diff --git a/frontend/src/pages/nodes/NodeFormModal.tsx b/frontend/src/pages/nodes/NodeFormModal.tsx
index 0bb9d73..5aefab0 100644
--- a/frontend/src/pages/nodes/NodeFormModal.tsx
+++ b/frontend/src/pages/nodes/NodeFormModal.tsx
@@ -20,6 +20,7 @@ import type { Msg } from '@/utils';
 import { NodeFormSchema, type NodeFormValues, type ProbeResult } from '@/schemas/node';
 import { FormField, rhfZodValidate } from '@/components/form/rhf';
 import { useOutboundTagGroups } from '@/api/queries/useOutboundTags';
+import { currentPanelMasterUrl } from './agentMasterUrl';
 import './NodeFormModal.css';
 
 type Mode = 'add' | 'edit';
@@ -248,8 +249,10 @@ export default function NodeFormModal({
         if (agentMode && mode === 'add' && obj?.agentToken) {
           setAgentToken(obj.agentToken);
           setAgentNodeName(result.data.name.trim());
-          // Default master URL to the current panel origin; user can edit it.
-          setAgentMasterUrl(window.location.origin);
+          // Default the master URL to the address this panel is being
+          // viewed through — origin AND base path. Dropping the base
+          // path made the agent's registration 404. User can edit it.
+          setAgentMasterUrl(currentPanelMasterUrl());
           // Keep the modal open state; the token dialog shows on top.
         } else {
           onOpenChange(false);
@@ -264,6 +267,13 @@ export default function NodeFormModal({
     if (!submitting) onOpenChange(false);
   }
 
+  // The install command is only meaningful with a master URL; an empty
+  // one would produce a command that can never register, so withhold it
+  // (and say why) instead of letting the user copy a dead command.
+  const installCmd = agentMasterUrl
+    ? `bash <(curl -fL https://git.881218.xyz/rogue/3x-ui-agent/raw/branch/main/install-agent.sh) --master ${agentMasterUrl} --token ${agentToken ?? ''} --name ${agentNodeName}`
+    : '';
+
   return (
     <>
       {messageContextHolder}
@@ -560,9 +570,9 @@ export default function NodeFormModal({
           <Button
             key="copy"
             type="primary"
+            disabled={!installCmd}
             onClick={() => {
-              const cmd = `bash <(curl -fL https://git.881218.xyz/rogue/3x-ui-agent/raw/branch/main/install-agent.sh) --master ${agentMasterUrl} --token ${agentToken} --name ${agentNodeName}`;
-              navigator.clipboard.writeText(cmd).then(
+              navigator.clipboard.writeText(installCmd).then(
                 () => messageApi.success(t('pages.nodes.agentTokenCopied')),
                 () => messageApi.error(t('pages.nodes.agentTokenCopyFailed')),
               );
@@ -597,9 +607,18 @@ export default function NodeFormModal({
           onChange={(e) => setAgentMasterUrl(e.target.value.trim())}
           style={{ marginBottom: 12, fontFamily: 'monospace' }}
         />
+        {!agentMasterUrl && (
+          <Alert
+            type="warning"
+            showIcon
+            style={{ marginBottom: 12 }}
+            title={t('pages.nodes.agentMasterUrlRequired')}
+          />
+        )}
         <p>{t('pages.nodes.agentTokenHint')}</p>
         <Input.TextArea
-          value={`bash <(curl -fL https://git.881218.xyz/rogue/3x-ui-agent/raw/branch/main/install-agent.sh) --master ${agentMasterUrl} --token ${agentToken} --name ${agentNodeName}`}
+          value={installCmd}
+          placeholder={t('pages.nodes.agentMasterUrlRequired')}
           readOnly
           rows={4}
           style={{ fontFamily: 'monospace' }}
diff --git a/frontend/src/pages/nodes/agentMasterUrl.ts b/frontend/src/pages/nodes/agentMasterUrl.ts
new file mode 100644
index 0000000..f437003
--- /dev/null
+++ b/frontend/src/pages/nodes/agentMasterUrl.ts
@@ -0,0 +1,20 @@
+// Default master URL offered in the agent install command.
+//
+// The agent registers against {master_url}/panel/api/agent/register, and
+// the panel itself is usually served under a base path (webBasePath, e.g.
+// "/rogue"). Prefilling the bare origin — as the form used to — produced
+// an install command whose registration 404'd, leaving the node stuck at
+// "unknown" on the panel. The address the operator is viewing the panel
+// through already contains the base path, so derive the default from it:
+// origin + window.X_UI_BASE_PATH (injected by the panel server). The
+// operator can still override it (e.g. a public address instead of a LAN
+// or tunnel one).
+export function computeDefaultMasterUrl(origin: string, basePath: string | undefined): string {
+  const trimmed = (basePath || '/').replace(/\/+$/, '');
+  return origin + trimmed;
+}
+
+export function currentPanelMasterUrl(): string {
+  if (typeof window === 'undefined') return '';
+  return computeDefaultMasterUrl(window.location.origin, window.X_UI_BASE_PATH);
+}
diff --git a/frontend/src/test/agent-master-url.test.ts b/frontend/src/test/agent-master-url.test.ts
new file mode 100644
index 0000000..67e9f0f
--- /dev/null
+++ b/frontend/src/test/agent-master-url.test.ts
@@ -0,0 +1,33 @@
+import { describe, expect, it } from 'vitest';
+
+import { computeDefaultMasterUrl } from '@/pages/nodes/agentMasterUrl';
+
+// The install command's --master must be the address agents can register
+// against: origin + panel base path. Dropping the base path was the
+// production bug — registration 404'd and the node stayed "unknown".
+describe('computeDefaultMasterUrl', () => {
+  it('keeps a base path with trailing slash', () => {
+    expect(computeDefaultMasterUrl('https://amb.example.com', '/rogue/')).toBe(
+      'https://amb.example.com/rogue',
+    );
+  });
+
+  it('keeps a base path without trailing slash', () => {
+    expect(computeDefaultMasterUrl('https://amb.example.com', '/rogue')).toBe(
+      'https://amb.example.com/rogue',
+    );
+  });
+
+  it('root base path yields the bare origin', () => {
+    expect(computeDefaultMasterUrl('http://192.168.0.1:55889', '/')).toBe('http://192.168.0.1:55889');
+  });
+
+  it('undefined or empty base path yields the bare origin', () => {
+    expect(computeDefaultMasterUrl('http://10.0.0.2:2053', undefined)).toBe('http://10.0.0.2:2053');
+    expect(computeDefaultMasterUrl('http://10.0.0.2:2053', '')).toBe('http://10.0.0.2:2053');
+  });
+
+  it('nested base paths survive', () => {
+    expect(computeDefaultMasterUrl('https://example.com', '/a/b/')).toBe('https://example.com/a/b');
+  });
+});
diff --git a/internal/web/translation/ar-EG.json b/internal/web/translation/ar-EG.json
index 7bf041b..08210c5 100644
--- a/internal/web/translation/ar-EG.json
+++ b/internal/web/translation/ar-EG.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "افتراضي",
diff --git a/internal/web/translation/en-US.json b/internal/web/translation/en-US.json
index 3c8a39f..4256661 100644
--- a/internal/web/translation/en-US.json
+++ b/internal/web/translation/en-US.json
@@ -1061,7 +1061,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "Default",
diff --git a/internal/web/translation/es-ES.json b/internal/web/translation/es-ES.json
index a5f4042..0a349d9 100644
--- a/internal/web/translation/es-ES.json
+++ b/internal/web/translation/es-ES.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "Predeterminado",
diff --git a/internal/web/translation/fa-IR.json b/internal/web/translation/fa-IR.json
index a8ee9ac..1e48127 100644
--- a/internal/web/translation/fa-IR.json
+++ b/internal/web/translation/fa-IR.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "پیش‌فرض",
diff --git a/internal/web/translation/id-ID.json b/internal/web/translation/id-ID.json
index 38e43ee..860327a 100644
--- a/internal/web/translation/id-ID.json
+++ b/internal/web/translation/id-ID.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "Bawaan",
diff --git a/internal/web/translation/ja-JP.json b/internal/web/translation/ja-JP.json
index cfbf3e0..073136a 100644
--- a/internal/web/translation/ja-JP.json
+++ b/internal/web/translation/ja-JP.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "デフォルト",
diff --git a/internal/web/translation/pt-BR.json b/internal/web/translation/pt-BR.json
index ca8ddaa..7047f44 100644
--- a/internal/web/translation/pt-BR.json
+++ b/internal/web/translation/pt-BR.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "Padrão",
diff --git a/internal/web/translation/ru-RU.json b/internal/web/translation/ru-RU.json
index cba978c..78ba7c3 100644
--- a/internal/web/translation/ru-RU.json
+++ b/internal/web/translation/ru-RU.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "По умолчанию",
diff --git a/internal/web/translation/tr-TR.json b/internal/web/translation/tr-TR.json
index 30dd09b..75e0450 100644
--- a/internal/web/translation/tr-TR.json
+++ b/internal/web/translation/tr-TR.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "Varsayılan",
diff --git a/internal/web/translation/uk-UA.json b/internal/web/translation/uk-UA.json
index 9366970..b0e4ed2 100644
--- a/internal/web/translation/uk-UA.json
+++ b/internal/web/translation/uk-UA.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "Типово",
diff --git a/internal/web/translation/vi-VN.json b/internal/web/translation/vi-VN.json
index 507ca6b..29f35e5 100644
--- a/internal/web/translation/vi-VN.json
+++ b/internal/web/translation/vi-VN.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "Mặc định",
diff --git a/internal/web/translation/zh-CN.json b/internal/web/translation/zh-CN.json
index 3c844d7..dd798da 100644
--- a/internal/web/translation/zh-CN.json
+++ b/internal/web/translation/zh-CN.json
@@ -943,7 +943,8 @@
       "agentTokenCopied": "安装命令已复制",
       "agentTokenCopyFailed": "复制失败，请手动复制",
       "copyToken": "复制安装命令",
-      "agentMasterUrlHint": "主控地址（agent 用来连接主控，如有域名或反代请改成对外地址）："
+      "agentMasterUrlHint": "主控地址（agent 用来连接主控，如有域名或反代请改成对外地址）：",
+      "agentMasterUrlRequired": "主控地址为空——请先填入主控地址，之后才会生成安装命令。"
     },
     "settings": {
       "defaultTag": "默认",
diff --git a/internal/web/translation/zh-TW.json b/internal/web/translation/zh-TW.json
index a95031c..36061c1 100644
--- a/internal/web/translation/zh-TW.json
+++ b/internal/web/translation/zh-TW.json
@@ -921,7 +921,8 @@
       "agentTokenCopied": "Install command copied",
       "agentTokenCopyFailed": "Copy failed, please copy manually",
       "copyToken": "Copy Install Command",
-      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):"
+      "agentMasterUrlHint": "Master URL (used by agent to reach the master; change to public address if behind proxy):",
+      "agentMasterUrlRequired": "Master URL is empty — enter the master address first; the install command is generated only then."
     },
     "settings": {
       "defaultTag": "預設",