diff --git a/apps/api/src/app.ts b/apps/api/src/app.ts
index 8cfbd91..fa61f56 100644
--- a/apps/api/src/app.ts
+++ b/apps/api/src/app.ts
@@ -1,5 +1,5 @@
 import { randomUUID } from "node:crypto";
-import { ORPCError, onError } from "@orpc/server";
+import { ORPCError, onError, ValidationError } from "@orpc/server";
 import { RPCHandler } from "@orpc/server/fetch";
 import type {
   AgentRuntime,
@@ -1048,7 +1048,18 @@ function sessionHeaders(request: Request) {
  * "fetch failed" and keep the host and errno one level down.
  */
 export function logUnexpectedRpcError(error: unknown, path: readonly string[]): void {
-  if (error instanceof ORPCError) return;
   const where = `rpc ${path.join("/")} failed`;
+  if (error instanceof ORPCError) {
+    // A handler result that breaks its output contract is a server bug, not a chosen error.
+    if (error.code !== "INTERNAL_SERVER_ERROR" || !(error.cause instanceof ValidationError)) return;
+    const issues = error.cause.issues.map((issue) => ({
+      path: (issue.path ?? [])
+        .map((segment) => (typeof segment === "object" ? segment.key : segment))
+        .join("."),
+      problem: issue.message,
+    }));
+    getLogger().error(where, error, { issues });
+    return;
+  }
   getLogger().error(where, error);
 }
diff --git a/apps/api/src/log-unexpected-rpc-error.test.ts b/apps/api/src/log-unexpected-rpc-error.test.ts
index 2e154cf..417077f 100644
--- a/apps/api/src/log-unexpected-rpc-error.test.ts
+++ b/apps/api/src/log-unexpected-rpc-error.test.ts
@@ -1,4 +1,4 @@
-import { ORPCError } from "@orpc/server";
+import { ORPCError, ValidationError } from "@orpc/server";
 import { createLogger, createTestSink, installLogger } from "@rakazo/logging";
 import { afterEach, describe, expect, it } from "vitest";
 import { logUnexpectedRpcError } from "./app.js";
@@ -20,6 +20,28 @@ describe("logUnexpectedRpcError", () => {
     expect(sink.events).toEqual([]);
   });
 
+  it("names the procedure and the fields when a result breaks its output contract", () => {
+    const sink = createTestSink();
+    installLogger(createLogger({ service: "rakazo-api", sinks: [sink] }));
+    const error = new ORPCError("INTERNAL_SERVER_ERROR", {
+      message: "Output validation failed",
+      cause: new ValidationError({
+        message: "Output validation failed",
+        issues: [{ message: "Expected string", path: ["items", 0, { key: "title" }] }],
+        data: { items: [{ title: null, body: "private" }] },
+      }),
+    });
+
+    logUnexpectedRpcError(error, ["inbox", "list"]);
+
+    expect(sink.events).toHaveLength(1);
+    expect(sink.events[0]).toMatchObject({
+      message: "rpc inbox/list failed",
+      issues: [{ path: "items.0.title", problem: "Expected string" }],
+    });
+    expect(JSON.stringify(sink.events[0])).not.toContain("private");
+  });
+
   it("names the procedure and every cause behind an opaque failure", () => {
     const sink = createTestSink();
     installLogger(createLogger({ service: "rakazo-api", sinks: [sink] }));