diff --git a/desktop/src/features/onboarding/ui/DefaultConfigStep.tsx b/desktop/src/features/onboarding/ui/DefaultConfigStep.tsx
index 1fd2e4bcab..2c20e18776 100644
--- a/desktop/src/features/onboarding/ui/DefaultConfigStep.tsx
+++ b/desktop/src/features/onboarding/ui/DefaultConfigStep.tsx
@@ -77,6 +77,11 @@ function AgentDefaultsSection({
     initialDraftRef.current?.isCustomModelEditing ?? false,
   );
   const [bakedEnv, setBakedEnv] = React.useState<BakedEnvEntry[]>([]);
+  const [configLoadError, setConfigLoadError] = React.useState(false);
+  const [configLoadNonce, retryConfigLoad] = React.useReducer(
+    (nonce: number) => nonce + 1,
+    0,
+  );
   const configRef = React.useRef<GlobalAgentConfig>(
     initialDraftRef.current?.config ?? EMPTY_GLOBAL_CONFIG,
   );
@@ -86,7 +91,9 @@ function AgentDefaultsSection({
   React.useEffect(() => {
     let unmounted = false;
 
-    async function loadDefaults() {
+    async function loadDefaults(_retryAttempt: number) {
+      setIsLoading(true);
+      setConfigLoadError(false);
       const [configResult, bakedEnvResult] = await Promise.allSettled([
         getGlobalAgentConfig(),
         getBakedBuildEnv(),
@@ -94,25 +101,27 @@ function AgentDefaultsSection({
 
       if (unmounted) return;
 
-      if (
-        initialDraftRef.current === null &&
-        configResult.status === "fulfilled"
-      ) {
-        configRef.current = configResult.value;
-        setConfig(configResult.value);
-      }
       if (bakedEnvResult.status === "fulfilled") {
         setBakedEnv(bakedEnvResult.value);
       }
+      if (configResult.status === "rejected") {
+        setConfigLoadError(true);
+        setIsLoading(false);
+        return;
+      }
+      if (initialDraftRef.current === null) {
+        configRef.current = configResult.value;
+        setConfig(configResult.value);
+      }
       setIsLoading(false);
     }
 
-    void loadDefaults();
+    void loadDefaults(configLoadNonce);
 
     return () => {
       unmounted = true;
     };
-  }, []);
+  }, [configLoadNonce]);
 
   const effectiveReadyRuntimeIds = React.useMemo(
     () =>
@@ -147,6 +156,7 @@ function AgentDefaultsSection({
   const configSurfaceLoading = isLoading || runtimesQuery.isLoading;
 
   const configSurfaceError =
+    configLoadError ||
     runtimesQuery.isError ||
     (!configSurfaceLoading &&
       effectiveReadyRuntimeIds.length > 0 &&
@@ -212,12 +222,14 @@ function AgentDefaultsSection({
       // configIsValid comes from AgentConfigFields' onValidityChange and
       // covers model + provider credentials — a harness selection alone is
       // not a working default (e.g. buzz-agent with no provider configured).
-      canComplete: selectedRuntimeId.length > 0 && configIsValid,
+      canComplete:
+        !configLoadError && selectedRuntimeId.length > 0 && configIsValid,
       commit: commitPersistence,
     });
   }, [
     commitPersistence,
     configIsValid,
+    configLoadError,
     onPersistenceStateChange,
     selectedRuntimeId,
   ]);
@@ -233,6 +245,20 @@ function AgentDefaultsSection({
           <Spinner className="h-4 w-4 border-2" />
           Loading…
         </div>
+      ) : configLoadError ? (
+        <div className="flex flex-col items-center gap-3 py-4 text-center text-sm">
+          <p className="text-destructive">
+            Couldn't load your existing default harness. Try again.
+          </p>
+          <Button
+            className={`${ONBOARDING_PRIMARY_CTA_CLASS} text-sm`}
+            disabled={isLoading}
+            onClick={retryConfigLoad}
+            type="button"
+          >
+            {isLoading ? "Checking…" : "Try again"}
+          </Button>
+        </div>
       ) : configSurfaceError ? (
         <p className="py-4 text-center text-sm text-destructive">
           Couldn't load harness settings. Go back and try again.
diff --git a/desktop/src/features/onboarding/ui/types.ts b/desktop/src/features/onboarding/ui/types.ts
index 2658850c75..5216bfefa4 100644
--- a/desktop/src/features/onboarding/ui/types.ts
+++ b/desktop/src/features/onboarding/ui/types.ts
@@ -62,8 +62,7 @@ export type ProfileStepActions = {
 
 export type SetupStepActions = {
   back: () => void;
-  next: (runtimeId: string) => void;
-  skip: () => void;
+  next: (readyRuntimeIds: readonly string[]) => void;
   navigateToAgentSettings?: () => void;
 };
 
diff --git a/desktop/src/testing/e2eBridge.ts b/desktop/src/testing/e2eBridge.ts
index af17af4f75..85f46f25d5 100644
--- a/desktop/src/testing/e2eBridge.ts
+++ b/desktop/src/testing/e2eBridge.ts
@@ -537,6 +537,8 @@ type E2eConfig = {
       model: string | null;
       preferred_runtime?: string | null;
     };
+    /** Sequenced `get_global_agent_config` failures. Null succeeds; a string throws. */
+    globalAgentConfigErrors?: (string | null)[];
     /** Explicit owner-only agent-access capability; independent of baked defaults. */
     ownerOnlyAccessBuild?: boolean;
     /** File-layer config returned by runtime id. */
@@ -13153,6 +13155,8 @@ export function maybeInstallE2eTauriMocks() {
         return config.mock?.runtimeFileConfigs?.[runtimeId] ?? null;
       }
       case "get_global_agent_config": {
+        const readError = activeConfig?.mock?.globalAgentConfigErrors?.shift();
+        if (readError) throw new Error(readError);
         // Return the mutable persisted mock value, seeded from the test config.
         return (
           mockGlobalAgentConfig ?? {
diff --git a/desktop/tests/e2e/onboarding-agent-defaults.spec.ts b/desktop/tests/e2e/onboarding-agent-defaults.spec.ts
index 3a15d21767..293e7e7362 100644
--- a/desktop/tests/e2e/onboarding-agent-defaults.spec.ts
+++ b/desktop/tests/e2e/onboarding-agent-defaults.spec.ts
@@ -491,6 +491,102 @@ test("defaults renders only fields supported by the selected harness", async ({
   ).toHaveCount(0);
 });
 
+test("failed config read blocks Next, preserves existing config, and retry succeeds", async ({
+  page,
+}) => {
+  await installMockBridge(
+    page,
+    {
+      acpRuntimesCatalog: [
+        runtime("claude", "available", { status: "logged_in" }),
+        runtime("codex", "available", { status: "logged_in" }),
+      ],
+      globalAgentConfig: {
+        env_vars: {
+          ANTHROPIC_API_KEY: "sk-existing",
+          BUZZ_AGENT_THINKING_EFFORT: "high",
+        },
+        provider: "anthropic",
+        model: "claude-sonnet-4",
+        preferred_runtime: "claude",
+      },
+      globalAgentConfigErrors: ["temporary config read failure", null],
+    },
+    { skipCommunitySeed: true, skipOnboardingSeed: true },
+  );
+  await page.goto("/");
+  await navigateToSetupPage(page);
+  await page.getByTestId("onboarding-setup-next").click();
+
+  await expect(
+    page.getByText("Couldn't load your existing default harness. Try again."),
+  ).toBeVisible();
+  await expect(page.getByTestId("onboarding-finish")).toBeDisabled();
+  await page.getByTestId("onboarding-finish").click({ force: true });
+  await expect(page.getByTestId("onboarding-page-config")).toBeVisible();
+
+  let saved = await page.evaluate(async () => {
+    return await (
+      window as Window & {
+        __BUZZ_E2E_INVOKE_MOCK_COMMAND__?: (
+          command: string,
+          payload: unknown,
+        ) => Promise<{
+          env_vars: Record<string, string>;
+          model: string | null;
+          preferred_runtime: string | null;
+          provider: string | null;
+        }>;
+      }
+    ).__BUZZ_E2E_INVOKE_MOCK_COMMAND__?.("get_global_agent_config", null);
+  });
+  expect(saved).toMatchObject({
+    env_vars: {
+      ANTHROPIC_API_KEY: "sk-existing",
+      BUZZ_AGENT_THINKING_EFFORT: "high",
+    },
+    model: "claude-sonnet-4",
+    preferred_runtime: "claude",
+    provider: "anthropic",
+  });
+
+  await page.getByRole("button", { name: "Try again" }).click();
+  await expect(page.getByTestId("global-agent-default-harness")).toHaveText(
+    "Claude Code",
+  );
+  const harness = page.getByTestId("global-agent-default-harness");
+  await harness.click();
+  await page.getByTestId("global-agent-default-harness-option-codex").click();
+  await expect(page.getByTestId("onboarding-finish")).toBeEnabled();
+  await page.getByTestId("onboarding-finish").click();
+  await expect(page.getByText("Join or create a community")).toBeVisible();
+
+  saved = await page.evaluate(async () => {
+    return await (
+      window as Window & {
+        __BUZZ_E2E_INVOKE_MOCK_COMMAND__?: (
+          command: string,
+          payload: unknown,
+        ) => Promise<{
+          env_vars: Record<string, string>;
+          model: string | null;
+          preferred_runtime: string | null;
+          provider: string | null;
+        }>;
+      }
+    ).__BUZZ_E2E_INVOKE_MOCK_COMMAND__?.("get_global_agent_config", null);
+  });
+  expect(saved).toMatchObject({
+    env_vars: {
+      ANTHROPIC_API_KEY: "sk-existing",
+    },
+    model: null,
+    preferred_runtime: "codex",
+    provider: null,
+  });
+  expect(saved?.env_vars).not.toHaveProperty("BUZZ_AGENT_THINKING_EFFORT");
+});
+
 test("defaults hides model when optional harness has empty discovery", async ({
   page,
 }) => {
diff --git a/desktop/tests/helpers/bridge.ts b/desktop/tests/helpers/bridge.ts
index ed94e6b176..493017582d 100644
--- a/desktop/tests/helpers/bridge.ts
+++ b/desktop/tests/helpers/bridge.ts
@@ -497,6 +497,8 @@ type MockBridgeOptions = {
     model: string | null;
     preferred_runtime?: string | null;
   };
+  /** Sequenced `get_global_agent_config` failures. Null succeeds; a string throws. */
+  globalAgentConfigErrors?: (string | null)[];
   ownerOnlyAccessBuild?: boolean;
   /** File-layer config returned by runtime id. */
   runtimeFileConfigs?: Record<