R-325 (felhom.eu half): hub_copy_gate accepts the controller gate importing the shared stem list

Once retrieval_promise_gate.py imports customer_copy_vocab and drops its STEMS literal, the drift
check reads "ok — single source" instead of failing on the missing literal. An import only in a
comment, or beside a stale literal, is still drift. Pinned by scripts/test_hub_copy_drift.py.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

scripts/hub_copy_gate.py

@@ -189,18 +189,31 @@ def scan_stems():
     return convictions, seen
 
 
-def check_drift():
+# R-325: the destination — the controller gate IMPORTS the shared list instead of carrying a literal.
+# Matched at the start of a line, so an import written only in a `#` comment does not count.
+_SHARED_IMPORT_RE = re.compile(
+    r"^(?:from\s+customer_copy_vocab\s+import\s+[^\n]*\bRETRIEVAL_STEMS\b|import\s+customer_copy_vocab\b)", re.M)
+
+
+def check_drift(sibling=None):
     """The controller gate's STEMS must equal the shared list. Returns (status, message).
 
     status: "ok" | "drift" | "inconclusive"
+
+    R-325: once the controller gate imports `customer_copy_vocab` and carries NO `STEMS` literal of its
+    own, the two cannot diverge and that is "ok". A literal, if present, is still compared — an import
+    beside a stale literal is drift. Pinned by scripts/test_hub_copy_drift.py.
     """
-    sibling = os.path.join(os.path.dirname(_REPO), "felhom-controller",
-                           "controller", "scripts", "retrieval_promise_gate.py")
+    if sibling is None:
+        sibling = os.path.join(os.path.dirname(_REPO), "felhom-controller",
+                               "controller", "scripts", "retrieval_promise_gate.py")
     if not os.path.exists(sibling):
         return "inconclusive", ("the felhom-controller clone is absent, so the shared stem list "
                                "could not be compared against the gate that also uses it (%s)" % sibling)
     text = open(sibling, encoding="utf-8").read()
     m = re.search(r"^STEMS\s*=\s*\[(.*?)\]", text, re.M | re.S)
+    if not m and _SHARED_IMPORT_RE.search(text):
+        return "ok", "controller gate imports the shared list (customer_copy_vocab.py) — single source"
     if not m:
         return "drift", "could not find a STEMS list in the controller gate — its shape changed"
     theirs = re.findall(r"[\"']([^\"']+)[\"']", m.group(1))