docs: split examples into read-only basic and guarded smoke

The previous examples/basic.py ran destructive operations (configure_set,
configure_delete, generate, reset, config_file_load) by default.  That is
not what a public 'basic' example should do.

- examples/basic.py: rewritten as a read-only example
  (retrieve_show_config, show, retrieve_return_values), uses a robust
  env-bool parser, prints response.result via a small helper, and uses
  the supported public import 'from pyvyos import ApiResponse, VyDevice'.
- examples/integration_smoke.py: renamed from the old basic.py, keeps
  the mutating operations, and refuses to run unless
  PYVYOS_ALLOW_MUTATING_EXAMPLE=1 is set.
- README: link both examples and describe what each one does.

Note: the dev/ note about a future Docker-based e2e harness is tracked
in the unreleased issue drafts; it is not part of this release.

2 files changed, 135 insertions, 50 deletions

diff --git a/examples/basic.py b/examples/basic.py
index c133d41..1e1b552 100644
--- a/examples/basic.py
+++ b/examples/basic.py
@@ -1,85 +1,65 @@
-"""Basic pyvyos usage example.
+"""Basic read-only pyvyos usage example.
 
-Run with environment variables loaded from a .env file (see ../.env.example)
-or exported in your shell:
+Run with environment variables loaded from a .env file or exported in your
+shell:
 
     VYDEVICE_HOSTNAME=192.0.2.1 \\
     VYDEVICE_APIKEY=secret \\
     python examples/basic.py
+
+This example only runs read-only commands.
 """
 
 import os
 import pprint
-import random
-import string
 
 from dotenv import load_dotenv
 
-from pyvyos import VyDevice
+from pyvyos import ApiResponse, VyDevice
 
 load_dotenv()
 
 
+def env_bool(name: str, default: str = "true") -> bool:
+    return os.environ.get(name, default).lower() in ("1", "true", "yes")
+
+
 def make_device() -> VyDevice:
     return VyDevice(
         hostname=os.environ["VYDEVICE_HOSTNAME"],
         apikey=os.environ["VYDEVICE_APIKEY"],
         port=int(os.environ.get("VYDEVICE_PORT", "443")),
         protocol=os.environ.get("VYDEVICE_PROTOCOL", "https"),
-        verify=os.environ.get("VYDEVICE_VERIFY_SSL", "true").lower() == "true",
-        timeout=60,
+        verify=env_bool("VYDEVICE_VERIFY_SSL"),
+        timeout=int(os.environ.get("VYDEVICE_TIMEOUT", "60")),
     )
 
 
+def print_response(label: str, response: ApiResponse) -> None:
+    print(f"\n== {label} ==")
+    if response.error:
+        print(f"Error {response.status}: {response.error}")
+        return
+
+    pprint.pprint(response.result)
+
+
 def main() -> None:
     device = make_device()
 
-    # Retrieve the running configuration for the system tree.
-    pprint.pprint(device.retrieve_show_config(path=["system"]))
-
-    # Configure a dummy interface, read it back, then delete it.
-    pprint.pprint(
-        device.configure_set(
-            path=["interfaces", "dummy", "dum1", "address", "192.168.56.100/24"]
-        )
+    print_response(
+        "Running system configuration",
+        device.retrieve_show_config(path=["system"]),
     )
-    pprint.pprint(
-        device.retrieve_return_values(
-            path=["interfaces", "dummy", "dum1", "address"]
-        )
-    )
-    pprint.pprint(device.configure_delete(path=["interfaces", "dummy", "dum1"]))
 
-    # Generate a one-shot SSH client key.
-    randstring = "".join(
-        random.choice(string.ascii_letters + string.digits) for _ in range(20)
-    )
-    pprint.pprint(
-        device.generate(path=["ssh", "client-key", f"/tmp/key_{randstring}"])
+    print_response(
+        "System images",
+        device.show(path=["system", "image"]),
     )
 
-    # Operational commands.
-    pprint.pprint(device.show(path=["system", "image"]))
-    pprint.pprint(device.reset(path=["conntrack-sync", "internal-cache"]))
-
-    # Save and reload the running configuration to/from a file on the device.
-    pprint.pprint(device.config_file_save(file="/config/test300.config"))
-    pprint.pprint(device.config_file_load(file="/config/test300.config"))
-
-    # Batch multiple configuration operations in a single request.
-    pprint.pprint(
-        device.configure_multiple_op(
-            op_path=[
-                {
-                    "op": "set",
-                    "path": [
-                        "interfaces", "dummy", "dum1", "address",
-                        "192.168.56.100/24",
-                    ],
-                },
-                {"op": "delete", "path": ["interfaces", "dummy", "dum1"]},
-            ]
-        )
+    print_response(
+        "Interface address values",
+        device.retrieve_return_values(path=["interfaces"]),
     )
 
 
diff --git a/examples/integration_smoke.py b/examples/integration_smoke.py
new file mode 100644
index 0000000..137ca9b
--- /dev/null
+++ b/examples/integration_smoke.py
@@ -0,0 +1,105 @@
+"""Integration smoke test for pyvyos.
+
+This script changes configuration on the target VyOS device and should only
+be used against a disposable lab device, such as the one provided by
+``examples/vagrant/``.
+
+It may create and delete dummy interfaces, generate temporary files on the
+device, and save/load configuration files.
+
+Run only against a lab device::
+
+    PYVYOS_ALLOW_MUTATING_EXAMPLE=1 \\
+    VYDEVICE_HOSTNAME=127.0.0.1 \\
+    VYDEVICE_APIKEY=secret \\
+    python examples/integration_smoke.py
+"""
+
+import os
+import pprint
+import random
+import string
+import sys
+
+from dotenv import load_dotenv
+
+from pyvyos import VyDevice
+
+load_dotenv()
+
+
+def env_bool(name: str, default: str = "true") -> bool:
+    return os.environ.get(name, default).lower() in ("1", "true", "yes")
+
+
+def make_device() -> VyDevice:
+    return VyDevice(
+        hostname=os.environ["VYDEVICE_HOSTNAME"],
+        apikey=os.environ["VYDEVICE_APIKEY"],
+        port=int(os.environ.get("VYDEVICE_PORT", "443")),
+        protocol=os.environ.get("VYDEVICE_PROTOCOL", "https"),
+        verify=env_bool("VYDEVICE_VERIFY_SSL"),
+        timeout=int(os.environ.get("VYDEVICE_TIMEOUT", "60")),
+    )
+
+
+def main() -> None:
+    if os.environ.get("PYVYOS_ALLOW_MUTATING_EXAMPLE") != "1":
+        sys.exit(
+            "This example mutates the target device. "
+            "Set PYVYOS_ALLOW_MUTATING_EXAMPLE=1 to run it."
+        )
+
+    device = make_device()
+
+    # Retrieve the running configuration for the system tree.
+    pprint.pprint(device.retrieve_show_config(path=["system"]))
+
+    # Configure a dummy interface, read it back, then delete it.
+    pprint.pprint(
+        device.configure_set(
+            path=["interfaces", "dummy", "dum1", "address", "192.168.56.100/24"]
+        )
+    )
+    pprint.pprint(
+        device.retrieve_return_values(
+            path=["interfaces", "dummy", "dum1", "address"]
+        )
+    )
+    pprint.pprint(device.configure_delete(path=["interfaces", "dummy", "dum1"]))
+
+    # Generate a one-shot SSH client key.
+    randstring = "".join(
+        random.choice(string.ascii_letters + string.digits) for _ in range(20)
+    )
+    pprint.pprint(
+        device.generate(path=["ssh", "client-key", f"/tmp/key_{randstring}"])
+    )
+
+    # Operational commands.
+    pprint.pprint(device.show(path=["system", "image"]))
+    pprint.pprint(device.reset(path=["conntrack-sync", "internal-cache"]))
+
+    # Save and reload the running configuration to/from a file on the device.
+    pprint.pprint(device.config_file_save(file="/config/test300.config"))
+    pprint.pprint(device.config_file_load(file="/config/test300.config"))
+
+    # Batch multiple configuration operations in a single request.
+    pprint.pprint(
+        device.configure_multiple_op(
+            op_path=[
+                {
+                    "op": "set",
+                    "path": [
+                        "interfaces", "dummy", "dum1", "address",
+                        "192.168.56.100/24",
+                    ],
+                },
+                {"op": "delete", "path": ["interfaces", "dummy", "dum1"]},
+            ]
+        )
+    )
+
+
+if __name__ == "__main__":
+    main()