diff --git a/canvas/src/app/page.tsx b/canvas/src/app/page.tsx
index e785cb9a..b8976a35 100644
--- a/canvas/src/app/page.tsx
+++ b/canvas/src/app/page.tsx
@@ -10,6 +10,9 @@ import { api } from "@/lib/api";
 import type { WorkspaceData } from "@/store/socket";
 
 export default function Home() {
+  const hydrationError = useCanvasStore((s) => s.hydrationError);
+  const setHydrationError = useCanvasStore((s) => s.setHydrationError);
+
   useEffect(() => {
     connectSocket();
 
@@ -23,8 +26,11 @@ export default function Home() {
         useCanvasStore.getState().setViewport(viewport);
       }
     }).catch((err) => {
-      // Initial hydration failed — socket reconnect will retry
+      // Initial hydration failed — show error banner to user
       console.error("Canvas: initial hydration failed", err);
+      useCanvasStore.getState().setHydrationError(
+        err instanceof Error && err.message ? err.message : "Failed to load canvas"
+      );
     });
 
     return () => {
@@ -37,6 +43,23 @@ export default function Home() {
       <Canvas />
       <Legend />
       <CommunicationOverlay />
+      {hydrationError && (
+        <div
+          role="alert"
+          className="fixed inset-0 flex flex-col items-center justify-center bg-zinc-950 text-zinc-300 gap-4 z-[9999]"
+        >
+          <p className="text-zinc-400 text-sm">{hydrationError}</p>
+          <button
+            onClick={() => {
+              setHydrationError(null);
+              window.location.reload();
+            }}
+            className="px-4 py-2 bg-blue-600 hover:bg-blue-500 text-white rounded-md text-sm"
+          >
+            Retry
+          </button>
+        </div>
+      )}
     </>
   );
 }
diff --git a/canvas/src/components/ContextMenu.tsx b/canvas/src/components/ContextMenu.tsx
index 5e1d2f4f..c03fb8fa 100644
--- a/canvas/src/components/ContextMenu.tsx
+++ b/canvas/src/components/ContextMenu.tsx
@@ -235,6 +235,14 @@ export function ContextMenu() {
     closeContextMenu();
   }, [contextMenu, nestNode, closeContextMenu]);
 
+  const handleZoomToTeam = useCallback(() => {
+    if (!contextMenu) return;
+    window.dispatchEvent(
+      new CustomEvent("molecule:zoom-to-team", { detail: { nodeId: contextMenu.nodeId } })
+    );
+    closeContextMenu();
+  }, [contextMenu, closeContextMenu]);
+
   if (!contextMenu) return null;
 
   const isOfflineOrFailed = contextMenu.nodeData.status === "offline" || contextMenu.nodeData.status === "failed";
@@ -253,7 +261,10 @@ export function ContextMenu() {
       ? [{ label: "Extract from Team", icon: "⤴", action: handleRemoveFromTeam }]
       : []),
     ...(hasChildren
-      ? [{ label: "Collapse Team", icon: "◁", action: handleCollapse }]
+      ? [
+          { label: "Collapse Team", icon: "◁", action: handleCollapse },
+          { label: "Zoom to Team", icon: "⊕", action: handleZoomToTeam },
+        ]
       : [{ label: "Expand to Team", icon: "▷", action: handleExpand }]),
     { label: "", icon: "", action: () => {}, divider: true },
     ...(isPaused
diff --git a/canvas/src/components/CreateWorkspaceDialog.tsx b/canvas/src/components/CreateWorkspaceDialog.tsx
index 4b0a8065..9c5f4dd0 100644
--- a/canvas/src/components/CreateWorkspaceDialog.tsx
+++ b/canvas/src/components/CreateWorkspaceDialog.tsx
@@ -1,6 +1,6 @@
 "use client";
 
-import { useState, useEffect } from "react";
+import { useState, useEffect, useRef, useCallback } from "react";
 import * as Dialog from "@radix-ui/react-dialog";
 import { api } from "@/lib/api";
 
@@ -50,6 +50,33 @@ export function CreateWorkspaceButton() {
   const [hermesProvider, setHermesProvider] = useState("anthropic");
   const [hermesApiKey, setHermesApiKey] = useState("");
 
+  // Refs for roving tabIndex on the tier radio group (WCAG 2.1 arrow-key nav)
+  const radioRefs = useRef<Array<HTMLButtonElement | null>>([]);
+  const TIERS = [
+    { value: 1, label: "T1", desc: "Sandboxed" },
+    { value: 2, label: "T2", desc: "Standard" },
+    { value: 3, label: "T3", desc: "Full Access" },
+  ];
+
+  const handleRadioKeyDown = useCallback(
+    (e: React.KeyboardEvent, currentIndex: number) => {
+      if (e.key === "ArrowDown" || e.key === "ArrowRight") {
+        e.preventDefault();
+        const next = (currentIndex + 1) % TIERS.length;
+        setTier(TIERS[next].value);
+        radioRefs.current[next]?.focus();
+      } else if (e.key === "ArrowUp" || e.key === "ArrowLeft") {
+        e.preventDefault();
+        const prev = (currentIndex - 1 + TIERS.length) % TIERS.length;
+        setTier(TIERS[prev].value);
+        radioRefs.current[prev]?.focus();
+      }
+    },
+    // TIERS is stable (module-level constant pattern), setTier is stable from useState
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    []
+  );
+
   const isHermes = template.trim().toLowerCase() === "hermes";
 
   // Reset form and load workspaces whenever dialog opens
@@ -172,16 +199,15 @@ export function CreateWorkspaceButton() {
                 <div className="col-span-3 text-[11px] text-zinc-400 mb-1">
                   Tier
                 </div>
-                {[
-                  { value: 1, label: "T1", desc: "Sandboxed" },
-                  { value: 2, label: "T2", desc: "Standard" },
-                  { value: 3, label: "T3", desc: "Full Access" },
-                ].map((t) => (
+                {TIERS.map((t, idx) => (
                   <button
                     key={t.value}
+                    ref={(el) => { radioRefs.current[idx] = el; }}
                     role="radio"
                     aria-checked={tier === t.value}
+                    tabIndex={tier === t.value ? 0 : -1}
                     onClick={() => setTier(t.value)}
+                    onKeyDown={(e) => handleRadioKeyDown(e, idx)}
                     className={`py-2 rounded-lg text-center transition-colors ${
                       tier === t.value
                         ? "bg-blue-600/20 border border-blue-500/50 text-blue-300"
diff --git a/canvas/src/components/__tests__/ContextMenu.keyboard.test.tsx b/canvas/src/components/__tests__/ContextMenu.keyboard.test.tsx
index e8a1376f..8e878de2 100644
--- a/canvas/src/components/__tests__/ContextMenu.keyboard.test.tsx
+++ b/canvas/src/components/__tests__/ContextMenu.keyboard.test.tsx
@@ -163,4 +163,50 @@ describe("ContextMenu — keyboard accessibility", () => {
     const { container } = render(<ContextMenu />);
     expect(container.firstChild).toBeNull();
   });
+
+  // ── Zoom to Team (#557) ───────────────────────────────────────────────────
+
+  it("does NOT show 'Zoom to Team' when node has no children", () => {
+    mockStore.nodes = []; // no children
+    render(<ContextMenu />);
+    const items = screen.getAllByRole("menuitem");
+    const labels = items.map((el) => el.textContent ?? "");
+    expect(labels.some((l) => l.includes("Zoom to Team"))).toBe(false);
+  });
+
+  it("shows 'Zoom to Team' when the node has children", () => {
+    mockStore.nodes = [{ id: "child-1", data: { parentId: "ws-1" } }];
+    render(<ContextMenu />);
+    const items = screen.getAllByRole("menuitem");
+    const labels = items.map((el) => el.textContent ?? "");
+    expect(labels.some((l) => l.includes("Zoom to Team"))).toBe(true);
+  });
+
+  it("clicking 'Zoom to Team' dispatches molecule:zoom-to-team event", () => {
+    mockStore.nodes = [{ id: "child-1", data: { parentId: "ws-1" } }];
+    const dispatched: CustomEvent[] = [];
+    window.addEventListener("molecule:zoom-to-team", (e) => {
+      dispatched.push(e as CustomEvent);
+    });
+
+    render(<ContextMenu />);
+    const items = screen.getAllByRole("menuitem");
+    const zoomItem = items.find((el) => el.textContent?.includes("Zoom to Team"))!;
+    expect(zoomItem).toBeTruthy();
+    fireEvent.click(zoomItem);
+
+    expect(dispatched).toHaveLength(1);
+    expect(dispatched[0].detail.nodeId).toBe("ws-1");
+
+    window.removeEventListener("molecule:zoom-to-team", () => {});
+  });
+
+  it("clicking 'Zoom to Team' closes the context menu", () => {
+    mockStore.nodes = [{ id: "child-1", data: { parentId: "ws-1" } }];
+    render(<ContextMenu />);
+    const items = screen.getAllByRole("menuitem");
+    const zoomItem = items.find((el) => el.textContent?.includes("Zoom to Team"))!;
+    fireEvent.click(zoomItem);
+    expect(closeContextMenu).toHaveBeenCalled();
+  });
 });
diff --git a/canvas/src/components/__tests__/CreateWorkspaceDialog.a11y.test.tsx b/canvas/src/components/__tests__/CreateWorkspaceDialog.a11y.test.tsx
index f0bca774..8be0f0ac 100644
--- a/canvas/src/components/__tests__/CreateWorkspaceDialog.a11y.test.tsx
+++ b/canvas/src/components/__tests__/CreateWorkspaceDialog.a11y.test.tsx
@@ -89,4 +89,75 @@ describe("CreateWorkspaceDialog — accessibility", () => {
       expect(t2?.getAttribute("aria-checked")).toBe("true")
     );
   });
+
+  // ── Arrow-key navigation (WCAG 2.1 radio group) — Issue #556 ──────────────
+
+  it("selected radio has tabIndex=0, others have tabIndex=-1 (roving tabIndex)", async () => {
+    await openDialog();
+    const radios = screen.getAllByRole("radio");
+    const t1 = radios.find((r) => r.textContent?.includes("T1"))!;
+    const t2 = radios.find((r) => r.textContent?.includes("T2"))!;
+    const t3 = radios.find((r) => r.textContent?.includes("T3"))!;
+    // T1 is default selected
+    expect(t1.getAttribute("tabindex")).toBe("0");
+    expect(t2.getAttribute("tabindex")).toBe("-1");
+    expect(t3.getAttribute("tabindex")).toBe("-1");
+  });
+
+  it("ArrowDown moves selection from T1 to T2", async () => {
+    await openDialog();
+    const radios = screen.getAllByRole("radio");
+    const t1 = radios.find((r) => r.textContent?.includes("T1"))!;
+    const t2 = radios.find((r) => r.textContent?.includes("T2"))!;
+    t1.focus();
+    fireEvent.keyDown(t1, { key: "ArrowDown" });
+    await waitFor(() => expect(t2.getAttribute("aria-checked")).toBe("true"));
+    expect(t1.getAttribute("aria-checked")).toBe("false");
+  });
+
+  it("ArrowRight moves selection from T2 to T3", async () => {
+    await openDialog();
+    const radios = screen.getAllByRole("radio");
+    const t2 = radios.find((r) => r.textContent?.includes("T2"))!;
+    const t3 = radios.find((r) => r.textContent?.includes("T3"))!;
+    fireEvent.click(t2); // select T2 first
+    await waitFor(() => expect(t2.getAttribute("aria-checked")).toBe("true"));
+    t2.focus();
+    fireEvent.keyDown(t2, { key: "ArrowRight" });
+    await waitFor(() => expect(t3.getAttribute("aria-checked")).toBe("true"));
+  });
+
+  it("ArrowDown wraps from T3 back to T1", async () => {
+    await openDialog();
+    const radios = screen.getAllByRole("radio");
+    const t1 = radios.find((r) => r.textContent?.includes("T1"))!;
+    const t3 = radios.find((r) => r.textContent?.includes("T3"))!;
+    fireEvent.click(t3); // select T3 first
+    await waitFor(() => expect(t3.getAttribute("aria-checked")).toBe("true"));
+    t3.focus();
+    fireEvent.keyDown(t3, { key: "ArrowDown" });
+    await waitFor(() => expect(t1.getAttribute("aria-checked")).toBe("true"));
+  });
+
+  it("ArrowUp moves selection from T2 to T1", async () => {
+    await openDialog();
+    const radios = screen.getAllByRole("radio");
+    const t1 = radios.find((r) => r.textContent?.includes("T1"))!;
+    const t2 = radios.find((r) => r.textContent?.includes("T2"))!;
+    fireEvent.click(t2);
+    await waitFor(() => expect(t2.getAttribute("aria-checked")).toBe("true"));
+    t2.focus();
+    fireEvent.keyDown(t2, { key: "ArrowUp" });
+    await waitFor(() => expect(t1.getAttribute("aria-checked")).toBe("true"));
+  });
+
+  it("ArrowLeft wraps from T1 back to T3", async () => {
+    await openDialog();
+    const radios = screen.getAllByRole("radio");
+    const t1 = radios.find((r) => r.textContent?.includes("T1"))!;
+    const t3 = radios.find((r) => r.textContent?.includes("T3"))!;
+    t1.focus();
+    fireEvent.keyDown(t1, { key: "ArrowLeft" });
+    await waitFor(() => expect(t3.getAttribute("aria-checked")).toBe("true"));
+  });
 });
diff --git a/canvas/src/components/ui/RevealToggle.tsx b/canvas/src/components/ui/RevealToggle.tsx
index c0e051b1..82eaf929 100644
--- a/canvas/src/components/ui/RevealToggle.tsx
+++ b/canvas/src/components/ui/RevealToggle.tsx
@@ -1,3 +1,5 @@
+"use client";
+
 interface RevealToggleProps {
   revealed: boolean;
   onToggle: () => void;
diff --git a/canvas/src/store/__tests__/canvas.test.ts b/canvas/src/store/__tests__/canvas.test.ts
index 7316026c..6a5c2ce6 100644
--- a/canvas/src/store/__tests__/canvas.test.ts
+++ b/canvas/src/store/__tests__/canvas.test.ts
@@ -719,6 +719,33 @@ describe("misc state setters", () => {
   });
 });
 
+// ---------- hydrationError (#554) ----------
+
+describe("hydrationError", () => {
+  it("initial value is null", () => {
+    expect(useCanvasStore.getState().hydrationError).toBeNull();
+  });
+
+  it("setHydrationError stores an error message", () => {
+    useCanvasStore.getState().setHydrationError("Network timeout");
+    expect(useCanvasStore.getState().hydrationError).toBe("Network timeout");
+  });
+
+  it("setHydrationError(null) clears the error", () => {
+    useCanvasStore.getState().setHydrationError("Some error");
+    useCanvasStore.getState().setHydrationError(null);
+    expect(useCanvasStore.getState().hydrationError).toBeNull();
+  });
+
+  it("setHydrationError does not affect other state", () => {
+    useCanvasStore.getState().hydrate([makeWS({ id: "ws-x", name: "X" })]);
+    useCanvasStore.getState().setHydrationError("oops");
+    // Nodes should still be intact
+    expect(useCanvasStore.getState().nodes).toHaveLength(1);
+    expect(useCanvasStore.getState().nodes[0].id).toBe("ws-x");
+  });
+});
+
 // ---------- ACTIVITY_LOGGED event ----------
 
 describe("ACTIVITY_LOGGED event", () => {
diff --git a/canvas/src/store/canvas.ts b/canvas/src/store/canvas.ts
index 6056fafa..387c71e6 100644
--- a/canvas/src/store/canvas.ts
+++ b/canvas/src/store/canvas.ts
@@ -73,6 +73,9 @@ interface CanvasState {
   /** WebSocket connection status — drives the live indicator in the Toolbar. */
   wsStatus: "connected" | "connecting" | "disconnected";
   setWsStatus: (status: "connected" | "connecting" | "disconnected") => void;
+  /** Hydration error message — set when initial canvas load fails. Null when no error. */
+  hydrationError: string | null;
+  setHydrationError: (error: string | null) => void;
 }
 
 export const useCanvasStore = create<CanvasState>((set, get) => ({
@@ -84,6 +87,8 @@ export const useCanvasStore = create<CanvasState>((set, get) => ({
   contextMenu: null,
   wsStatus: "connecting",
   setWsStatus: (status) => set({ wsStatus: status }),
+  hydrationError: null,
+  setHydrationError: (error) => set({ hydrationError: error }),
 
   viewport: { x: 0, y: 0, zoom: 1 },