diff --git a/src/lib/build-context.test.ts b/src/lib/build-context.test.ts
index 41516f5c9e3..897c13e7305 100644
--- a/src/lib/build-context.test.ts
+++ b/src/lib/build-context.test.ts
@@ -203,6 +203,25 @@ describe("printSandboxCreateRecoveryHints", () => {
     expect(out).toContain("NEMOCLAW_SANDBOX_GPU=0");
     expect(out).toContain("onboard --resume --no-gpu");
   });
+
+  it("prints plugin-install network-policy guidance when the Docker build fails at the OpenClaw plugin install step", () => {
+    const output = [
+      "npm error code ENOTFOUND",
+      "npm error network request to https://registry.npmjs.org/@openclaw%2Fbrave-plugin failed, reason: getaddrinfo ENOTFOUND registry.npmjs.org",
+      "Docker stream error: The command '/bin/bash -o pipefail -c set -eu;",
+      '  openclaw plugins install "npm:@openclaw/brave-plugin@2026.5.27" --pin;',
+      "fi' returned a non-zero code: 1",
+    ].join("\n");
+    printSandboxCreateRecoveryHints(output);
+
+    const out = stderr();
+    expect(out).toContain("OpenClaw plugin-install step");
+    expect(out).toContain("ClawHub");
+    expect(out).toContain("npm registry");
+    expect(out).toContain("network policy");
+    expect(out).toContain("NEMOCLAW_WEB_SEARCH_ENABLED=0");
+    expect(out).toContain("onboard --resume");
+  });
 });
 
 describe("reconstructImageRefCreateCommand", () => {
diff --git a/src/lib/build-context.ts b/src/lib/build-context.ts
index 4e70a771522..8eaffffa872 100644
--- a/src/lib/build-context.ts
+++ b/src/lib/build-context.ts
@@ -218,6 +218,21 @@ export function printSandboxCreateRecoveryHints(
     console.error(`  Recovery: ${CLI_NAME} onboard --resume --no-gpu`);
     return;
   }
+  if (failure.kind === "plugin_install_network_denied") {
+    console.error("  Hint: The sandbox Docker build failed at the OpenClaw plugin-install step.");
+    console.error(
+      "        Could not reach ClawHub or the npm registry — your sandbox network policy",
+    );
+    console.error(
+      "        may be blocking outbound plugin-install access. Check whether an active",
+    );
+    console.error("        preset allows egress to the npm registry and ClawHub, or disable the");
+    console.error(
+      "        feature that requires this plugin (e.g. NEMOCLAW_WEB_SEARCH_ENABLED=0).",
+    );
+    console.error(`  Recovery: ${CLI_NAME} onboard --resume`);
+    return;
+  }
   console.error(`  Recovery: ${CLI_NAME} onboard --resume`);
   console.error(`  Or:      ${CLI_NAME} onboard`);
 }
diff --git a/src/lib/validation-plugin-install.test.ts b/src/lib/validation-plugin-install.test.ts
new file mode 100644
index 00000000000..3a2ee8c3621
--- /dev/null
+++ b/src/lib/validation-plugin-install.test.ts
@@ -0,0 +1,108 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+import { describe, expect, it } from "vitest";
+
+import { classifySandboxCreateFailure } from "./validation";
+
+describe("classifySandboxCreateFailure plugin-install network arm", () => {
+  it("detects plugin install network denial from ENOTFOUND against the npm registry", () => {
+    const output = [
+      "npm error code ENOTFOUND",
+      "npm error errno ENOTFOUND",
+      "npm error network request to https://registry.npmjs.org/@openclaw%2Fbrave-plugin failed, reason: getaddrinfo ENOTFOUND registry.npmjs.org",
+      "Docker stream error: The command '/bin/bash -o pipefail -c set -eu;",
+      '  openclaw plugins install "npm:@openclaw/brave-plugin@2026.5.27" --pin;',
+      "  BRAVE_API_KEY=openshell:resolve:env:BRAVE_API_KEY openclaw doctor --fix --non-interactive;",
+      "fi' returned a non-zero code: 1",
+    ].join("\n");
+    const result = classifySandboxCreateFailure(output);
+    expect(result.kind).toBe("plugin_install_network_denied");
+    expect(result.uploadedToGateway).toBe(false);
+  });
+
+  it("detects plugin install network denial from ECONNREFUSED against ClawHub", () => {
+    const output = [
+      "npm error code ECONNREFUSED",
+      "npm error network request to https://registry.clawhub.io/@openclaw%2Fdiagnostics-otel failed, reason: connect ECONNREFUSED 34.120.54.1:443",
+      "The command '...openclaw plugins install npm:@openclaw/diagnostics-otel@2026.5.27 --pin...' returned a non-zero code: 1",
+    ].join("\n");
+    expect(classifySandboxCreateFailure(output).kind).toBe("plugin_install_network_denied");
+  });
+
+  it("does NOT classify unrelated failures as plugin_install_network_denied", () => {
+    expect(classifySandboxCreateFailure("npm install failed with ENOENT").kind).toBe("unknown");
+    expect(classifySandboxCreateFailure("openclaw doctor --fix failed").kind).toBe("unknown");
+  });
+
+  it("does NOT classify as plugin_install_network_denied when plugin install fails for a non-network reason", () => {
+    const output = [
+      "npm error code E404",
+      "npm error 404 Not Found - GET https://registry.npmjs.org/@openclaw%2Fmissing-plugin",
+      "npm error 404 '@openclaw/missing-plugin@0.0.0' is not in the npm registry",
+      "The command '/bin/bash -c openclaw plugins install npm:@openclaw/missing-plugin@0.0.0 --pin' returned a non-zero code: 1",
+    ].join("\n");
+    expect(classifySandboxCreateFailure(output).kind).toBe("unknown");
+  });
+
+  it("does NOT classify as plugin_install_network_denied when plugin install step succeeded and a later step failed", () => {
+    const output = [
+      "Step 3/10 : RUN openclaw plugins install npm:@openclaw/brave-plugin@2026.5.27 --pin",
+      " ---> Running in abc123",
+      " ---> def456",
+      "Step 4/10 : RUN fail-step",
+      " ---> Running in xyz789",
+      "The command '/bin/sh -c fail-step' returned a non-zero code: 1",
+    ].join("\n");
+    expect(classifySandboxCreateFailure(output).kind).toBe("unknown");
+  });
+
+  it("does NOT classify as plugin_install_network_denied when plugin install succeeded but a later command in the same RUN block failed with a network error", () => {
+    // The same RUN block runs `openclaw plugins install` followed by
+    // `openclaw doctor --fix`. If the install succeeds but doctor's network
+    // call fails, the block fails but npm never emits an "npm error" line,
+    // so the classifier must not fire the plugin-install hint.
+    const output = [
+      "The command '/bin/bash -o pipefail -c set -eu;",
+      '  openclaw plugins install "npm:@openclaw/brave-plugin@2026.5.27" --pin;',
+      "  BRAVE_API_KEY=openshell:resolve:env:BRAVE_API_KEY openclaw doctor --fix --non-interactive;",
+      "fi' returned a non-zero code: 1",
+      "error: getaddrinfo ENOTFOUND api.openclaw.ai",
+    ].join("\n");
+    expect(classifySandboxCreateFailure(output).kind).toBe("unknown");
+  });
+
+  it("does NOT classify as plugin_install_network_denied when an npm script after the plugin install in the same RUN block emits a network npm error", () => {
+    // If `openclaw plugins install` succeeds but a later npm-based command in
+    // the same RUN block fails, its stderr appears before Docker's final failed-
+    // command summary. Correlating the error URL to the requested plugin keeps
+    // the unrelated package failure on the generic recovery path.
+    const output = [
+      "npm error code ENOTFOUND",
+      "npm error network request to https://registry.npmjs.org/@openclaw%2Ftools failed, reason: getaddrinfo ENOTFOUND registry.npmjs.org",
+      "The command '/bin/bash -o pipefail -c set -eu;",
+      '  openclaw plugins install "npm:@openclaw/brave-plugin@2026.5.27" --pin;',
+      "  npm run doctor-fix;",
+      "fi' returned a non-zero code: 1",
+    ].join("\n");
+    expect(classifySandboxCreateFailure(output).kind).toBe("unknown");
+  });
+
+  it("does NOT classify package-agnostic npm network output as a plugin install denial", () => {
+    const output = [
+      "npm error code ENOTFOUND",
+      "npm error network request to https://registry.npmjs.org failed, reason: getaddrinfo ENOTFOUND registry.npmjs.org",
+      "The command '/bin/bash -c openclaw plugins install npm:@openclaw/brave-plugin@2026.5.27 --pin' returned a non-zero code: 1",
+    ].join("\n");
+    expect(classifySandboxCreateFailure(output).kind).toBe("unknown");
+  });
+
+  it("does NOT classify a non-plugin command that names the same scoped package", () => {
+    const output = [
+      "npm error code ENOTFOUND",
+      "npm error network request to https://registry.npmjs.org/@openclaw%2Ftools failed, reason: getaddrinfo ENOTFOUND registry.npmjs.org",
+      "The command '/bin/sh -c npm install npm:@openclaw/tools' returned a non-zero code: 1",
+    ].join("\n");
+    expect(classifySandboxCreateFailure(output).kind).toBe("unknown");
+  });
+});
diff --git a/src/lib/validation.ts b/src/lib/validation.ts
index 03ab1b3b90a..ab071a1c2bb 100644
--- a/src/lib/validation.ts
+++ b/src/lib/validation.ts
@@ -20,6 +20,7 @@ export interface SandboxCreateFailure {
     | "sandbox_create_incomplete"
     | "tls_cert_mismatch"
     | "gpu_cdi_injection_failed"
+    | "plugin_install_network_denied"
     | "unknown";
   uploadedToGateway: boolean;
 }
@@ -134,6 +135,48 @@ export function classifySandboxCreateFailure(output = ""): SandboxCreateFailure
   ) {
     return { kind: "gpu_cdi_injection_failed", uploadedToGateway };
   }
+  // Require BOTH the failed Docker command block containing the plugin-install
+  // step AND npm-prefixed network evidence for the same plugin package. Docker
+  // prints subprocess stderr before its final failed-command summary, so a
+  // prefix-only search can misattribute a later npm command in the same RUN
+  // block. Package correlation keeps that failure on the generic recovery path.
+  // OpenShell exposes only combined Docker text here, so this classifier is the
+  // source boundary until callers can consume a structured plugin-install
+  // failure with package identity; remove the text classifier at that point.
+  // In JavaScript, [^'] matches every character except a single quote,
+  // including newlines (unlike `.` without the dotAll flag), so multi-line
+  // command text is handled correctly. See #4127 / follow-up from #4125.
+  const pluginInstallErrorMatch =
+    /The command '[^']*openclaw plugins install[^']*'\s*returned a non-zero code/i.exec(text);
+  if (pluginInstallErrorMatch) {
+    const segment = text.slice(
+      0,
+      pluginInstallErrorMatch.index + pluginInstallErrorMatch[0].length,
+    );
+    const pluginPackages = [
+      ...pluginInstallErrorMatch[0].matchAll(/(?:npm:)?(@openclaw\/[a-z0-9._-]+)/gi),
+    ].map((match) => match[1].toLowerCase());
+    const npmErrorText = segment
+      .split(/\r?\n/)
+      .filter((line) => /^\s*npm error\b/i.test(line))
+      .join("\n")
+      .toLowerCase();
+    // npm output may print the scoped-package slash literally or percent-
+    // encoded. Normalize comparisons to lowercase so %2F and %2f both match.
+    const hasMatchingPluginPackage = pluginPackages.some((packageName) =>
+      [packageName, packageName.replaceAll("/", "%2f"), encodeURIComponent(packageName)].some(
+        (candidate) => npmErrorText.includes(candidate.toLowerCase()),
+      ),
+    );
+    if (
+      hasMatchingPluginPackage &&
+      /npm error.*(?:ENOTFOUND|EAI_AGAIN|ECONNREFUSED|ETIMEDOUT|ESOCKETTIMEDOUT|network request.*failed|getaddrinfo|fetch failed|socket hang up|network timeout)/i.test(
+        npmErrorText,
+      )
+    ) {
+      return { kind: "plugin_install_network_denied", uploadedToGateway };
+    }
+  }
   if (/Created sandbox:/i.test(text)) {
     return { kind: "sandbox_create_incomplete", uploadedToGateway: true };
   }