diff --git a/tests/test_plugin_contract_boundaries.py b/tests/test_plugin_contract_boundaries.py
new file mode 100644
index 0000000..1add5c1
--- /dev/null
+++ b/tests/test_plugin_contract_boundaries.py
@@ -0,0 +1,94 @@
+"""Offline checks of existing contracts; every configured producer stays OFF."""
+from copy import deepcopy
+import hashlib
+import json
+from pathlib import Path
+
+import pytest
+
+from quant_strategy_plugins.artifacts import sha256_file, write_json
+from quant_strategy_plugins.plugin_catalog import build_plugin_catalog
+from quant_strategy_plugins.plugin_signal_envelope_v2 import (
+    SignalEnvelopeValidationError,
+    validate_signal_envelope,
+)
+from quant_strategy_plugins.russell_1000_multi_factor_defensive_snapshot import read_table
+from quant_strategy_plugins import strategy_plugin_runner as runner
+
+
+def test_catalog_is_detached_and_has_stable_identifier_order():
+    expected = build_plugin_catalog()
+    returned = build_plugin_catalog()
+    ids = [entry["plugin_id"] for entry in expected["entries"]]
+    assert ids == sorted(ids) and len(ids) == len(set(ids))
+    returned["entries"][0]["owner_strategy"].append("synthetic_caller_mutation")
+    returned["entries"][0]["broker_order_allowed"] = True
+    assert build_plugin_catalog() == expected
+
+
+@pytest.mark.parametrize("target_type", ["strategy_plugins", "notification_targets"])
+def test_all_disabled_entries_do_not_load_inputs_or_write_signals(tmp_path, monkeypatch, target_type):
+    def unexpected_read(*args, **kwargs):
+        raise AssertionError("disabled producer must not read material")
+
+    monkeypatch.setattr(runner, "read_table", unexpected_read)
+    entries = []
+    for entry in reversed(build_plugin_catalog()["entries"]):
+        scope = {"strategy": entry["owner_strategy"][0]} if target_type == "strategy_plugins" else {
+            "notification_target": "synthetic_disabled_target",
+        }
+        entries.append({
+            **scope, "plugin": entry["plugin_id"], "enabled": False,
+            "inputs": {"prices": str(tmp_path / "must-not-exist.csv")},
+            "outputs": {"output_dir": str(tmp_path / "signals" / entry["plugin_id"])},
+        })
+    config = {"output_dir": str(tmp_path / "summary"), target_type: entries}
+    original = deepcopy(config)
+    result = runner.run_configured_plugins(config)
+    assert config == original
+    assert [r["plugin"] for r in result[target_type]] == [e["plugin"] for e in entries]
+    assert all(r["status"] == "skipped" and r["enabled"] is False
+               and r["effective_mode"] is None and r["latest_signal_path"] is None
+               for r in result[target_type])
+    assert not (tmp_path / "signals").exists()
+    assert json.loads((tmp_path / "summary/latest_run.json").read_text()) == result
+
+
+@pytest.mark.parametrize("container", ["inputs", "outputs", "settings"])
+def test_nested_settings_cannot_override_explicit_disabled_flag(container):
+    with pytest.raises(ValueError, match="duplicate strategy plugin config key.*enabled"):
+        runner._flatten_strategy_plugin_entry({
+            "plugin": "market_regime_control", "enabled": False, container: {"enabled": True},
+        })
+
+
+@pytest.mark.parametrize("plugin", ["panic_reversal_shadow", "synthetic_unknown_plugin"])
+def test_incompatible_strategy_is_rejected_without_running_a_producer(plugin):
+    with pytest.raises(ValueError, match="strategy-limited|unsupported plugin"):
+        runner._validate_plugin_strategy(plugin, "soxl_soxx_trend_income")
+
+
+def test_existing_envelope_fixture_survives_artifact_roundtrip_and_rejects_tamper(tmp_path):
+    fixture = Path(__file__).parent / "fixtures/plugin_signal_envelope_v2/valid_signal.json"
+    envelope = json.loads(fixture.read_text())
+    output = write_json(tmp_path / "frozen-synthetic-signal.json", envelope)
+    raw = output.read_bytes()
+    assert sha256_file(output) == hashlib.sha256(raw).hexdigest()
+    loaded = json.loads(raw)
+    assert validate_signal_envelope(loaded) == envelope
+    loaded["payload"]["regime"] = "synthetic_tampered_state"
+    write_json(output, loaded)
+    with pytest.raises(SignalEnvelopeValidationError, match="does not match canonical payload"):
+        validate_signal_envelope(json.loads(output.read_text()))
+
+
+def test_missing_local_material_is_rejected(tmp_path):
+    with pytest.raises(FileNotFoundError, match="file not found"):
+        read_table(tmp_path / "absent-synthetic-input.csv")
+
+
+def test_unsupported_local_material_format_is_rejected(tmp_path):
+    path = tmp_path / "synthetic-input.unsupported"
+    path.write_text("{}")
+    with pytest.raises(ValueError, match="Unsupported table format"):
+        read_table(path)