diff --git a/drivers/tests/test_driver_contract.py b/drivers/tests/test_driver_contract.py
index 5e42ff6..d00e513 100644
--- a/drivers/tests/test_driver_contract.py
+++ b/drivers/tests/test_driver_contract.py
@@ -6,7 +6,12 @@
 
 import re
 import pytest
-from conftest import read_driver, get_driver_names, strip_lua_comments
+from conftest import (
+    read_driver,
+    read_manifest,
+    get_driver_names,
+    strip_lua_comments,
+)
 
 DRIVERS = get_driver_names()
 
@@ -72,12 +77,32 @@ def test_calls_set_make_in_init(self, driver_name):
             f"{driver_name}: should call host.set_make() in driver_init"
 
     def test_calls_emit_in_poll(self, driver_name):
-        """driver_poll should call host.emit()."""
+        """driver_poll should report each declared DER through host.emit.
+
+        `host.emit` carries a DER reading and needs a DER type the host
+        understands. Heat-pump and schema-less drivers have no matching
+        reading type, so they may report only through `host.emit_metric`.
+        Metrics remain diagnostic data for every schema-backed DER.
+        """
         if driver_name == "hello":
             pytest.skip("hello driver is a demo-only driver")
         code = read_driver(driver_name)
-        assert 'host.emit(' in code, \
-            f"{driver_name}: should call host.emit() in driver_poll"
+        if 'host.emit(' in code:
+            return
+
+        manifest = read_manifest(driver_name)
+        match = re.search(r"^ders:\s*\[([^]]*)\]\s*$", manifest, re.MULTILINE)
+        assert match, f"{driver_name}: cannot parse manifest ders"
+        ders = {
+            item.strip().strip("'\"")
+            for item in match.group(1).split(",")
+            if item.strip()
+        }
+        metric_only = not ders or ders == {"heatpump"}
+        assert metric_only and 'host.emit_metric(' in code, (
+            f"{driver_name}: declares {sorted(ders)} and must call host.emit(); "
+            f"only heat-pump or schema-less drivers may report metrics only"
+        )
 
     def test_no_forbidden_globals(self, driver_name):
         """Driver must not use forbidden sandbox-escaping functions."""
diff --git a/drivers/tests/test_mqtt_drivers.py b/drivers/tests/test_mqtt_drivers.py
index c9e78e0..59cd45d 100644
--- a/drivers/tests/test_mqtt_drivers.py
+++ b/drivers/tests/test_mqtt_drivers.py
@@ -14,6 +14,51 @@
 
 MQTT_DRIVERS = get_mqtt_drivers()
 
+_TOPIC_PART = r'(?:(?:"(?:\\.|[^"\\])*")|(?:[A-Za-z_]\w*))'
+_TOPIC_EXPRESSION = re.compile(
+    rf'{_TOPIC_PART}(?:\s*\.\.\s*{_TOPIC_PART})*'
+)
+
+
+def _file_local_names(code):
+    """Return names declared before the first function in a Lua file."""
+    first_function = re.search(
+        r'^\s*(?:local\s+)?function\b',
+        code,
+        re.MULTILINE,
+    )
+    preamble = code[:first_function.start()] if first_function else code
+    return set(re.findall(
+        r'^\s*local\s+([A-Za-z_]\w*)\s*=',
+        preamble,
+        re.MULTILINE,
+    ))
+
+
+def _is_static_topic_expression(arg, file_local_names):
+    """Accept literals and concatenations of declared file-local names."""
+    if not _TOPIC_EXPRESSION.fullmatch(arg):
+        return False
+    without_strings = re.sub(r'"(?:\\.|[^"\\])*"', '', arg)
+    names = set(re.findall(r'\b[A-Za-z_]\w*\b', without_strings))
+    return names <= file_local_names
+
+
+@pytest.mark.parametrize(
+    ("arg", "file_local_names", "expected"),
+    [
+        ('"fixed/#"', set(), True),
+        ('BASE_TOPIC .. "/#"', {"BASE_TOPIC"}, True),
+        ('topic', set(), False),
+        ('BASE_TOPIC .. topic', {"BASE_TOPIC"}, False),
+        ('msg.topic', set(), False),
+        ('make_topic()', {"make_topic"}, False),
+    ],
+)
+def test_static_topic_expression_requires_file_local_names(
+        arg, file_local_names, expected):
+    assert _is_static_topic_expression(arg, file_local_names) is expected
+
 
 @pytest.mark.parametrize("driver_name", MQTT_DRIVERS)
 class TestMqttSubscription:
@@ -37,22 +82,33 @@ def test_subscribes_in_driver_init(self, driver_name):
             f"not elsewhere"
         )
 
-    def test_subscription_topics_are_strings(self, driver_name):
-        """All mqtt_subscribe calls should use string literal topics."""
+    def test_subscription_topics_are_static(self, driver_name):
+        """A subscription topic must be decidable without running the driver.
+
+        A literal is the common case. A file-local constant or configurable
+        prefix is the other one. Function-local names do not qualify because
+        they can come from a received message.
+
+        What this rejects is a topic taken from runtime data: an index, a
+        field or a call, which is how a driver ends up subscribing to whatever
+        a message told it to.
+        """
         code = read_driver(driver_name)
         clean = strip_lua_comments(code)
+        file_names = _file_local_names(clean)
 
-        # Find all subscribe calls and verify they use string literals
         sub_calls = re.findall(
             r'host\.mqtt_subscribe\s*\(\s*(.+?)\s*\)',
             clean,
         )
 
         for call_arg in sub_calls:
-            # Should be a string literal (starts with ")
-            assert call_arg.strip().startswith('"'), (
-                f"{driver_name}: mqtt_subscribe should use string literal "
-                f"topic, found: {call_arg}"
+            arg = call_arg.strip()
+            static = _is_static_topic_expression(arg, file_names)
+            assert static, (
+                f"{driver_name}: mqtt_subscribe topic must be a literal or a "
+                f"concatenation of literals and declared file-local names, "
+                f"found: {arg}"
             )