diff --git a/apps/server/src/mcp/McpHttpServer.test.ts b/apps/server/src/mcp/McpHttpServer.test.ts
index 210bb7e5ad8ad567ee676232735fc423a95a1140..f550396c660218b7b561f56a2220c1e574051ec5 100644
--- a/apps/server/src/mcp/McpHttpServer.test.ts
+++ b/apps/server/src/mcp/McpHttpServer.test.ts
@@ -49,6 +49,62 @@ it("normalizes empty successful notification responses to accepted", () => {
   expect(resultResponse.status).toBe(200);
 });
 
+it.effect("returns bounded structural preview snapshot failures", () =>
+  Effect.scoped(
+    Effect.gen(function* () {
+      const server = yield* McpServer.McpServer;
+      const broker = yield* PreviewAutomationBroker.PreviewAutomationBroker;
+      const requests = yield* broker.connect({
+        clientId: "mcp-failure-client",
+        environmentId,
+        threadId,
+        tabId,
+        visible: true,
+        supportsAutomation: true,
+        focusedAt: "2026-06-11T00:00:00.000Z",
+      });
+      yield* Stream.runForEach(requests, (request) =>
+        broker.respond({
+          requestId: request.requestId,
+          ok: false,
+          error: {
+            _tag: "PreviewAutomationExecutionError",
+            message: "sensitive renderer failure",
+            detail: { consoleOutput: "sensitive browser output" },
+          },
+        }),
+      ).pipe(Effect.forkScoped);
+      yield* Effect.yieldNow;
+      yield* broker.reportOwner({
+        clientId: "mcp-failure-client",
+        environmentId,
+        threadId,
+        tabId,
+        visible: true,
+        supportsAutomation: true,
+        focusedAt: "2026-06-11T00:00:00.000Z",
+      });
+
+      const snapshot = yield* server
+        .callTool({ name: "preview_snapshot", arguments: {} })
+        .pipe(
+          Effect.provideService(McpInvocationContext.McpInvocationContext, invocation),
+          Effect.provideService(McpSchema.McpServerClient, client),
+        );
+
+      expect(snapshot.isError).toBe(true);
+      expect(snapshot.content).toEqual([{ type: "text", text: "Preview snapshot failed." }]);
+      expect(snapshot.structuredContent).toEqual({
+        error: {
+          _tag: "PreviewAutomationExecutionError",
+          operation: "snapshot",
+          failureCount: 1,
+        },
+      });
+    }),
+  ).pipe(Effect.provide(TestLayer)),
+);
+
 it.effect("terminates HTTP MCP sessions with DELETE", () =>
   Effect.scoped(
     Effect.gen(function* () {
diff --git a/apps/server/src/mcp/McpHttpServer.ts b/apps/server/src/mcp/McpHttpServer.ts
index 6cde2017a9e415be2fab024601444fca738a42be..e95662a30f897d2808b52084a599489e4b600916 100644
--- a/apps/server/src/mcp/McpHttpServer.ts
+++ b/apps/server/src/mcp/McpHttpServer.ts
@@ -88,6 +88,37 @@ const McpAuthMiddlewareLive = HttpRouter.middleware<{
   provides: McpInvocationContext.McpInvocationContext;
 }>()(makeMcpAuthMiddleware).layer;
 
+const previewSnapshotFailure = <E>(cause: Cause.Cause<E>) => {
+  if (Cause.hasInterrupts(cause) || cause.reasons.some(Cause.isDieReason)) {
+    return Effect.failCause(cause).pipe(Effect.orDie);
+  }
+  const failures = cause.reasons.filter(Cause.isFailReason);
+  const firstFailure = failures[0]?.error;
+  const errorTag =
+    typeof firstFailure === "object" &&
+    firstFailure !== null &&
+    "_tag" in firstFailure &&
+    typeof firstFailure._tag === "string"
+      ? firstFailure._tag
+      : "PreviewSnapshotError";
+  const result = new McpSchema.CallToolResult({
+    isError: true,
+    structuredContent: {
+      error: {
+        _tag: errorTag,
+        operation: "snapshot",
+        failureCount: failures.length,
+      },
+    },
+    content: [{ type: "text", text: "Preview snapshot failed." }],
+  });
+  return Effect.logWarning("preview snapshot failed", {
+    operation: "snapshot",
+    errorTag,
+    failureCount: failures.length,
+  }).pipe(Effect.as(result));
+};
+
 const registerPreviewSnapshot = Effect.fn("McpHttpServer.registerPreviewSnapshot")(function* () {
   const server = yield* McpServer.McpServer;
   const broker = yield* PreviewAutomationBroker.PreviewAutomationBroker;
@@ -122,12 +153,8 @@ const registerPreviewSnapshot = Effect.fn("McpHttpServer.registerPreviewSnapshot
           Effect.flatMap(Effect.fromOption),
           Effect.provideService(PreviewAutomationBroker.PreviewAutomationBroker, broker),
           Effect.provideService(McpInvocationContext.McpInvocationContext, invocation),
-          Effect.matchCause({
-            onFailure: (cause) =>
-              new McpSchema.CallToolResult({
-                isError: true,
-                content: [{ type: "text", text: Cause.pretty(cause) }],
-              }),
+          Effect.matchCauseEffect({
+            onFailure: previewSnapshotFailure,
             onSuccess: ({ encodedResult }) => {
               const snapshot = encodedResult as {
                 readonly screenshot: {
@@ -147,18 +174,20 @@ const registerPreviewSnapshot = Effect.fn("McpHttpServer.registerPreviewSnapshot
                   height: screenshot.height,
                 },
               };
-              return new McpSchema.CallToolResult({
-                isError: false,
-                structuredContent: metadata,
-                content: [
-                  { type: "text", text: JSON.stringify(metadata) },
-                  {
-                    type: "image",
-                    data: new Uint8Array(Buffer.from(screenshot.data, "base64")),
-                    mimeType: screenshot.mimeType,
-                  },
-                ],
-              });
+              return Effect.succeed(
+                new McpSchema.CallToolResult({
+                  isError: false,
+                  structuredContent: metadata,
+                  content: [
+                    { type: "text", text: JSON.stringify(metadata) },
+                    {
+                      type: "image",
+                      data: new Uint8Array(Buffer.from(screenshot.data, "base64")),
+                      mimeType: screenshot.mimeType,
+                    },
+                  ],
+                }),
+              );
             },
           }),
         );