feat: apt proxy check+fix as device warning

- get_device_warnings(): checks /etc/apt/apt.conf.d/00proxy on apt systems
  (only when apt_proxy_url is set via optional_args from NetOrk settings)
- _action_fix_apt_proxy(): writes the proxy config via sudo, uses base64 to
  avoid quoting issues
- run_device_action(): routes 'fix_apt_proxy' to the new method

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

napalm_linux/linux.py

@@ -80,6 +80,9 @@ class LinuxDriver(OSDriver):
         self._secret: str = optional_args.get("secret", password)
         # Optional sudo password for privilege escalation (e.g. apt-get update)
         self._sudo_password: Optional[str] = optional_args.get("sudo_password")
+        # Expected apt proxy URL — checked as a device warning on apt systems.
+        # Only set when apt_proxy_enabled=true in NetOrk settings; empty string disables the check.
+        self._apt_proxy_url: str = optional_args.get("apt_proxy_url", "")
 
         if optional_args.get("debugging"):
             logger.setLevel(logging.DEBUG)
@@ -788,6 +791,7 @@ class LinuxDriver(OSDriver):
 
         Currently detects:
         - package updates available (uses local package cache)
+        - apt proxy not configured (apt systems only)
         """
         warnings: List[Dict[str, Any]] = []
         try:
@@ -805,6 +809,18 @@ class LinuxDriver(OSDriver):
                     "packages": [u.get("name", "") for u in updates],
                 },
             })
+        if self._pkg_manager == "apt" and self._apt_proxy_url:
+            try:
+                current = self._send("cat /etc/apt/apt.conf.d/00proxy 2>/dev/null || true").strip()
+                if self._apt_proxy_url not in current:
+                    warnings.append({
+                        "code": "apt_proxy_missing",
+                        "severity": "warning",
+                        "action": "fix_apt_proxy",
+                        "meta": {"expected_url": self._apt_proxy_url},
+                    })
+            except Exception as exc:
+                logger.warning("get_device_warnings: apt proxy check failed: %s", exc)
         return warnings
 
     def _get_updates_apt(self) -> List[UpdateDict]:
@@ -1616,6 +1632,8 @@ class LinuxDriver(OSDriver):
             return self._action_fix_docker_permissions()
         if action == "fix_snmp":
             return self._action_fix_snmp()
+        if action == "fix_apt_proxy":
+            return self._action_fix_apt_proxy()
         raise NotImplementedError(f"Unknown action: {action!r}")
 
     def _action_fix_snmp(self) -> DeviceActionResultDict:
@@ -1750,6 +1768,29 @@ class LinuxDriver(OSDriver):
             out = f"Added {user!r} to the docker group. Reconnect or run a new poll to verify."
         return {"success": success, "output": out}
 
+    def _action_fix_apt_proxy(self) -> DeviceActionResultDict:
+        """Write /etc/apt/apt.conf.d/00proxy with the configured proxy URL."""
+        import base64 as _b64
+        proxy_url = self._apt_proxy_url
+        if not proxy_url:
+            return {"success": False, "output": "No apt_proxy_url configured."}
+        if self._pkg_manager != "apt":
+            return {"success": False, "output": f"Package manager is {self._pkg_manager!r}, not apt — skipping."}
+
+        content = f'Acquire::http::Proxy "{proxy_url}";\n'
+        content_b64 = _b64.b64encode(content.encode()).decode()
+        self._send(f"echo {content_b64} | base64 -d > /tmp/netork_00proxy")
+        self._sudo(
+            "mv /tmp/netork_00proxy /etc/apt/apt.conf.d/00proxy && "
+            "chown root:root /etc/apt/apt.conf.d/00proxy && "
+            "chmod 644 /etc/apt/apt.conf.d/00proxy"
+        )
+        verify = self._send("cat /etc/apt/apt.conf.d/00proxy 2>/dev/null").strip()
+        success = proxy_url in verify
+        if success:
+            return {"success": True, "output": f"Wrote /etc/apt/apt.conf.d/00proxy — proxy: {proxy_url}"}
+        return {"success": False, "output": f"Write may have failed. File content: {verify[:200]}"}
+
     def get_vpn_tunnels(self) -> Dict[str, Any]:
         """Return WireGuard status via ``wg show all dump`` (requires root/sudo).