fix(market-intel): mount mcp compose for preflight

tests/test_market_intel_skeleton.py

@@ -674,6 +674,12 @@ def test_mcp_deploy_preflight_blocks_without_required_env():
     assert preflight["would_write_database"] is False
 
 
+def test_mcp_compose_is_mounted_read_only_for_preflight():
+    compose = Path("docker-compose.yml").read_text(encoding="utf-8")
+
+    assert "./docker-compose.mcp.yml:/app/docker-compose.mcp.yml:ro" in compose
+
+
 def test_mcp_deploy_preflight_ready_when_env_contract_is_present():
     preflight = build_mcp_deploy_preflight_plan(
         env={