feat: make the docker binary path a hook

Where docker lives is device-specific; what to do with it is not. QNAP's
Container Station installs docker under /share/<pool>/.qpkg/ and never
puts it on PATH, so a QTS driver inheriting this class found no docker at
all.

Rather than reimplementing the Docker surface in the vendor driver, the
path becomes a single overridable method and every call site goes through
it. Per docs/ARCHITECTURE.md 4.4, generic logic belongs to the shared
driver and only the device-specific mechanics belong to the vendor one.

A test asserts that *every* docker call site uses the hook — a half
converted set would let detection find the binary while the actual
queries still missed it, which only shows up against real hardware.

napalm_linux/linux.py

@@ -1480,6 +1480,16 @@ class LinuxDriver(OSDriver):
     # Docker
     # ------------------------------------------------------------------
 
+    def _docker_bin(self) -> str:
+        """Path to the docker binary.
+
+        A hook rather than a literal because the Docker *logic* is the same
+        everywhere while the *location* is not: QTS ships Container Station's
+        docker under /share/<pool>/.qpkg/ and never puts it on PATH. Subclasses
+        override this one method instead of reimplementing the surface.
+        """
+        return "docker"
+
     def get_docker_info(self) -> DockerInfoDict:
         """Return information about the local Docker environment.
 
@@ -1498,26 +1508,28 @@ class LinuxDriver(OSDriver):
         """
         import json as _json
 
+        docker = self._docker_bin()
+
         # Check docker binary first (docker --version doesn't need socket access)
-        if not self._send("command -v docker 2>/dev/null").strip():
+        if not self._send(f"command -v {docker} 2>/dev/null").strip():
             return {"available": False}
 
         # Verify socket access — docker ps is cheaper and fails immediately on permission errors
-        ps_check = self._send("docker ps 2>&1")
+        ps_check = self._send(f"{docker} ps 2>&1")
         if "permission denied" in ps_check.lower() or "cannot connect" in ps_check.lower():
             return {"available": False, "permission_denied": True}
 
-        version = self._send("docker --version 2>/dev/null").strip()
+        version = self._send(f"{docker} --version 2>/dev/null").strip()
 
         combined = self._send(
             "echo '---CONTAINERS---'; "
-            "docker ps -a --format '{{json .}}' 2>/dev/null; "
+            f"{docker} ps -a --format '{{{{json .}}}}' 2>/dev/null; "
             "echo '---IMAGES---'; "
-            "docker images --format '{{json .}}' 2>/dev/null; "
+            f"{docker} images --format '{{{{json .}}}}' 2>/dev/null; "
             "echo '---VOLUMES---'; "
-            "docker volume ls --format '{{json .}}' 2>/dev/null; "
+            f"{docker} volume ls --format '{{{{json .}}}}' 2>/dev/null; "
             "echo '---NETWORKS---'; "
-            "docker network ls --format '{{json .}}' 2>/dev/null",
+            f"{docker} network ls --format '{{{{json .}}}}' 2>/dev/null",
             read_timeout=60,
         )
 
@@ -1662,7 +1674,8 @@ class LinuxDriver(OSDriver):
         for img_name in candidate_images:
             try:
                 local_raw = self._send(
-                    f"docker inspect {img_name!r} --format '{{{{index .RepoDigests 0}}}}' 2>/dev/null",
+                    f"{self._docker_bin()} inspect {img_name!r} "
+                    f"--format '{{{{index .RepoDigests 0}}}}' 2>/dev/null",
                     read_timeout=5,
                 ).strip()
                 if not local_raw or "@" not in local_raw:
@@ -1670,7 +1683,7 @@ class LinuxDriver(OSDriver):
                 local_digest = local_raw.split("@", 1)[1]
 
                 remote_full = self._send(
-                    f"docker buildx imagetools inspect {img_name!r} 2>&1",
+                    f"{self._docker_bin()} buildx imagetools inspect {img_name!r} 2>&1",
                     read_timeout=30,
                 ).strip()
                 if ("429" in remote_full
@@ -1712,7 +1725,7 @@ class LinuxDriver(OSDriver):
         import shlex as _shlex
 
         raw = self._send(
-            f"docker inspect {_shlex.quote(container_id)} 2>/dev/null",
+            f"{self._docker_bin()} inspect {_shlex.quote(container_id)} 2>/dev/null",
             read_timeout=10,
         ).strip()
         if not raw:

tests/test_linux.py

@@ -802,3 +802,54 @@ class TestRunDeviceActionDispatch:
         ) as mock_action:
             driver.run_device_action("apt_update_upgrade")
         mock_action.assert_called_once()
+
+
+class TestDockerBinHook:
+    """Where the docker binary lives is device-specific; what to do with it is not.
+
+    QTS puts Container Station's docker under /share/<pool>/.qpkg/ and not on
+    PATH. Rather than duplicating the whole Docker surface in the QNAP driver,
+    the path is a one-method hook here and the logic stays generic. See
+    docs/ARCHITECTURE.md §4.4, "Generisch vs. treiberspezifisch".
+    """
+
+    def test_defaults_to_docker_on_path(self, driver):
+        assert driver._docker_bin() == "docker"
+
+    def test_detection_uses_the_hook(self, driver):
+        """A subclass pointing elsewhere must not be probed for a PATH docker."""
+        sent = []
+
+        def _record(cmd, **kwargs):
+            sent.append(cmd)
+            return ""
+
+        with patch.object(driver, "_docker_bin", return_value="/opt/cs/docker"):
+            with patch.object(driver, "_send", side_effect=_record):
+                result = driver.get_docker_info()
+
+        assert result == {"available": False}
+        assert any("/opt/cs/docker" in cmd for cmd in sent)
+        assert not any("command -v docker " in cmd for cmd in sent)
+
+    def test_all_docker_subcommands_use_the_hook(self, driver):
+        """Half-converted call sites are the failure mode here: detection would
+        find the binary and the actual queries would still miss it."""
+        sent = []
+
+        def _record(cmd, **kwargs):
+            sent.append(cmd)
+            if "command -v" in cmd:
+                return "/opt/cs/docker"
+            if "---CONTAINERS---" in cmd:
+                return "---CONTAINERS---\n---IMAGES---\n---VOLUMES---\n---NETWORKS---\n"
+            return ""
+
+        with patch.object(driver, "_docker_bin", return_value="/opt/cs/docker"):
+            with patch.object(driver, "_send", side_effect=_record):
+                driver.get_docker_info()
+
+        docker_cmds = [c for c in sent if "docker" in c]
+        assert docker_cmds
+        for cmd in docker_cmds:
+            assert "/opt/cs/docker" in cmd, f"unconverted call site: {cmd}"