diff --git a/packages/cli/package.json b/packages/cli/package.json
index 9d4c98e55..b0609d3c7 100644
--- a/packages/cli/package.json
+++ b/packages/cli/package.json
@@ -29,7 +29,7 @@
     "dev": "tsx src/index.ts",
     "test": "vitest run",
     "test:watch": "vitest",
-    "typecheck": "pnpm --filter @composio/ao-cli^... build && tsc --noEmit",
+    "typecheck": "tsc --noEmit",
     "clean": "rm -rf dist"
   },
   "dependencies": {
diff --git a/packages/web/package.json b/packages/web/package.json
index 59e0a6306..962df764c 100644
--- a/packages/web/package.json
+++ b/packages/web/package.json
@@ -19,7 +19,7 @@
     "build": "next build && tsc -p tsconfig.server.json",
     "start": "next start",
     "start:all": "node dist-server/start-all.js",
-    "typecheck": "pnpm --filter @composio/ao-web^... build && tsc --noEmit",
+    "typecheck": "tsc --noEmit",
     "test": "vitest run",
     "test:watch": "vitest",
     "clean": "rm -rf .next dist-server",
diff --git a/packages/web/src/app/error.test.tsx b/packages/web/src/app/error.test.tsx
new file mode 100644
index 000000000..5e120196f
--- /dev/null
+++ b/packages/web/src/app/error.test.tsx
@@ -0,0 +1,33 @@
+import { fireEvent, render, screen } from "@testing-library/react";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const refresh = vi.fn();
+
+vi.mock("next/navigation", () => ({
+  useRouter: () => ({ refresh }),
+}));
+
+import ErrorPage from "./error";
+
+describe("Route error boundary", () => {
+  beforeEach(() => {
+    vi.spyOn(console, "error").mockImplementation(() => {});
+  });
+
+  it("retries with reset and router refresh", () => {
+    const reset = vi.fn();
+
+    render(<ErrorPage error={new Error("boom")} reset={reset} />);
+
+    fireEvent.click(screen.getByRole("button", { name: "Try again" }));
+
+    expect(reset).toHaveBeenCalledTimes(1);
+    expect(refresh).toHaveBeenCalledTimes(1);
+  });
+
+  it("renders a dashboard escape hatch", () => {
+    render(<ErrorPage error={new Error("boom")} reset={vi.fn()} />);
+
+    expect(screen.getByRole("link", { name: "Back to dashboard" })).toHaveAttribute("href", "/");
+  });
+});
diff --git a/packages/web/src/app/error.tsx b/packages/web/src/app/error.tsx
new file mode 100644
index 000000000..ba96be99a
--- /dev/null
+++ b/packages/web/src/app/error.tsx
@@ -0,0 +1,38 @@
+"use client";
+
+import { useRouter } from "next/navigation";
+import { useEffect } from "react";
+import { ErrorDisplay } from "@/components/ErrorDisplay";
+
+export default function Error({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string };
+  reset: () => void;
+}) {
+  const router = useRouter();
+
+  useEffect(() => {
+    console.error(error);
+  }, [error]);
+
+  return (
+    <ErrorDisplay
+      title="Something went wrong"
+      message="The dashboard hit an unexpected error. Try reloading the route data or head back to the main dashboard."
+      tone="warning"
+      primaryAction={{
+        label: "Try again",
+        onClick: () => {
+          reset();
+          router.refresh();
+        },
+      }}
+      secondaryAction={{ label: "Back to dashboard", href: "/" }}
+      error={error}
+      compact
+      chrome="card"
+    />
+  );
+}
diff --git a/packages/web/src/app/global-error.test.tsx b/packages/web/src/app/global-error.test.tsx
new file mode 100644
index 000000000..461d1c744
--- /dev/null
+++ b/packages/web/src/app/global-error.test.tsx
@@ -0,0 +1,72 @@
+import { fireEvent, render, screen } from "@testing-library/react";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const errorDisplaySpy = vi.fn();
+
+vi.mock("@/components/ErrorDisplay", () => ({
+  ErrorDisplay: (props: {
+    title: string;
+    message: string;
+    primaryAction?: { label: string; onClick?: () => void };
+    secondaryAction?: { label: string; onClick?: () => void };
+  }) => {
+    errorDisplaySpy(props);
+    return (
+      <div>
+        <div>{props.title}</div>
+        <div>{props.message}</div>
+        {props.primaryAction ? (
+          <button type="button" onClick={props.primaryAction.onClick}>
+            {props.primaryAction.label}
+          </button>
+        ) : null}
+        {props.secondaryAction ? (
+          <button type="button" onClick={props.secondaryAction.onClick}>
+            {props.secondaryAction.label}
+          </button>
+        ) : null}
+      </div>
+    );
+  },
+}));
+
+import GlobalError from "./global-error";
+
+describe("Global error boundary", () => {
+  beforeEach(() => {
+    vi.spyOn(console, "error").mockImplementation(() => {});
+    errorDisplaySpy.mockClear();
+    Object.defineProperty(window, "location", {
+      configurable: true,
+      value: { reload: vi.fn() },
+    });
+  });
+
+  it("calls reset when retrying", () => {
+    const reset = vi.fn();
+
+    render(<GlobalError error={new Error("layout failed")} reset={reset} />);
+
+    fireEvent.click(screen.getByRole("button", { name: "Try again" }));
+    expect(reset).toHaveBeenCalledTimes(1);
+  });
+
+  it("reloads the page on demand", () => {
+    render(<GlobalError error={new Error("layout failed")} reset={vi.fn()} />);
+
+    fireEvent.click(screen.getByRole("button", { name: "Reload page" }));
+    expect(window.location.reload).toHaveBeenCalledTimes(1);
+  });
+
+  it("passes the expected shell copy to ErrorDisplay", () => {
+    render(<GlobalError error={new Error("layout failed")} reset={vi.fn()} />);
+
+    expect(errorDisplaySpy).toHaveBeenCalledWith(
+      expect.objectContaining({
+        title: "Something broke at the app shell",
+        message:
+          "The dashboard could not recover from this error at the layout level. Try again first, then reload the page if it still fails.",
+      }),
+    );
+  });
+});
diff --git a/packages/web/src/app/global-error.tsx b/packages/web/src/app/global-error.tsx
new file mode 100644
index 000000000..fa1784e5f
--- /dev/null
+++ b/packages/web/src/app/global-error.tsx
@@ -0,0 +1,31 @@
+"use client";
+
+import { useEffect } from "react";
+import { ErrorDisplay } from "@/components/ErrorDisplay";
+
+export default function GlobalError({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string };
+  reset: () => void;
+}) {
+  useEffect(() => {
+    console.error(error);
+  }, [error]);
+
+  return (
+    <html lang="en" className="dark">
+      <body className="bg-[var(--color-bg-base)] text-[var(--color-text-primary)] antialiased">
+        <ErrorDisplay
+          title="Something broke at the app shell"
+          message="The dashboard could not recover from this error at the layout level. Try again first, then reload the page if it still fails."
+          tone="error"
+          primaryAction={{ label: "Try again", onClick: reset }}
+          secondaryAction={{ label: "Reload page", onClick: () => window.location.reload() }}
+          error={error}
+        />
+      </body>
+    </html>
+  );
+}
diff --git a/packages/web/src/app/not-found.test.tsx b/packages/web/src/app/not-found.test.tsx
index c370cae0a..c2678acbc 100644
--- a/packages/web/src/app/not-found.test.tsx
+++ b/packages/web/src/app/not-found.test.tsx
@@ -18,9 +18,18 @@ describe("NotFound (global)", () => {
     expect(screen.getByText("Page not found")).toBeInTheDocument();
   });
 
+  it("renders descriptive copy", () => {
+    render(<NotFound />);
+    expect(
+      screen.getByText(
+        "This route does not exist in the dashboard. Return to the main view to pick an active project or session.",
+      ),
+    ).toBeInTheDocument();
+  });
+
   it("renders a link back to the dashboard", () => {
     render(<NotFound />);
-    const link = screen.getByText("← Back to dashboard");
+    const link = screen.getByText("Back to dashboard");
     expect(link).toBeInTheDocument();
     expect(link.closest("a")).toHaveAttribute("href", "/");
   });
diff --git a/packages/web/src/app/not-found.tsx b/packages/web/src/app/not-found.tsx
index 868beb5f0..8b817324d 100644
--- a/packages/web/src/app/not-found.tsx
+++ b/packages/web/src/app/not-found.tsx
@@ -1,27 +1,12 @@
-import Link from "next/link";
+import { ErrorDisplay } from "@/components/ErrorDisplay";
 
 export default function NotFound() {
   return (
-    <div className="flex min-h-screen flex-col items-center justify-center gap-4 bg-[var(--color-bg-base)]">
-      <svg
-        className="h-8 w-8 text-[var(--color-border-strong)]"
-        fill="none"
-        stroke="currentColor"
-        strokeWidth="1.5"
-        viewBox="0 0 24 24"
-      >
-        <rect x="2" y="4" width="20" height="16" rx="2" />
-        <path d="M6 9l4 3-4 3M13 15h5" />
-      </svg>
-      <p className="text-[13px] text-[var(--color-text-muted)]">
-        Page not found
-      </p>
-      <Link
-        href="/"
-        className="text-[12px] text-[var(--color-accent)] hover:underline"
-      >
-        ← Back to dashboard
-      </Link>
-    </div>
+    <ErrorDisplay
+      title="Page not found"
+      message="This route does not exist in the dashboard. Return to the main view to pick an active project or session."
+      tone="not-found"
+      primaryAction={{ label: "Back to dashboard", href: "/" }}
+    />
   );
 }
diff --git a/packages/web/src/app/sessions/[id]/error.test.tsx b/packages/web/src/app/sessions/[id]/error.test.tsx
new file mode 100644
index 000000000..adcfb9d68
--- /dev/null
+++ b/packages/web/src/app/sessions/[id]/error.test.tsx
@@ -0,0 +1,37 @@
+import { fireEvent, render, screen } from "@testing-library/react";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const refresh = vi.fn();
+
+vi.mock("next/navigation", () => ({
+  useRouter: () => ({ refresh }),
+}));
+
+import SessionError from "./error";
+
+describe("Session error boundary", () => {
+  beforeEach(() => {
+    vi.spyOn(console, "error").mockImplementation(() => {});
+  });
+
+  it("retries with reset and router refresh", () => {
+    const reset = vi.fn();
+
+    render(<SessionError error={new Error("HTTP 500")} reset={reset} />);
+
+    fireEvent.click(screen.getByRole("button", { name: "Try again" }));
+
+    expect(reset).toHaveBeenCalledTimes(1);
+    expect(refresh).toHaveBeenCalledTimes(1);
+  });
+
+  it("shows a session-specific message", () => {
+    render(<SessionError error={new Error("Network request failed")} reset={vi.fn()} />);
+
+    expect(
+      screen.getByText(
+        "The session request failed before the dashboard got a response. Check the server connection and try again.",
+      ),
+    ).toBeInTheDocument();
+  });
+});
diff --git a/packages/web/src/app/sessions/[id]/error.tsx b/packages/web/src/app/sessions/[id]/error.tsx
new file mode 100644
index 000000000..f9a0011c1
--- /dev/null
+++ b/packages/web/src/app/sessions/[id]/error.tsx
@@ -0,0 +1,55 @@
+"use client";
+
+import { useRouter } from "next/navigation";
+import { useEffect } from "react";
+import { ErrorDisplay } from "@/components/ErrorDisplay";
+
+function getSessionErrorMessage(error: Error): string {
+  const normalized = error.message.toLowerCase();
+  if (normalized.includes("network")) {
+    return "The session request failed before the dashboard got a response. Check the server connection and try again.";
+  }
+  if (normalized.includes("403")) {
+    return "The dashboard could not access this session. Permissions or auth may have changed.";
+  }
+  if (normalized.includes("404")) {
+    return "This session is no longer available. It may have been removed while the page was open.";
+  }
+  if (normalized.includes("500")) {
+    return "The server returned an internal error while loading this session. Try re-fetching the session data.";
+  }
+  return "The dashboard could not load this session cleanly. Try again to re-fetch the latest state.";
+}
+
+export default function SessionError({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string };
+  reset: () => void;
+}) {
+  const router = useRouter();
+
+  useEffect(() => {
+    console.error(error);
+  }, [error]);
+
+  return (
+    <ErrorDisplay
+      title="Failed to load session"
+      message={getSessionErrorMessage(error)}
+      tone="error"
+      primaryAction={{
+        label: "Try again",
+        onClick: () => {
+          reset();
+          router.refresh();
+        },
+      }}
+      secondaryAction={{ label: "Back to dashboard", href: "/" }}
+      error={error}
+      compact
+      chrome="card"
+    />
+  );
+}
diff --git a/packages/web/src/app/sessions/[id]/not-found.test.tsx b/packages/web/src/app/sessions/[id]/not-found.test.tsx
index 7edf1f315..614ec96de 100644
--- a/packages/web/src/app/sessions/[id]/not-found.test.tsx
+++ b/packages/web/src/app/sessions/[id]/not-found.test.tsx
@@ -22,14 +22,14 @@ describe("SessionNotFound", () => {
     render(<SessionNotFound />);
     expect(
       screen.getByText(
-        "The session you\u2019re looking for doesn\u2019t exist or has been deleted.",
+        "The session you’re looking for does not exist anymore, or the link is stale.",
       ),
     ).toBeInTheDocument();
   });
 
   it("renders a link back to the dashboard", () => {
     render(<SessionNotFound />);
-    const link = screen.getByText("← Back to dashboard");
+    const link = screen.getByText("Back to dashboard");
     expect(link).toBeInTheDocument();
     expect(link.closest("a")).toHaveAttribute("href", "/");
   });
diff --git a/packages/web/src/app/sessions/[id]/not-found.tsx b/packages/web/src/app/sessions/[id]/not-found.tsx
index 7fd7481fb..4fb654b60 100644
--- a/packages/web/src/app/sessions/[id]/not-found.tsx
+++ b/packages/web/src/app/sessions/[id]/not-found.tsx
@@ -1,31 +1,14 @@
-import Link from "next/link";
+import { ErrorDisplay } from "@/components/ErrorDisplay";
 
 export default function SessionNotFound() {
   return (
-    <div className="flex min-h-screen flex-col items-center justify-center gap-4 bg-[var(--color-bg-base)]">
-      <svg
-        className="h-8 w-8 text-[var(--color-border-strong)]"
-        fill="none"
-        stroke="currentColor"
-        strokeWidth="1.5"
-        viewBox="0 0 24 24"
-      >
-        <rect x="2" y="4" width="20" height="16" rx="2" />
-        <path d="M6 9l4 3-4 3M13 15h5" />
-      </svg>
-      <p className="text-[13px] text-[var(--color-text-muted)]">
-        Session not found
-      </p>
-      <p className="text-[12px] text-[var(--color-text-tertiary)]">
-        The session you&rsquo;re looking for doesn&rsquo;t exist or has been
-        deleted.
-      </p>
-      <Link
-        href="/"
-        className="text-[12px] text-[var(--color-accent)] hover:underline"
-      >
-        ← Back to dashboard
-      </Link>
-    </div>
+    <ErrorDisplay
+      title="Session not found"
+      message="The session you’re looking for does not exist anymore, or the link is stale."
+      tone="not-found"
+      primaryAction={{ label: "Back to dashboard", href: "/" }}
+      compact
+      chrome="card"
+    />
   );
 }
diff --git a/packages/web/src/app/sessions/[id]/page.test.tsx b/packages/web/src/app/sessions/[id]/page.test.tsx
index 45eb15790..3b2243e5a 100644
--- a/packages/web/src/app/sessions/[id]/page.test.tsx
+++ b/packages/web/src/app/sessions/[id]/page.test.tsx
@@ -1,11 +1,17 @@
-import { act, render } from "@testing-library/react";
+import React, { type ReactNode } from "react";
+import { act, render, screen } from "@testing-library/react";
 import { beforeEach, afterEach, describe, expect, it, vi } from "vitest";
 import type { DashboardSession } from "@/lib/types";
 
 const sessionDetailSpy = vi.fn();
+const notFoundError = new Error("NEXT_NOT_FOUND");
+const notFoundSpy = vi.fn(() => {
+  throw notFoundError;
+});
 
 vi.mock("next/navigation", () => ({
   useParams: () => ({ id: "worker-1" }),
+  notFound: notFoundSpy,
 }));
 
 vi.mock("@/components/SessionDetail", () => ({
@@ -40,10 +46,32 @@ async function flushAsyncWork(): Promise<void> {
   });
 }
 
+class TestErrorBoundary extends React.Component<
+  { children: ReactNode },
+  { error: Error | null }
+> {
+  constructor(props: { children: ReactNode }) {
+    super(props);
+    this.state = { error: null };
+  }
+
+  static getDerivedStateFromError(error: Error) {
+    return { error };
+  }
+
+  render() {
+    if (this.state.error) {
+      return <div data-testid="route-error">{this.state.error.message}</div>;
+    }
+    return this.props.children;
+  }
+}
+
 describe("SessionPage project polling", () => {
   beforeEach(() => {
     vi.useFakeTimers();
     sessionDetailSpy.mockClear();
+    vi.spyOn(console, "error").mockImplementation(() => {});
 
     const eventSourceMock = {
       addEventListener: vi.fn(),
@@ -59,6 +87,7 @@ describe("SessionPage project polling", () => {
   afterEach(() => {
     vi.useRealTimers();
     vi.restoreAllMocks();
+    notFoundSpy.mockReset();
   });
 
   it("resolves orchestrator nav once for non-orchestrator pages and skips repeated project polling", async () => {
@@ -125,4 +154,70 @@ describe("SessionPage project polling", () => {
       ),
     ).toHaveLength(1);
   });
+
+  it("routes 404 responses through notFound()", async () => {
+    global.fetch = vi.fn(async (input: RequestInfo | URL) => {
+      const url = String(input);
+      if (url === "/api/projects") {
+        return {
+          ok: true,
+          status: 200,
+          json: async () => ({ projects: [] }),
+        } as Response;
+      }
+
+      if (url === "/api/sessions/worker-1") {
+        return {
+          ok: false,
+          status: 404,
+          json: async () => ({}),
+        } as Response;
+      }
+
+      throw new Error(`Unexpected fetch: ${url}`);
+    }) as typeof fetch;
+
+    const { default: SessionPage } = await import("./page");
+
+    render(<SessionPage />);
+    await flushAsyncWork();
+
+    expect(notFoundSpy).toHaveBeenCalled();
+    expect(screen.queryByTestId("session-detail")).not.toBeInTheDocument();
+  });
+
+  it("throws non-404 session fetch failures to the route error boundary", async () => {
+    global.fetch = vi.fn(async (input: RequestInfo | URL) => {
+      const url = String(input);
+      if (url === "/api/projects") {
+        return {
+          ok: true,
+          status: 200,
+          json: async () => ({ projects: [] }),
+        } as Response;
+      }
+
+      if (url === "/api/sessions/worker-1") {
+        return {
+          ok: false,
+          status: 500,
+          json: async () => ({}),
+        } as Response;
+      }
+
+      throw new Error(`Unexpected fetch: ${url}`);
+    }) as typeof fetch;
+
+    const { default: SessionPage } = await import("./page");
+
+    render(
+      <TestErrorBoundary>
+        <SessionPage />
+      </TestErrorBoundary>,
+    );
+
+    await flushAsyncWork();
+
+    expect(screen.getByTestId("route-error")).toHaveTextContent("HTTP 500");
+  });
 });
diff --git a/packages/web/src/app/sessions/[id]/page.tsx b/packages/web/src/app/sessions/[id]/page.tsx
index cf0bf2fe3..f90bf9a81 100644
--- a/packages/web/src/app/sessions/[id]/page.tsx
+++ b/packages/web/src/app/sessions/[id]/page.tsx
@@ -1,7 +1,7 @@
 "use client";
 
 import { useEffect, useState, useCallback, useRef } from "react";
-import { useParams } from "next/navigation";
+import { notFound, useParams } from "next/navigation";
 import { isOrchestratorSession } from "@composio/ao-core/types";
 import { SessionDetail } from "@/components/SessionDetail";
 import { type DashboardSession, type ActivityState, getAttentionLevel, type AttentionLevel } from "@/lib/types";
@@ -63,7 +63,8 @@ export default function SessionPage() {
   const [zoneCounts, setZoneCounts] = useState<ZoneCounts | null>(null);
   const [projectOrchestratorId, setProjectOrchestratorId] = useState<string | null | undefined>(undefined);
   const [loading, setLoading] = useState(true);
-  const [error, setError] = useState<string | null>(null);
+  const [routeError, setRouteError] = useState<Error | null>(null);
+  const [sessionMissing, setSessionMissing] = useState(false);
   const [prefixByProject, setPrefixByProject] = useState<Map<string, string>>(new Map());
   const sessionProjectId = session?.projectId ?? null;
   const allPrefixes = [...prefixByProject.values()];
@@ -119,17 +120,18 @@ export default function SessionPage() {
     try {
       const res = await fetch(`/api/sessions/${encodeURIComponent(id)}`);
       if (res.status === 404) {
-        setError("Session not found");
+        setSessionMissing(true);
         setLoading(false);
         return;
       }
       if (!res.ok) throw new Error(`HTTP ${res.status}`);
       const data = (await res.json()) as DashboardSession;
       setSession(data);
-      setError(null);
+      setRouteError(null);
+      setSessionMissing(false);
     } catch (err) {
       console.error("Failed to fetch session:", err);
-      setError("Failed to load session");
+      setRouteError(err instanceof Error ? err : new Error("Failed to load session"));
     } finally {
       setLoading(false);
     }
@@ -211,17 +213,17 @@ export default function SessionPage() {
     );
   }
 
-  if (error || !session) {
-    return (
-      <div className="flex min-h-screen flex-col items-center justify-center gap-4 bg-[var(--color-bg-base)]">
-        <div className="text-[13px] text-[var(--color-status-error)]">
-          {error ?? "Session not found"}
-        </div>
-        <a href="/" className="text-[12px] text-[var(--color-accent)] hover:underline">
-          ← Back to dashboard
-        </a>
-      </div>
-    );
+  if (sessionMissing) {
+    notFound();
+    return null;
+  }
+
+  if (routeError) {
+    throw routeError;
+  }
+
+  if (!session) {
+    throw new Error("Session data was unavailable after loading completed");
   }
 
   return (
diff --git a/packages/web/src/components/ErrorDisplay.tsx b/packages/web/src/components/ErrorDisplay.tsx
new file mode 100644
index 000000000..e520ab979
--- /dev/null
+++ b/packages/web/src/components/ErrorDisplay.tsx
@@ -0,0 +1,204 @@
+"use client";
+
+import Link from "next/link";
+import { type ReactNode } from "react";
+
+type ErrorTone = "error" | "warning" | "not-found";
+
+interface ErrorAction {
+  label: string;
+  onClick?: () => void;
+  href?: string;
+}
+
+interface ErrorDisplayProps {
+  title: string;
+  message: string;
+  tone?: ErrorTone;
+  detailsTitle?: string;
+  error?: Error & { digest?: string };
+  primaryAction?: ErrorAction;
+  secondaryAction?: ErrorAction;
+  compact?: boolean;
+  chrome?: "page" | "card";
+  children?: ReactNode;
+}
+
+const toneMeta: Record<ErrorTone, { accent: string; bg: string; border: string; label: string }> = {
+  error: {
+    accent: "var(--color-status-error)",
+    bg: "var(--color-tint-red)",
+    border: "color-mix(in srgb, var(--color-status-error) 24%, transparent)",
+    label: "error",
+  },
+  warning: {
+    accent: "var(--color-status-attention)",
+    bg: "var(--color-tint-yellow)",
+    border: "color-mix(in srgb, var(--color-status-attention) 24%, transparent)",
+    label: "warning",
+  },
+  "not-found": {
+    accent: "var(--color-accent)",
+    bg: "var(--color-tint-blue)",
+    border: "color-mix(in srgb, var(--color-accent) 24%, transparent)",
+    label: "missing",
+  },
+};
+
+function TerminalIcon({ accent }: { accent: string }) {
+  return (
+    <div
+      className="flex h-14 w-14 items-center justify-center rounded-2xl border"
+      style={{
+        background: `linear-gradient(180deg, color-mix(in srgb, ${accent} 16%, var(--color-bg-elevated)) 0%, var(--color-bg-surface) 100%)`,
+        borderColor: `color-mix(in srgb, ${accent} 18%, var(--color-border-default))`,
+        boxShadow: "var(--detail-card-shadow)",
+      }}
+    >
+      <svg
+        className="h-7 w-7"
+        fill="none"
+        stroke="currentColor"
+        strokeWidth="1.6"
+        style={{ color: accent }}
+        viewBox="0 0 24 24"
+      >
+        <rect x="2.5" y="4.5" width="19" height="15" rx="3" />
+        <path d="M6.5 9.5l3.25 2.5-3.25 2.5M12.75 15h4.75" />
+      </svg>
+    </div>
+  );
+}
+
+function ActionButton({ action, primary = false }: { action: ErrorAction; primary?: boolean }) {
+  const className = primary
+    ? "inline-flex items-center justify-center rounded-full border px-4 py-2 text-[12px] font-semibold transition-colors hover:no-underline"
+    : "inline-flex items-center justify-center rounded-full border px-4 py-2 text-[12px] font-medium transition-colors hover:no-underline";
+  const style = primary
+    ? {
+        background: "var(--color-accent)",
+        color: "var(--color-text-inverse)",
+        borderColor: "color-mix(in srgb, var(--color-accent) 72%, transparent)",
+      }
+    : {
+        background: "var(--color-bg-surface)",
+        color: "var(--color-text-secondary)",
+        borderColor: "var(--color-border-default)",
+      };
+
+  if (action.href) {
+    return (
+      <Link href={action.href} className={className} style={style}>
+        {action.label}
+      </Link>
+    );
+  }
+
+  return (
+    <button type="button" onClick={action.onClick} className={className} style={style}>
+      {action.label}
+    </button>
+  );
+}
+
+export function ErrorDisplay({
+  title,
+  message,
+  tone = "error",
+  detailsTitle = "Technical details",
+  error,
+  primaryAction,
+  secondaryAction,
+  compact = false,
+  chrome = "page",
+  children,
+}: ErrorDisplayProps) {
+  const meta = toneMeta[tone];
+  const hasDetails = Boolean(error?.digest || error?.message || error?.stack);
+
+  return (
+    <div
+      className={`flex w-full items-center justify-center px-6 py-10 ${compact ? "min-h-[calc(100vh-4rem)]" : "min-h-screen"}`}
+      style={{
+        background:
+          chrome === "page"
+            ? "radial-gradient(circle at top, var(--color-body-gradient-blue), transparent 35%), var(--color-bg-base)"
+            : "transparent",
+      }}
+    >
+      <div
+        className="w-full max-w-[36rem] rounded-[28px] border p-6 sm:p-8"
+        style={{
+          background:
+            "linear-gradient(180deg, color-mix(in srgb, var(--color-bg-elevated) 88%, transparent) 0%, var(--color-bg-surface) 100%)",
+          borderColor: "var(--color-border-default)",
+          boxShadow: "var(--detail-card-shadow)",
+        }}
+      >
+        <div className="flex flex-col gap-6">
+          <div className="flex flex-col gap-4 sm:flex-row sm:items-start">
+            <TerminalIcon accent={meta.accent} />
+            <div className="min-w-0 flex-1">
+              <div
+                className="mb-3 inline-flex items-center rounded-full border px-2.5 py-1 font-[var(--font-mono)] text-[10px] font-medium uppercase tracking-[0.22em]"
+                style={{
+                  color: meta.accent,
+                  background: meta.bg,
+                  borderColor: meta.border,
+                }}
+              >
+                {meta.label}
+              </div>
+              <h1 className="text-[24px] font-semibold tracking-[-0.04em] text-[var(--color-text-primary)]">
+                {title}
+              </h1>
+              <p className="mt-2 max-w-[34rem] text-[14px] leading-6 text-[var(--color-text-secondary)]">
+                {message}
+              </p>
+            </div>
+          </div>
+
+          {(primaryAction || secondaryAction) && (
+            <div className="flex flex-wrap gap-3">
+              {primaryAction ? <ActionButton action={primaryAction} primary /> : null}
+              {secondaryAction ? <ActionButton action={secondaryAction} /> : null}
+            </div>
+          )}
+
+          {children}
+
+          {hasDetails ? (
+            <details
+              className="rounded-2xl border"
+              style={{
+                background: "color-mix(in srgb, var(--color-bg-elevated) 84%, transparent)",
+                borderColor: "var(--color-border-subtle)",
+              }}
+            >
+              <summary className="cursor-pointer list-none px-4 py-3 text-[12px] font-medium text-[var(--color-text-secondary)]">
+                {detailsTitle}
+              </summary>
+              <div className="border-t px-4 py-4" style={{ borderColor: "var(--color-border-subtle)" }}>
+                {error?.digest ? (
+                  <p className="mb-3 font-[var(--font-mono)] text-[11px] text-[var(--color-text-tertiary)]">
+                    digest: {error.digest}
+                  </p>
+                ) : null}
+                {error?.message ? (
+                  <p className="mb-3 text-[12px] leading-5 text-[var(--color-text-secondary)]">
+                    {error.message}
+                  </p>
+                ) : null}
+                {error?.stack ? (
+                  <pre className="overflow-x-auto whitespace-pre-wrap font-[var(--font-mono)] text-[11px] leading-5 text-[var(--color-text-tertiary)]">
+                    {error.stack}
+                  </pre>
+                ) : null}
+              </div>
+            </details>
+          ) : null}
+        </div>
+      </div>
+    </div>
+  );
+}
diff --git a/packages/web/src/components/__tests__/ErrorDisplay.test.tsx b/packages/web/src/components/__tests__/ErrorDisplay.test.tsx
new file mode 100644
index 000000000..1c86bff0e
--- /dev/null
+++ b/packages/web/src/components/__tests__/ErrorDisplay.test.tsx
@@ -0,0 +1,50 @@
+import { fireEvent, render, screen } from "@testing-library/react";
+import { describe, expect, it, vi } from "vitest";
+
+vi.mock("next/link", () => ({
+  default: ({
+    children,
+    ...props
+  }: React.PropsWithChildren<React.AnchorHTMLAttributes<HTMLAnchorElement>>) => (
+    <a {...props}>{children}</a>
+  ),
+}));
+
+import { ErrorDisplay } from "../ErrorDisplay";
+
+describe("ErrorDisplay", () => {
+  it("renders title, message, and actions", () => {
+    const onRetry = vi.fn();
+
+    render(
+      <ErrorDisplay
+        title="Failed to load session"
+        message="Try again."
+        primaryAction={{ label: "Try again", onClick: onRetry }}
+        secondaryAction={{ label: "Back to dashboard", href: "/" }}
+      />,
+    );
+
+    expect(screen.getByText("Failed to load session")).toBeInTheDocument();
+    expect(screen.getByText("Try again.")).toBeInTheDocument();
+
+    fireEvent.click(screen.getByRole("button", { name: "Try again" }));
+    expect(onRetry).toHaveBeenCalledTimes(1);
+
+    expect(screen.getByRole("link", { name: "Back to dashboard" })).toHaveAttribute("href", "/");
+  });
+
+  it("renders technical details when provided", () => {
+    render(
+      <ErrorDisplay
+        title="Something went wrong"
+        message="Details are available."
+        error={Object.assign(new Error("HTTP 500"), { digest: "abc123" })}
+      />,
+    );
+
+    expect(screen.getByText("Technical details")).toBeInTheDocument();
+    expect(screen.getByText(/digest: abc123/)).toBeInTheDocument();
+    expect(screen.getByText("HTTP 500")).toBeInTheDocument();
+  });
+});