.stack : error,
+      Cause.isCause(error) ? Cause.pretty(error) : error instanceof Error ? error.stack : error,
     );
-    Sentry.captureException(error);
+    captureSentryError(error);
   }
   return HttpServerResponse.jsonUnsafe(
     { error: mapped.message, code: mapped.code },
diff --git a/apps/cloud/src/mcp-session.ts b/apps/cloud/src/mcp-session.ts
index 26a457952..92163f408 100644
--- a/apps/cloud/src/mcp-session.ts
+++ b/apps/cloud/src/mcp-session.ts
@@ -4,7 +4,7 @@
 
 import { DurableObject, env } from "cloudflare:workers";
 import { createTraceState } from "@opentelemetry/api";
-import { Data, Effect, Layer } from "effect";
+import { Cause, Data, Effect, Layer } from "effect";
 import * as OtelTracer from "@effect/opentelemetry/Tracer";
 import type * as Tracer from "effect/Tracer";
 import * as Sentry from "@sentry/cloudflare";
@@ -624,8 +624,12 @@ export class McpSessionDO extends DurableObject {
     }).pipe(
       Effect.catchCause((cause) =>
         Effect.sync(() => {
-          console.error("[mcp-session] handleRequest error:", cause);
-          Sentry.captureException(cause);
+          const pretty = Cause.pretty(cause);
+          console.error("[mcp-session] handleRequest error:", pretty);
+          Sentry.captureException(Cause.squash(cause), (scope) => {
+            scope.setExtra("cause", pretty);
+            return scope;
+          });
           return jsonRpcError(500, -32603, "Internal error");
         }),
       ),
diff --git a/apps/cloud/src/mcp.ts b/apps/cloud/src/mcp.ts
index 958fed84f..3d69dc1a3 100644
--- a/apps/cloud/src/mcp.ts
+++ b/apps/cloud/src/mcp.ts
@@ -17,7 +17,7 @@
 import { env } from "cloudflare:workers";
 import { HttpEffect, HttpServerRequest, HttpServerResponse } from "effect/unstable/http";
 import * as Sentry from "@sentry/cloudflare";
-import { Context, Effect, Layer, Option, Schema } from "effect";
+import { Cause, Context, Effect, Layer, Option, Schema } from "effect";
 
 import { createCachedRemoteJWKSet } from "./jwks-cache";
 import { TelemetryLive } from "./services/telemetry";
@@ -697,8 +697,12 @@ export const mcpApp: Effect.Effect<
   Effect.withSpan("mcp.request"),
   Effect.catchCause((cause) =>
     Effect.sync(() => {
-      console.error("[mcp] request failed:", cause);
-      Sentry.captureException(cause);
+      const pretty = Cause.pretty(cause);
+      console.error("[mcp] request failed:", pretty);
+      Sentry.captureException(Cause.squash(cause), (scope) => {
+        scope.setExtra("cause", pretty);
+        return scope;
+      });
       return jsonRpcError(500, -32603, "Internal server error");
     }),
   ),