fix(runtime): honor shell-selected Docker contexts

docs/advanced/configuration.mdx

@@ -175,7 +175,11 @@ When remote vars are set, Strix dual-writes telemetry to both local JSONL and th
 </ParamField>
 
 <ParamField path="DOCKER_HOST" type="string">
-  Docker daemon address, for example `unix:///var/run/docker.sock` or `tcp://10.0.0.5:2375`. When not set, Strix connects to the same daemon as the `docker` CLI: the current docker context (`docker context use`), then the default socket. Docker Desktop, OrbStack and Colima register their sockets as contexts, so no extra configuration is needed for them.
+  Docker daemon address, for example `unix:///var/run/docker.sock` or `tcp://10.0.0.5:2375`. When not set, Strix uses `DOCKER_CONTEXT`, then the saved current context (`docker context use`), then the default socket. Docker Desktop, OrbStack and Colima register their sockets as contexts, so no extra configuration is needed for them.
+</ParamField>
+
+<ParamField path="DOCKER_CONTEXT" type="string">
+  Select a Docker context for this shell without changing the saved current context. Used when `DOCKER_HOST` is unset. A missing context is an error; Strix does not silently fall back to another daemon. Set to `default` to use the SDK's default connection settings.
 </ParamField>
 
 <ParamField path="STRIX_RUNTIME_BACKEND" default="docker" type="string">

strix/runtime/docker_connection.py

@@ -44,13 +44,13 @@ def detail(self) -> str:
 
 
 def resolve_docker_endpoint(environ: dict[str, str] | None = None) -> DockerEndpoint:
-    """``DOCKER_HOST``, else the current docker context, else the SDK default."""
+    """``DOCKER_HOST``, shell/saved context, then the SDK default."""
     env = os.environ if environ is None else environ
     host = env.get("DOCKER_HOST", "").strip()
     if host:
         return DockerEndpoint(host, "DOCKER_HOST")
 
-    name = get_current_context_name()
+    name = env.get("DOCKER_CONTEXT", "").strip() or get_current_context_name()
     if name == DEFAULT_CONTEXT:
         return DockerEndpoint(None, "default socket")
 

tests/test_docker_connection.py

@@ -2,9 +2,11 @@
 
 from __future__ import annotations
 
+import hashlib
 import importlib
+import json
 from types import SimpleNamespace
-from typing import Any, cast
+from typing import TYPE_CHECKING, Any, cast
 
 import pytest
 from docker.errors import DockerException
@@ -19,6 +21,10 @@
 )
 
 
+if TYPE_CHECKING:
+    from pathlib import Path
+
+
 cli_utils: Any = importlib.import_module("strix.interface.utils")
 
 
@@ -34,7 +40,9 @@ def _sdk_error(inner: BaseException) -> DockerException:
 
 def test_docker_host_wins_over_context(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setattr(docker_connection, "get_current_context_name", lambda: "desktop-linux")
-    endpoint = resolve_docker_endpoint({"DOCKER_HOST": "tcp://10.0.0.5:2375"})
+    endpoint = resolve_docker_endpoint(
+        {"DOCKER_HOST": "tcp://10.0.0.5:2375", "DOCKER_CONTEXT": "selected"}
+    )
     assert endpoint == DockerEndpoint("tcp://10.0.0.5:2375", "DOCKER_HOST")
 
 
@@ -56,6 +64,61 @@ def test_default_context_uses_the_sdk_default(monkeypatch: pytest.MonkeyPatch) -
     assert resolve_docker_endpoint({}) == DockerEndpoint(None, "default socket")
 
 
+@pytest.mark.parametrize(
+    ("selected", "expected_host"),
+    [
+        ("selected", "unix:///tmp/strix-selected.sock"),
+        ("default", None),
+        ("", "unix:///tmp/strix-saved.sock"),
+    ],
+)
+def test_shell_context_overrides_the_saved_context(
+    monkeypatch: pytest.MonkeyPatch,
+    tmp_path: Path,
+    selected: str,
+    expected_host: str | None,
+) -> None:
+    """Read a real Docker context store, without contacting any daemon."""
+    (tmp_path / "config.json").write_text(json.dumps({"currentContext": "saved"}))
+    for name in ("saved", "selected"):
+        context_id = hashlib.sha256(name.encode()).hexdigest()
+        metadata = tmp_path / "contexts" / "meta" / context_id / "meta.json"
+        metadata.parent.mkdir(parents=True)
+        metadata.write_text(
+            json.dumps(
+                {
+                    "Name": name,
+                    "Metadata": {},
+                    "Endpoints": {
+                        "docker": {
+                            "Host": f"unix:///tmp/strix-{name}.sock",
+                            "SkipTLSVerify": True,
+                        }
+                    },
+                }
+            )
+        )
+    monkeypatch.setenv("DOCKER_CONFIG", str(tmp_path))
+    monkeypatch.setenv("DOCKER_CONTEXT", selected)
+    monkeypatch.delenv("DOCKER_HOST", raising=False)
+
+    assert resolve_docker_endpoint().host == expected_host
+
+
+def test_missing_shell_context_does_not_fall_back_to_saved_context(
+    monkeypatch: pytest.MonkeyPatch, tmp_path: Path
+) -> None:
+    (tmp_path / "config.json").write_text(json.dumps({"currentContext": "default"}))
+    monkeypatch.setenv("DOCKER_CONFIG", str(tmp_path))
+    monkeypatch.setenv("DOCKER_CONTEXT", "missing")
+    monkeypatch.delenv("DOCKER_HOST", raising=False)
+
+    with pytest.raises(
+        DockerConnectionError, match="docker context 'missing' is selected but does not exist"
+    ):
+        resolve_docker_endpoint()
+
+
 def test_missing_or_broken_current_context_is_an_error(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setattr(docker_connection, "get_current_context_name", lambda: "gone")
     monkeypatch.setattr(