fix(direct_control): honor bare EPICS_CA_* env vars

backend/direct_control_service/src/direct_control/monitoring/pv_monitor.py

@@ -31,8 +31,12 @@
 
 # Set EPICS env vars before importing ophyd/pyepics
 # pyepics reads these at import time
+# The DIRECT_CONTROL_-prefixed forms are explicit service-level overrides only.
+# When unset, the standard EPICS_CA_* variables (and libca's own defaults,
+# e.g. AUTO_ADDR_LIST=YES) apply untouched — a deployment that sets the bare
+# variables must never have them silently overridden by a default here.
 _epics_addr = os.environ.get("DIRECT_CONTROL_EPICS_CA_ADDR_LIST")
-_epics_auto = os.environ.get("DIRECT_CONTROL_EPICS_CA_AUTO_ADDR_LIST", "YES")
+_epics_auto = os.environ.get("DIRECT_CONTROL_EPICS_CA_AUTO_ADDR_LIST")
 
 if _epics_addr:
     os.environ["EPICS_CA_ADDR_LIST"] = _epics_addr

backend/direct_control_service/tests/test_epics_env_precedence.py

@@ -0,0 +1,78 @@
+"""
+EPICS env-var precedence in the PV monitor module.
+
+pv_monitor sets EPICS_CA_* before importing ophyd/pyepics. The contract:
+the DIRECT_CONTROL_-prefixed variables are explicit overrides only — a
+deployment that sets the bare EPICS_CA_* variables (as every pod compose
+does) must see them honored, and when nothing is set at all, libca's own
+defaults apply. Regression for the silent override where an unset
+DIRECT_CONTROL_EPICS_CA_AUTO_ADDR_LIST defaulted to "YES" and clobbered
+an explicit EPICS_CA_AUTO_ADDR_LIST=NO.
+
+The logic runs at module import, so each case imports the module in a
+fresh subprocess with a controlled environment.
+"""
+
+import os
+import subprocess
+import sys
+
+_PROBE = (
+    "import os, json;"
+    "import direct_control.monitoring.pv_monitor;"
+    "print(json.dumps({"
+    "'addr': os.environ.get('EPICS_CA_ADDR_LIST'),"
+    "'auto': os.environ.get('EPICS_CA_AUTO_ADDR_LIST')}))"
+)
+
+_VARS = (
+    "EPICS_CA_ADDR_LIST",
+    "EPICS_CA_AUTO_ADDR_LIST",
+    "DIRECT_CONTROL_EPICS_CA_ADDR_LIST",
+    "DIRECT_CONTROL_EPICS_CA_AUTO_ADDR_LIST",
+)
+
+
+def _import_with(env_overrides: dict) -> dict:
+    env = {k: v for k, v in os.environ.items() if k not in _VARS}
+    env.update(env_overrides)
+    out = subprocess.run(
+        [sys.executable, "-c", _PROBE],
+        env=env,
+        capture_output=True,
+        text=True,
+        check=True,
+    )
+    import json
+
+    return json.loads(out.stdout.strip().splitlines()[-1])
+
+
+def test_bare_auto_addr_list_is_honored():
+    """An explicit EPICS_CA_AUTO_ADDR_LIST=NO survives the import untouched."""
+    result = _import_with({"EPICS_CA_AUTO_ADDR_LIST": "NO"})
+    assert result["auto"] == "NO"
+
+
+def test_bare_addr_list_is_honored():
+    result = _import_with({"EPICS_CA_ADDR_LIST": "10.0.0.1 10.0.0.2"})
+    assert result["addr"] == "10.0.0.1 10.0.0.2"
+
+
+def test_prefixed_vars_override_when_explicitly_set():
+    result = _import_with(
+        {
+            "EPICS_CA_AUTO_ADDR_LIST": "YES",
+            "DIRECT_CONTROL_EPICS_CA_AUTO_ADDR_LIST": "NO",
+            "DIRECT_CONTROL_EPICS_CA_ADDR_LIST": "192.168.1.5",
+        }
+    )
+    assert result["auto"] == "NO"
+    assert result["addr"] == "192.168.1.5"
+
+
+def test_nothing_set_leaves_libca_defaults_alone():
+    """With no EPICS config at all, the module writes nothing into the env."""
+    result = _import_with({})
+    assert result["addr"] is None
+    assert result["auto"] is None