diff --git a/changelog.d/fixes/7845-log-detail-structured-error.md b/changelog.d/fixes/7845-log-detail-structured-error.md
new file mode 100644
index 0000000000..909c9ff960
--- /dev/null
+++ b/changelog.d/fixes/7845-log-detail-structured-error.md
@@ -0,0 +1 @@
+- fix(dashboard): Request Logs detail modal no longer crashes when the persisted error is a structured object (#7845)
diff --git a/src/shared/components/RequestLoggerDetail.tsx b/src/shared/components/RequestLoggerDetail.tsx
index 30dc8b5091..01647eb252 100644
--- a/src/shared/components/RequestLoggerDetail.tsx
+++ b/src/shared/components/RequestLoggerDetail.tsx
@@ -7,6 +7,7 @@ import {
   getProtocolColor,
 } from "@/shared/constants/colors";
 import { formatDuration, formatApiKeyLabel, maskAccount } from "@/shared/utils/formatting";
+import { formatErrorForDisplay } from "@/shared/utils/formatting";
 
 // ─── Payload Code Block ─────────────────────────────────────────────────────
 
@@ -617,8 +618,8 @@ export default function RequestLoggerDetail({
               <div className="text-[10px] text-red-600 dark:text-red-400 uppercase tracking-wider mb-1 font-bold">
                 Error
               </div>
-              <div className="text-sm text-red-600 dark:text-red-300 font-mono">
-                {detail?.error || log.error}
+              <div className="text-sm text-red-600 dark:text-red-300 font-mono whitespace-pre-wrap break-words">
+                {formatErrorForDisplay(detail?.error || log.error)}
               </div>
             </div>
           )}
diff --git a/src/shared/utils/formatting.ts b/src/shared/utils/formatting.ts
index 37957d4833..100321d897 100644
--- a/src/shared/utils/formatting.ts
+++ b/src/shared/utils/formatting.ts
@@ -181,3 +181,20 @@ export function formatResetCountdown(resetAt: string | number | null | undefined
   if (minutes > 0) return `${minutes}m ${seconds}s`;
   return `${seconds}s`;
 }
+
+/**
+ * Coerces a persisted log `error` field into safe display text. It is
+ * legitimate for this field to be a structured object (e.g. `{ code,
+ * message }`) — only the RENDER needs to be a string, never the persisted
+ * artifact itself. Used by RequestLoggerDetail to avoid React error #31
+ * ("Objects are not valid as a React child") when rendering it. See #7845.
+ */
+export function formatErrorForDisplay(err: unknown): string | null {
+  if (err == null) return null;
+  if (typeof err === "string") return err;
+  try {
+    return JSON.stringify(err, null, 2);
+  } catch {
+    return String(err);
+  }
+}
diff --git a/tests/unit/ui/issue-7845-log-detail-structured-error.test.tsx b/tests/unit/ui/issue-7845-log-detail-structured-error.test.tsx
new file mode 100644
index 0000000000..15405507d4
--- /dev/null
+++ b/tests/unit/ui/issue-7845-log-detail-structured-error.test.tsx
@@ -0,0 +1,117 @@
+// @vitest-environment jsdom
+/**
+ * TDD regression for #7845: opening the detail modal for a failed
+ * /dashboard/logs entry crashes the dashboard (React error #31 —
+ * "Objects are not valid as a React child") when the persisted artifact's
+ * `error` field is a structured object (e.g. `{ code, message }`) instead of
+ * a plain string.
+ *
+ * Root cause: `RequestLoggerDetail` rendered `{detail?.error || log.error}`
+ * directly as a React child. The list summary keeps `error_summary` as a
+ * string, but `/api/logs/{id}` returns the persisted structured `error`
+ * object for detail view — React throws when that object hits the child
+ * position (error #31).
+ *
+ * Fix: coerce any non-string `error` payload to a formatted JSON string
+ * before rendering, while leaving plain string errors rendered verbatim
+ * (no added JSON quoting).
+ */
+import React from "react";
+import { act } from "react";
+import { createRoot, type Root } from "react-dom/client";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+
+const RequestLoggerDetail = (
+  await import("../../../src/shared/components/RequestLoggerDetail.tsx")
+).default;
+
+let container: HTMLElement;
+let root: Root;
+
+function baseLog(overrides: Record<string, unknown> = {}) {
+  return {
+    id: "log-1",
+    status: 500,
+    method: "POST",
+    path: "/v1/chat/completions",
+    model: "gpt-test",
+    provider: "openai",
+    timestamp: new Date().toISOString(),
+    duration: 42,
+    tokens: { in: 1, out: 2 },
+    ...overrides,
+  };
+}
+
+const noop = () => {};
+
+beforeEach(() => {
+  container = document.createElement("div");
+  document.body.appendChild(container);
+  root = createRoot(container);
+});
+
+afterEach(async () => {
+  if (root) {
+    await act(async () => {
+      root.unmount();
+    });
+  }
+  container?.remove();
+});
+
+describe("RequestLoggerDetail structured error rendering (#7845)", () => {
+  it("renders a structured object error without throwing, showing its content in the DOM", async () => {
+    const structuredError = {
+      code: "codex_ws_provider_required",
+      message: "Responses WebSocket bridge only supports Codex models, got proxy",
+    };
+    const log = baseLog({ error: structuredError });
+    const detail = { ...log, error: structuredError };
+
+    let renderError: unknown = null;
+    await act(async () => {
+      try {
+        root.render(
+          <RequestLoggerDetail
+            log={log}
+            detail={detail}
+            loading={false}
+            debugEnabled={false}
+            onClose={noop}
+            onCopy={async () => true}
+          />
+        );
+      } catch (err) {
+        renderError = err;
+      }
+    });
+
+    expect(renderError).toBeNull();
+    expect(container.textContent).toContain("codex_ws_provider_required");
+    expect(container.textContent).toContain(
+      "Responses WebSocket bridge only supports Codex models, got proxy"
+    );
+  });
+
+  it("keeps rendering a plain string error verbatim, with no added JSON quoting", async () => {
+    const log = baseLog({ error: "upstream timeout" });
+    const detail = { ...log, error: "upstream timeout" };
+
+    await act(async () => {
+      root.render(
+        <RequestLoggerDetail
+          log={log}
+          detail={detail}
+          loading={false}
+          debugEnabled={false}
+          onClose={noop}
+          onCopy={async () => true}
+        />
+      );
+    });
+
+    expect(container.textContent).toContain("upstream timeout");
+    expect(container.textContent).not.toContain('"upstream timeout"');
+  });
+});