--- ui.original/menu_research.lua	2025-08-18 16:40:24.000000000 +0300
+++ ui.modified/menu_research.lua	2025-11-15 21:37:59.832444800 +0200
@@ -116,7 +116,9 @@
 				if not GetWareData(temptechlist[i], "ismissiononly") then
 					-- print("found " .. temptechlist[i])
 					local state_completed = C.HasResearched(temptechlist[i])
-					table.insert(menu.techtree, { [1] = { [1] = { tech = temptechlist[i], sortorder = sortorder, completed = state_completed } } })
+					-- start fix: added empty precursor list
+					table.insert(menu.techtree,	{ [1] = { [1] = { tech = temptechlist[i], sortorder = sortorder, completed = state_completed, precursors = {} } } })
+					-- end fix: added empty precursor list
 				end
 				table.remove(temptechlist, i)
 			else
@@ -130,7 +132,9 @@
 				if hasonlymissionprecursors then
 					-- print("found with only mission precursors" .. temptechlist[i])
 					local state_completed = C.HasResearched(temptechlist[i])
-					table.insert(menu.techtree, { [1] = { [1] = { tech = temptechlist[i], sortorder = sortorder, completed = state_completed } } })
+					-- start fix: added empty precursor list
+					table.insert(menu.techtree, { [1] = { [1] = { tech = temptechlist[i], sortorder = sortorder, completed = state_completed, precursors = {} } } })
+					-- end fix: added empty precursor list
 					table.remove(temptechlist, i)
 				end
 			end
@@ -177,12 +181,26 @@

 				-- add this tech to the tree and remove it from the list
 				local state_completed = C.HasResearched(temptechlist[idx])
+				-- start fix: build new entry with precursor links
+				local newentry = { tech = temptechlist[idx], sortorder = sortorder, completed = state_completed, precursors = {} }
+				for _, precursor in ipairs(techprecursors) do
+					local precursorMainIdx, precursorCol, precursorTechIdx = menu.findTech(menu.techtree, precursor)
+					if precursorMainIdx and precursorCol and precursorTechIdx then
+						newentry.precursors[#newentry.precursors + 1] = menu.techtree[precursorMainIdx][precursorCol]
+						[precursorTechIdx]
+					end
+				end
+				-- end fix: build new entry with precursor links
 				if menu.techtree[smallestMainIdx][foundPrecusorCol + 1] then
 					-- print("    adding")
-					table.insert(menu.techtree[smallestMainIdx][foundPrecusorCol + 1], { tech = temptechlist[idx], sortorder = sortorder, completed = state_completed })
+					-- start fix: adding the data with precursor links
+					table.insert(menu.techtree[smallestMainIdx][foundPrecusorCol + 1], newentry)
+					-- end fix: adding the data with precursor links
 				else
 					-- print("    new entry")
-					menu.techtree[smallestMainIdx][foundPrecusorCol + 1] = { [1] = { tech = temptechlist[idx], sortorder = sortorder, completed = state_completed } }
+					-- start fix: replacing the data with precursor links
+					menu.techtree[smallestMainIdx][foundPrecusorCol + 1] = { [1] = newentry }
+					-- end fix: replacing the data with precursor links
 				end
 				-- print("    removed")
 				table.remove(temptechlist, idx)
@@ -365,10 +383,18 @@
 					menu.restoreNode = techentry.node
 					menu.restoreNodeTech = nil
 				end
-
-				if col > 1 then
-					for k, previousentry in ipairs(mainentry[col - 1]) do
-						-- print("adding edge from node " .. previousentry.tech .. " to " .. techentry.tech)
+				-- start fix: added predecessors handling to apply dependency fix
+				local predecessors = techentry.precursors or {}
+				if (#predecessors == 0) and (col > 1) then
+					local fallbackColumn = mainentry[col - 1]
+					if fallbackColumn then
+						predecessors = fallbackColumn
+					end
+				end
+				for k = 1, #predecessors do
+					local previousentry = predecessors[k]
+					if previousentry.node then
+						--end fix: added predecessors handling to apply dependency fix
 						local edge = previousentry.node:addEdgeTo(techentry.node)
 						if not previousentry.completed then
 							edge.properties.sourceSlotColor = Color["research_incomplete"]
@@ -913,12 +939,23 @@
 function menu.isResearchAvailable(tech, mainIdx, col)
 	if menu.availableresearchmodule then
 		if col > 1 then
-			for _, techentry in ipairs(menu.techtree[mainIdx][col - 1]) do
-				if not techentry.completed then
-					return false
+			-- start fix: finding current tech and checking its predecessors
+      		local currentColumn = menu.techtree[mainIdx][col]
+			for i = 1, #currentColumn do
+				local techentry = currentColumn[i]
+				if techentry and techentry.tech == tech then
+					if techentry.precursors and #techentry.precursors > 0 then
+						for i = 1, #techentry.precursors do
+							local precursor = techentry.precursors[i]
+							if not precursor.completed then
+								return false
+							end
+						end
+					end
 				end
 			end
+			-- end fix: finding current tech and checking its predecessors
 		end
 		return true
 	end