diff --git a/src/agents/sandbox.resolveSandboxContext.test.ts b/src/agents/sandbox.resolveSandboxContext.test.ts
index 64b318b3729..c75b8ac4c19 100644
--- a/src/agents/sandbox.resolveSandboxContext.test.ts
+++ b/src/agents/sandbox.resolveSandboxContext.test.ts
@@ -101,6 +101,58 @@ describe("resolveSandboxContext", () => {
     expect(result).toBeNull();
   }, 15_000);
 
+  it("does not touch sandbox backends for cron or sub-agent sessions when sandbox mode is off", async () => {
+    const backendFactory = vi.fn(async () => ({
+      id: "test-off-backend",
+      runtimeId: "unexpected-runtime",
+      runtimeLabel: "Unexpected Runtime",
+      workdir: "/workspace",
+      buildExecSpec: async () => ({
+        argv: ["unexpected"],
+        env: process.env,
+        stdinMode: "pipe-closed" as const,
+      }),
+      runShellCommand: async () => ({
+        stdout: Buffer.alloc(0),
+        stderr: Buffer.alloc(0),
+        code: 0,
+      }),
+    }));
+    const restore = registerSandboxBackend("test-off-backend", backendFactory);
+    try {
+      const cfg: OpenClawConfig = {
+        agents: {
+          defaults: {
+            sandbox: {
+              mode: "off",
+              backend: "test-off-backend",
+              scope: "session",
+            },
+          },
+        },
+      };
+
+      await expect(
+        resolveSandboxContext({
+          config: cfg,
+          sessionKey: "agent:main:cron:job:run:uuid",
+          workspaceDir: "/tmp/openclaw-test",
+        }),
+      ).resolves.toBeNull();
+      await expect(
+        resolveSandboxContext({
+          config: cfg,
+          sessionKey: "agent:main:subagent:child",
+          workspaceDir: "/tmp/openclaw-test",
+        }),
+      ).resolves.toBeNull();
+
+      expect(backendFactory).not.toHaveBeenCalled();
+    } finally {
+      restore();
+    }
+  }, 15_000);
+
   it("treats main session aliases as main in non-main mode", async () => {
     const cfg: OpenClawConfig = {
       session: { mainKey: "work" },
diff --git a/src/agents/sandbox/browser.create.test.ts b/src/agents/sandbox/browser.create.test.ts
index ea7e515b037..117f5db9b6b 100644
--- a/src/agents/sandbox/browser.create.test.ts
+++ b/src/agents/sandbox/browser.create.test.ts
@@ -236,6 +236,34 @@ describe("ensureSandboxBrowser create args", () => {
     expect(result?.noVncUrl).toBeUndefined();
   });
 
+  it("fails before creating a browser container when Docker daemon is unavailable", async () => {
+    dockerMocks.execDocker.mockImplementation(async (args: string[]) => {
+      if (args[0] === "network" && args[1] === "inspect") {
+        return { stdout: "", stderr: "", code: 0 };
+      }
+      if (args[0] === "image" && args[1] === "inspect") {
+        return {
+          stdout: "",
+          stderr:
+            "Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?",
+          code: 1,
+        };
+      }
+      return { stdout: "", stderr: "", code: 0 };
+    });
+
+    await expect(
+      ensureTestSandboxBrowser({
+        scopeKey: "session:test",
+        workspaceDir: "/tmp/workspace",
+        agentWorkspaceDir: "/tmp/workspace",
+        cfg: buildConfig(false),
+      }),
+    ).rejects.toThrow("Docker daemon is not available");
+
+    expect(findDockerArgsCall(dockerMocks.execDocker.mock.calls, "create")).toBeUndefined();
+  });
+
   it("passes the browser SSRF policy to the sandbox bridge", async () => {
     await ensureTestSandboxBrowser({
       scopeKey: "session:test",
diff --git a/src/agents/sandbox/browser.ts b/src/agents/sandbox/browser.ts
index dac3f84d17c..fe24e25850b 100644
--- a/src/agents/sandbox/browser.ts
+++ b/src/agents/sandbox/browser.ts
@@ -26,6 +26,7 @@ import {
   buildSandboxCreateArgs,
   dockerContainerState,
   execDocker,
+  formatDockerDaemonUnavailableError,
   isDockerDaemonUnavailable,
   readDockerContainerEnvVar,
   readDockerContainerLabel,
@@ -132,10 +133,8 @@ async function ensureSandboxBrowserImage(image: string) {
     return;
   }
   const stderr = result.stderr.trim();
-  // When Docker daemon is unavailable, silently return instead of throwing.
-  // This allows sandbox.mode="off" sessions to start without Docker errors.
   if (isDockerDaemonUnavailable(stderr)) {
-    return;
+    throw new Error(formatDockerDaemonUnavailableError(stderr));
   }
   throw new Error(
     `Sandbox browser image not found: ${image}. Build it with scripts/sandbox-browser-setup.sh.`,
diff --git a/src/agents/sandbox/docker.test.ts b/src/agents/sandbox/docker.test.ts
index 2cae9429137..87a8a2b7d90 100644
--- a/src/agents/sandbox/docker.test.ts
+++ b/src/agents/sandbox/docker.test.ts
@@ -118,12 +118,14 @@ describe("ensureDockerImage", () => {
     ]);
   });
 
-  it("returns when the Docker daemon is unavailable during image inspection", async () => {
+  it("throws when the Docker daemon is unavailable during image inspection", async () => {
     spawnState.imageExists = false;
     spawnState.inspectError =
       "Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?";
 
-    await ensureDockerImage(DEFAULT_SANDBOX_IMAGE);
+    await expect(ensureDockerImage(DEFAULT_SANDBOX_IMAGE)).rejects.toThrow(
+      "Docker daemon is not available",
+    );
 
     expect(spawnState.calls).toEqual([
       {
diff --git a/src/agents/sandbox/docker.ts b/src/agents/sandbox/docker.ts
index 6d9eca9865e..24ed82b520a 100644
--- a/src/agents/sandbox/docker.ts
+++ b/src/agents/sandbox/docker.ts
@@ -283,7 +283,18 @@ export function isDockerDaemonUnavailable(stderr: string): boolean {
   return DOCKER_DAEMON_UNAVAILABLE_MARKERS.some((marker) => stderr.toLowerCase().includes(marker));
 }
 
-async function inspectDockerImage(image: string): Promise<"exists" | "missing" | "unavailable"> {
+export function formatDockerDaemonUnavailableError(stderr: string): string {
+  const detail = stderr.trim();
+  return [
+    "Sandbox mode requires Docker, but the Docker daemon is not available.",
+    "Start Docker, or set `agents.defaults.sandbox.mode=off` to disable sandboxing.",
+    detail ? `Docker said: ${detail}` : undefined,
+  ]
+    .filter((line): line is string => Boolean(line))
+    .join(" ");
+}
+
+async function inspectDockerImage(image: string): Promise<"exists" | "missing"> {
   const result = await execDocker(["image", "inspect", image], {
     allowFailure: true,
   });
@@ -294,18 +305,15 @@ async function inspectDockerImage(image: string): Promise<"exists" | "missing" |
   if (stderr.toLowerCase().includes("no such image")) {
     return "missing";
   }
-  // When Docker daemon is unavailable, treat the image as unavailable
-  // rather than throwing. This allows sandbox.mode="off" sessions to
-  // start without a running Docker daemon.
   if (isDockerDaemonUnavailable(stderr)) {
-    return "unavailable";
+    throw new Error(formatDockerDaemonUnavailableError(stderr));
   }
   throw new Error(`Failed to inspect sandbox image: ${stderr}`);
 }
 
 export async function ensureDockerImage(image: string) {
   const imageState = await inspectDockerImage(image);
-  if (imageState === "exists" || imageState === "unavailable") {
+  if (imageState === "exists") {
     return;
   }
   if (image === DEFAULT_SANDBOX_IMAGE) {