-- Original loaded-only succession. No ABMs, map emergence, timers or world registry.
return function(hearth, api)
	local S = {BUDGET = 8, RADIUS = 12, INTERVAL = 1, MAX_GAP = 1200, CACHE_LIMIT = 8192,
		MAX_TREE_CELLS=810, MAX_WATER_DEPTH=6}
	local PREFIX, PERIOD = "hearth:", 60
	local kinds = {meadow_grass=true, wildflowers=true, fern=true, litter=true, fungi=true,
		deadwood=true, young_tree=true, mature_tree=true, tree_seedling=true, dung=true,
		spring_greens_patch=true, autumn_mushrooms_patch=true}
	local trees = {tree_seedling=true, young_tree=true, mature_tree=true}
	local diversity = hearth.diversity
	local botany = hearth.botany
	local effects = hearth.species_effects
	-- Content may inject the factory before succession. Standalone integrations
	-- without it keep their old API; the engine loads only this fixed sibling.
	if botany and not effects and api.get_modpath then
		effects=dofile(api.get_modpath("hearth").."/species_effects.lua")(hearth,api)
		hearth.species_effects=effects
	end
	if botany then
		for _,r in ipairs(botany.list()) do
			if r.group~="trees" then kinds[r.id]=true end
		end
	end
	if diversity then
		for _,k in ipairs(diversity.plants) do kinds[k]=true end
		for _,species in ipairs(diversity.species_order) do
			for _,stage in ipairs({"seedling","young","mature"}) do
				local k=species.."_"..stage; kinds[k]=true; trees[k]=true
			end
		end
	end
	local offsets = {{1,0}, {0,1}, {-1,0}, {0,-1}, {2,1}, {-2,-1}, {1,-2}, {-1,2}}
	local seen, ring, ring_index, cursor, player_index, elapsed = {}, {}, 1, 0, 0, 0
	local function key(p) return p.x .. ":" .. p.y .. ":" .. p.z end
	local function at(p, x, y, z) return {x=p.x+x, y=p.y+y, z=p.z+z} end
	local function position(p)
		if type(p) ~= "table" then return nil end
		for _, axis in ipairs({"x", "y", "z"}) do
			local n = p[axis]
			if type(n) ~= "number" or n ~= n or math.abs(n) > 30990 then return nil end
		end
		return {x=math.floor(p.x+0.5), y=math.floor(p.y+0.5), z=math.floor(p.z+0.5)}
	end
	local function node(p)
		local n = api.get_node_or_nil(p)
		if n and n.name ~= "ignore" then return n end
	end
	local function kind(n)
		local name=type(n)=="table" and n.name or n
		if type(name)~="string" then return nil end
		return hearth.seasons and hearth.seasons.kind(name) or name:match("^hearth:(.+)$")
	end
	local function family(k) return diversity and diversity.family(k) or k end
	local function number(meta, field, maximum)
		local n = tonumber(meta:get_string(field))
		if not n or n ~= n or n < 0 or n == math.huge then return 0 end
		return math.min(maximum or 1000000000000, n)
	end
	local markers = {"owner", "planter", "placed_by", "player_placed", "hearth_placed", "hearth_player_placed", "planted_at"}
	local function marked(p)
		local meta = api.get_meta(p)
		-- Unknown third-party placement/provenance metadata is not ours to erase.
		-- Keep the named fallback for minimal API mocks and older integrations.
		if meta.to_table then
			local value = meta:to_table()
			for field, text in pairs(value and value.fields or {}) do
				local harvest=botany and field=="botany_ready_at" and tonumber(text)
					and tonumber(text)>=0 and tonumber(text)<math.huge
				if field:sub(1,5) ~= "succ_" and not harvest and text ~= "" and tostring(text) ~= "0" then return true end
			end
		end
		for _, field in ipairs(markers) do
			local value = meta:get_string(field)
			if value ~= "" and value ~= "0" then return true end
		end
		return false
	end
	local function permitted(p)
		-- Autonomous nature has no claim-owner identity, including on shared claims.
		if hearth.claim_owner_at then
			local owner, ambiguous = hearth.claim_owner_at(p)
			if owner or ambiguous then return false end
		end
		-- Player access deliberately rejects empty names, even on unclaimed ground.
		-- Nature must instead explicitly exclude claims and external protection.
		local protection = hearth.external_protected or api.is_protected
		return not (protection and protection(p, "")) and not marked(p)
	end
	local function ground(p)
		local n = node(p)
		return n and (n.name == PREFIX.."grass" or n.name == PREFIX.."soil"
			or (diversity and (diversity.is_ground(n) or diversity.is_rock(n))))
	end
	local function natural(p, n)
		return n and (kinds[kind(n)] or (botany and api.get_meta(p):get_string("succ_component")~=""))
			and api.get_meta(p):get_string("succ_natural") == "1"
	end
	-- Semantic substrate observations never replace water, logs or terrain.
	-- A water stand occupies AIR above a separately conserved source column.
	local function substrate(p)
		local below=at(p,0,-1,0)
		local n=node(below)
		if not n then return nil end
		local k=kind(n)
		if ground(below) then return {ground=k,substrate=k,water=0,base=below} end
		if not botany then return nil end
		if k=="water_source" then
			for depth=1,S.MAX_WATER_DEPTH do
				local q=at(p,0,-depth,0)
				local w=node(q)
				if not w or kind(w)~="water_source" or not permitted(q) then return nil end
				local bottom=at(p,0,-depth-1,0)
				local b=node(bottom)
				if not b or not permitted(bottom) then return nil end
				if kind(b)~="water_source" then
					if not ground(bottom) and kind(b)~="sand" then return nil end
					return {ground=kind(b),substrate="water",water=depth,base=bottom,freshwater=true}
				end
			end
		elseif natural(below,n) and permitted(below) then
			if k=="deadwood" or k=="litter" then
				return {ground=k,substrate=k,water=0,base=below,host=api.get_meta(below):get_string("succ_species")}
			elseif family(k)=="log" or family(k)=="young_tree" or family(k)=="mature_tree" then
				local id=botany.kind(n) or api.get_meta(below):get_string("succ_species")
				return {ground="bark",substrate="bark",water=0,base=below,host=id}
			end
		end
	end
	local function site(p)
		local n, below = node(p), at(p,0,-1,0)
		if not n or not substrate(p) or not permitted(p) or not permitted(below) then return false end
		if n.name ~= "air" and not natural(p, n) then return false end
		if not botany and diversity and n.name~="air" and not diversity.supports_ground(kind(n),node(below)) then return false end
		-- A conservative buffer around farms/builds/markers; unknown/unloaded fails closed.
		for x=-1,1 do for z=-1,1 do for y=0,2 do
			local q = at(p,x,y,z)
			local other = node(q)
			if not other or marked(q) then return false end
			local name = family(kind(other))
			if other.name ~= "air" and not natural(q, other)
				and name ~= "leaves" and name ~= "log"
				and not (botany and kind(other)=="water_source" and permitted(q))
				and not (diversity and diversity.is_worldgen_flora(other) and permitted(q)) then return false end
		end end end
		return true
	end
	function S.habitat(raw)
		local p = position(raw)
		local h = {grass=0, flowers=0, cover=0, water=0, canopy=0, loaded=true, moisture=0, light=0,
			edible=0,pollination=0,species_counts={}}
		if not p then h.loaded=false; return h end
		local support=node(at(p,0,-1,0))
		h.ground=kind(support)
		local sub=substrate(p)
		if botany and not sub then h.loaded=false; return h end
		if botany then
			h.ground,h.substrate,h.water,h.host=sub.ground,sub.substrate,sub.water,sub.host
			h.freshwater=sub.freshwater==true
			h.aquatic="land"; h.near_water=0; h.nursery=0; h.root_fungi={}
			-- Support-class pH is a deliberately coarse game observation.
			h.ph=({peat=4.5,podzol=5,alpine_turf=5.5,granite=5,basalt=6.5,
				limestone=7.5,slate=5.5,sandstone=5.5,scree=5.5,stone=5.5,
				forest_floor=5.5,alluvium=6.5,grass=6.5,soil=6.5,sand=6.5,bark=5.5,deadwood=5.5,litter=5.5})[h.ground]
		end
		h.nutrients=number(api.get_meta(at(p,0,-1,0)),"succ_nutrients",8)
		-- Leafless deciduous branches cast less shade than a summer canopy.
		local season=hearth.seasons and hearth.seasons.season() or "Summer"
		local foliage = season == "Winter" and 0.15 or 1
		-- Fixed 5x5x5 stencil: includes river water, vegetation and overhead canopy.
		for x=-2,2 do for z=-2,2 do for y=-1,3 do
			local q = at(p,x,y,z)
			local n = node(q)
			if not n then h.loaded=false
			else
				local k = kind(n)
				local f=family(k)
				local evergreen=k=="pine_leaves" or k=="spruce_leaves"
					or (diversity and (diversity.tree_info(k)=="pine" or diversity.tree_info(k)=="spruce"))
				local shade=evergreen and 1 or foliage
				if k == "water_source" or k == "water_flowing" then
					if botany then h.near_water=h.near_water+1 else h.water=h.water+1 end
				end
				-- A tree's own crown shades its neighbours, not its root's
				-- establishment test. Otherwise every grown tree self-starves.
				if f == "leaves" and not (botany and api.get_meta(q):get_string("succ_component")==key(p)) then h.canopy=h.canopy+0.15*shade end
				if natural(q,n) then
					local owner_root=api.get_meta(q):get_string("succ_component")
					local component=owner_root~="" and owner_root~=key(q)
					if botany and permitted(q) then
						local r=botany.get(botany.kind(n))
						if r then
							-- One rooted mat, not every tree component or stacked sprite.
							-- Use the existing stencil; never a new radius scan.
							if y==0 and not component and botany.active(r.id,season) then
								local below=at(q,0,-1,0)
								local b=node(below)
								local supported=(r.id=="sphagnum" and b and (kind(b)=="peat" or kind(b)=="alluvium"))
									or (r.id=="duckweed" and b and kind(b)=="water_source")
									or (r.id=="alder" and trees[k] and ground(below))
								if supported and permitted(below) then
									h.species_counts[r.id]=(h.species_counts[r.id] or 0)+1
								end
							end
							if not h.host and r.group=="trees" then h.host=r.id end
							if r.group=="grasses" then h.grass=h.grass+1 end
							if botany.pollinator(k,season) and r.group~="trees" then h.flowers=h.flowers+1 end
							if r.group=="shrubs" or r.group=="ferns_mosses" or r.group=="aquatic" then h.cover=h.cover+1 end
							if botany.browse(k,season) and not component then h.edible=h.edible+1 end
							if botany.pollinator(k,season) and not component then h.pollination=h.pollination+1 end
							if botany.active(k,season) and r.tags.nursery and not component then h.nursery=h.nursery+1 end
							if r.group=="fungi" and r.tags.ectomycorrhiza and botany.active(k,season) then h.root_fungi[#h.root_fungi+1]=r.id end
						end
					end
					if k == "meadow_grass" then h.grass=h.grass+1 end
					if k == "wildflowers" then h.flowers=h.flowers+1 end
					if k == "fern" or trees[k] or (diversity and diversity.is_worldgen_flora(k)) then h.cover=h.cover+1 end
					if f == "mature_tree" and api.get_meta(q):get_string("succ_tree_stage")=="" then h.canopy=h.canopy+shade end
					if f == "young_tree" and api.get_meta(q):get_string("succ_tree_stage")=="" then h.canopy=h.canopy+0.5*shade end
					if diversity and not botany and diversity.edible(k) then h.edible=h.edible+1 end
					if diversity and (not botany or not botany.kind(k)) and diversity.pollinator(k,season) then h.pollination=h.pollination+1 end
				end
			end
		end end end
		local light = api.get_node_light and api.get_node_light(p, 0.5)
		h.light = math.max(0, math.min(15, light or 15) - h.canopy*3)
		local biome = api.get_biome_data and api.get_biome_data(p)
		h.heat=biome and biome.heat or 50
		h.moisture = math.min(1, (biome and biome.humidity or 45)/100 + math.min(0.5,(h.near_water or h.water)*0.1) + h.canopy*0.08)
		local surfaces=hearth.biomes and hearth.biomes.surface
		local surface=surfaces and surfaces(support)
		local soil_moisture=surface and surface.moisture
			or ({forest_floor=0.6,podzol=0.4,alluvium=0.85,peat=1,alpine_turf=0.35})[h.ground]
		if soil_moisture then h.moisture=math.min(1,(h.moisture+soil_moisture)/2) end
		if botany then
			if h.water>0 then
				local r=botany.get(node(p))
				h.aquatic=r and r.niche.aquatic or ((math.abs(p.x*17+p.z*31)%2==0) and "surface" or "submerged")
				h.moisture=1
			elseif h.near_water>0 and h.moisture>=0.65 then h.aquatic="bank" end
		end
		return effects and effects.habitat(h,h.species_counts) or h
	end
	local function active(p, now)
		local k = key(p)
		local previous = seen[k]
		if not previous then
			local evicted = ring[ring_index]
			if evicted then seen[evicted]=nil end
			ring[ring_index]=k; ring_index=ring_index%S.CACHE_LIMIT+1
		end
		seen[k]=now
		-- Restart, cache eviction, clock rewind and long absences only rebaseline.
		if not previous or now <= previous or now-previous > S.MAX_GAP then return 0 end
		return now-previous
	end
	local function tree_clear(p)
		-- Species mature geometry reaches five nodes/±1.5. Conservative
		-- 5x5x6 target volume, checked loaded/protected/marked, never emerged.
		for x=-2,2 do for z=-2,2 do for y=0,5 do
			local q = at(p,x,y,z)
			local n = node(q)
			if not n or not permitted(q) then return false end
			if not (x==0 and y==0 and z==0) and n.name ~= "air" then
				if not natural(q,n) or trees[kind(n)] then return false end
			end
		end end end
		return true
	end
	local tree_epoch
	local function plan_for(species,stage)
		local plan=diversity and diversity.tree_plan and diversity.tree_plan(species,stage)
		if type(plan)~="table" or #plan==0 or #plan>S.MAX_TREE_CELLS then return nil end
		local root,seen_cells=false,{}
		for _,c in ipairs(plan) do
			if type(c)~="table" then return nil end
			for _,axis in ipairs({"x","y","z"}) do
				local v=c[axis]
				if type(v)~="number" or v~=v or v%1~=0 or math.abs(v)>(axis=="y" and 9 or 4) or (axis=="y" and v<0) then return nil end
			end
			local k=kind(c.name)
			local f=family(k)
			if f~="log" and f~="leaves" and f~="young_tree" and f~="mature_tree" then return nil end
			local rootkind=species=="generic" and (stage=="young" and "young_tree" or "mature_tree") or species.."_"..stage
			local wood=species=="generic" and "log" or species.."_log"
			local leaves=species=="generic" and "leaves" or species.."_leaves"
			if k~=rootkind and k~=wood and k~=leaves then return nil end
			local rotation=c.param2 or 0
			if type(rotation)~="number" or rotation~=rotation or rotation%1~=0 or rotation<0 or rotation>23 then return nil end
			if c.name:sub(1,7)~=PREFIX or seen_cells[key(c)] then return nil end
			seen_cells[key(c)]=true
			if c.x==0 and c.y==0 and c.z==0 then root=true end
		end
		return root and plan or nil
	end
	local function owned(p,root,expected)
		local n=node(p)
		local m=api.get_meta(p)
		return n and natural(p,n) and m:get_string("succ_component")==root
			and kind(n)==kind(expected.name) and (n.param2 or 0)==(expected.param2 or 0)
	end
	local function components(p,species,stage)
		local plan=plan_for(species,stage)
		if not plan then return nil end
		local cells={}
		for _,c in ipairs(plan) do cells[key(at(p,c.x,c.y,c.z))]=c end
		return cells,plan
	end
	local function clear_component(q)
		api.swap_node(q,{name="air"})
		local m=api.get_meta(q)
		for _,f in ipairs({"succ_natural","succ_component","succ_species","succ_age","succ_stress"}) do m:set_string(f,"") end
	end
	local function tree_transition(p,target,removed)
		-- Reserve before generating even the read-only geometry, so eight
		-- competing roots cannot each construct a full plan in one second.
		local epoch=os.time()
		if tree_epoch==epoch then return false end
		tree_epoch=epoch
		local m=api.get_meta(p)
		local current=removed or kind(node(p))
		local species,stage=diversity.tree_info(current)
		species=species or "generic"
		stage=stage or ({young_tree="young",mature_tree="mature"})[current]
		local _,next_stage=diversity.tree_info(target)
		next_stage=next_stage or ({young_tree="young",mature_tree="mature"})[target]
		local previous=m:get_string("succ_tree_stage")
		if removed then previous=stage end
		if previous=="" then previous=nil end
		local old,oldplan={},{}
		if previous then
			old,oldplan=components(p,species,previous)
			if not old then return false end
		end
		local plan={}
		if next_stage then plan=plan_for(species,next_stage); if not plan then return false end end
		local root=key(p)
		local destinations,extras={},{}
		for _,c in ipairs(oldplan) do destinations[key(at(p,c.x,c.y,c.z))]={c=c,old=true} end
		for _,c in ipairs(plan) do
			local id=key(at(p,c.x,c.y,c.z))
			destinations[id]=destinations[id] or {}; destinations[id].next=c
		end
		-- One full plan preflight/application per wall-clock second globally,
		-- including failed attempts. Never multiply tree work by player count.
		for id,cell in pairs(destinations) do
			local c=cell.c or cell.next
			local q=at(p,c.x,c.y,c.z)
			local n=node(q)
			local support=at(q,0,-1,0)
			if not position(q) or not n or not node(support) or not permitted(q) or not permitted(support) then return false end
			if id~=root then
				if cell.old then
					if n.name~="air" and not owned(q,root,old[id]) then return false end
				elseif n.name~="air" then return false end
			elseif removed then
				if n.name~="air" then return false end
			elseif not natural(q,n) then return false end
			-- Epiphytes are not tree components. Refuse growth into them; on
			-- death remove only explicitly natural occupants losing their wood.
			if not next_stage and cell.old and family(kind(c.name))=="log" then
				local above=at(q,0,1,0)
				local a=node(above)
				if not a or not permitted(above) then return false end
				if a.name~="air" and not destinations[key(above)] and not (botany and botany.kind(a) and natural(above,a)) then return false end
				if botany and botany.kind(a) and natural(above,a) and not destinations[key(above)] then extras[key(above)]=above end
			end
		end
		-- All destinations passed before the first write. Lua callbacks execute
		-- synchronously; no yielding, inventory callbacks or map emergence here.
		for _,q in pairs(extras) do clear_component(q) end
		for id,cell in pairs(destinations) do
			local c=cell.c or cell.next
			local q=at(p,c.x,c.y,c.z)
			if id~=root then
				if cell.next then
					local nextcell=cell.next
					local name=hearth.seasons and hearth.seasons.name_for(kind(nextcell.name)) or nextcell.name
					api.swap_node(q,{name=name,param2=nextcell.param2 or 0})
					local cm=api.get_meta(q)
					cm:set_string("succ_natural","1"); cm:set_string("succ_component",root)
					cm:set_string("succ_species",species)
				elseif node(q).name~="air" then clear_component(q) end
			end
		end
		m:set_string("succ_tree_stage",next_stage or "")
		if removed then
			m:set_string("succ_component",""); m:set_string("succ_natural","")
			if hearth.invalidate_environment then hearth.invalidate_environment(p) end
			return true
		end
		m:set_string("succ_component",next_stage and root or "")
		return true
	end
	local function change(p, target)
		-- All callers preflight; recheck source and natural support immediately before writing.
		if not site(p) then return false end
		local h=botany and S.habitat(p)
		if botany then
			if not h.loaded then return false end
			if target and botany.kind(target) then
				if not botany.suitable(target,h,hearth.seasons and hearth.seasons.season() or "Summer") then return false end
			elseif target and (h.water>0 or h.substrate=="bark" or h.substrate=="deadwood" or h.substrate=="litter") then return false end
		elseif diversity and target and not diversity.supports_ground(target,node(at(p,0,-1,0))) then return false end
		local expanding=family(target)=="young_tree" or family(target)=="mature_tree"
		local managed=api.get_meta(p):get_string("succ_tree_stage")~=""
		if diversity and (expanding or managed) and (botany or managed or hearth.biomes) then
			if not tree_transition(p,target) then return false end
		elseif expanding and not tree_clear(p) then return false end
		-- A wood/litter substrate can carry one natural fungus/epiphyte above
		-- it. Do not leave that occupant hanging when its substrate is spent.
		if botany and (kind(node(p))=="deadwood" or kind(node(p))=="litter") then
			local above=at(p,0,1,0)
			local a=node(above)
			if not a or not permitted(above) then return false end
			if a.name~="air" then
				if not natural(above,a) or not botany.kind(a) then return false end
				clear_component(above)
			end
		end
		local origin=diversity and diversity.tree_info(kind(node(p)))
		local name = target and (hearth.seasons and hearth.seasons.name_for(target) or PREFIX..target) or "air"
		api.swap_node(p, {name=name,param2=target=="deadwood" and 12 or 0})
		local m = api.get_meta(p)
		local species=diversity and diversity.tree_info(target)
		if species or origin then m:set_string("succ_species",species or origin)
		elseif target~="deadwood" and target~="litter" then m:set_string("succ_species","") end
		m:set_string("succ_natural", target and "1" or "")
		m:set_string("succ_age", "0"); m:set_string("succ_stress", "0")
		if hearth.invalidate_environment then hearth.invalidate_environment(p) end
		return true
	end
	-- Optional after-dig handoff. Root identity comes from the old node, never
	-- executable serialized metadata. Only this root's matching components go.
	function S.tree_removed(raw,oldnode)
		local p=position(raw)
		if not p or not diversity or not oldnode then return false end
		local k=kind(oldnode)
		local f=family(k)
		if f~="young_tree" and f~="mature_tree" then return false end
		if not node(p) or node(p).name~="air" or not permitted(p) or not permitted(at(p,0,-1,0)) then return false end
		return tree_transition(p,nil,k)
	end
	if api.register_on_dignode then api.register_on_dignode(function(p,oldnode) S.tree_removed(p,oldnode) end) end
	local function nutrients(p, amount)
		local below = at(p,0,-1,0)
		if not ground(below) or not permitted(below) then return end
		if diversity and not diversity.is_ground(node(below)) then return end
		local m = api.get_meta(below)
		m:set_string("succ_nutrients", tostring(math.max(0,math.min(8,number(m,"succ_nutrients",8)+amount))))
		return true
	end
	local function disperse(p, target, serial)
		local d = offsets[serial%#offsets+1]
		local q = at(p,d[1],0,d[2])
		if not site(p) or not site(q) or node(q).name ~= "air" then return false end
		local dest = S.habitat(q)
		if not dest.loaded then return false end
		if botany and botany.kind(target) then
			if not botany.suitable(target,dest,hearth.seasons and hearth.seasons.season() or "Summer") then return false end
		elseif diversity and not diversity.suitable(target,dest) then return false end
		if family(target) == "tree_seedling" and (dest.canopy >= 1.5 or dest.grass+dest.flowers >= 15) then return false end
		if target == "meadow_grass" and (dest.light < 9 or dest.moisture>=0.75) then return false end
		if target == "wildflowers" and (dest.light < 11 or dest.grass >= 10) then return false end
		if target == "fern" and (dest.light > 12 or dest.moisture < 0.55) then return false end
		if target == "spring_greens_patch" and (dest.light < 9 or dest.moisture < 0.55) then return false end
		if target == "autumn_mushrooms_patch" and (dest.light > 10 or dest.moisture < 0.6) then return false end
		if hearth.seasons and not hearth.seasons.available(target) then return false end
		local m = api.get_meta(q)
		-- Destination cooldown survives grazing, decay and restart; no repeated seed rerolls.
		local now = os.time()
		if number(m,"succ_next") > now then return false end
		if not change(q,target) then return false end
		m:set_string("succ_next", tostring(now+PERIOD))
		nutrients(q,-1)
		return true
	end
	local function observe(p, now)
		if not site(p) then seen[key(p)]=nil; return false end
		local component=api.get_meta(p):get_string("succ_component")
		if component~="" and component~=key(p) then return false end
		local dt = active(p,now)
		local m, n = api.get_meta(p), node(p)
		if dt == 0 then return false end
		local h = S.habitat(p)
		if not h.loaded then seen[key(p)]=nil; return false end
		local k = kind(n)
		local f=family(k)
		local species=diversity and diversity.tree_info(k)
		local record=botany and botany.get(k)
		local season=hearth.seasons and hearth.seasons.season(now) or "Summer"
		local climate = hearth.climate_at and hearth.climate_at(now)
		local warm = not climate or (climate.temperature or 12) >= 3
		local decomposer = k=="dung" or k=="litter" or k=="deadwood" or k=="fungi"
		local dormant = (record and not botany.active(k,season)) or (hearth.seasons and not hearth.seasons.available(k,now))
		local age_dt = (not decomposer and (not warm or dormant)) and 0 or dt
		local age = number(m,"succ_age",1000000)+age_dt
		m:set_string("succ_age", tostring(age))
		if number(m,"succ_next") > now then return false end
		-- Commit the attempt BEFORE evaluating it, including failed competition/dispersal.
		m:set_string("succ_next", tostring(now+PERIOD))
		local serial = number(m,"succ_serial",1000000000)+1
		m:set_string("succ_serial", tostring(serial))
		local fertility = number(api.get_meta(at(p,0,-1,0)),"succ_nutrients",8)
		if n.name == "air" then
			if warm and (botany or not hearth.seasons or hearth.seasons.season(now)~="Winter")
				and age >= (fertility>0 and 90 or 180) and h.light >= (botany and 2 or 5) then
				local target = h.light<10 and h.moisture>=0.55 and "fern" or "meadow_grass"
				if h.light>=11 and h.grass>=2 and h.grass<10 and (p.x+p.z)%4==0 then target="wildflowers" end
				if hearth.seasons then
					if hearth.seasons.season(now)=="Autumn" and target=="wildflowers" then target="meadow_grass" end
					if hearth.seasons.available("spring_greens_patch",now) and h.light>=9 and h.moisture>=0.55
						and (p.x*3+p.z*5)%7==0 then target="spring_greens_patch" end
					if hearth.seasons.available("autumn_mushrooms_patch",now) and h.light<=10 and h.moisture>=0.6
						and (p.x+p.z)%5==0 then target="autumn_mushrooms_patch" end
				end
				if botany then
					-- No optimistic meadow fallback for bark, saturated banks,
					-- water or a missing botanical niche. Use the actual returned
					-- node kind, never the descriptor ID (trees have stage IDs).
					h.include_trees=age>=7200 and h.canopy<1.5 and (p.x*7+p.z*11)%23==0
					target=botany.choose(p,h,season)
					if not target then return false end
				elseif diversity then
					target=diversity.choose_recruit(p,h,hearth.seasons and hearth.seasons.season(now) or "Summer") or target
					-- Saturated riparian soils cannot silently fall back to meadow;
					-- exposed bedrock admits lichen only, never soil replacement.
					if not diversity.supports_ground(target,node(at(p,0,-1,0)))
						or (target=="meadow_grass" and h.moisture>=0.75) then return false end
				end
				if h.light<9 and target=="meadow_grass" then return false end
				if change(p,target) then nutrients(p,-1); return true end
			end
			return false
		end
		-- Perennials rest rather than die at first frost. Autumn litter keeps
		-- entering the nutrient cycle in winter; decomposition remains active.
		if not decomposer and (not warm or dormant) then
			if f=="mature_tree" and serial%5==0 then disperse(p,"litter",serial) end
			return false
		end
		local harsh = (k=="meadow_grass" and h.light<8) or (k=="wildflowers" and (h.light<10 or h.grass>=12))
			or (k=="fern" and (h.moisture<0.5 or h.light>13)) or (trees[k] and (h.moisture<0.25 or h.light<4))
		if record then
			if not botany.suitable(k,h,season) then harsh=true end
		elseif diversity and diversity.is_worldgen_flora(k) and not diversity.suitable(k,h) then harsh=true end
		local stress_dt=botany and h.nursery>0 and dt*0.75 or dt
		local stress = harsh and number(m,"succ_stress",100000)+stress_dt or 0
		m:set_string("succ_stress",tostring(stress))
		if stress>=600 then
			local remains=trees[k] and "deadwood" or "litter"
			if botany and ((record and record.group=="fungi") or h.water>0 or h.substrate=="bark" or h.substrate=="deadwood" or h.substrate=="litter") then remains=nil end
			if diversity and diversity.is_rock(node(at(p,0,-1,0))) then remains=nil end
			return change(p,remains)
		end
		if decomposer then
			local lifetime = ({dung=600,litter=1800,deadwood=7200,fungi=2400})[k]
			if age>=lifetime then
				local target = k=="deadwood" and "litter" or nil
				if change(p,target) then nutrients(p,k=="dung" and 4 or (k=="deadwood" and 3 or 1)); return true end
			elseif k~="fungi" and h.moisture>=0.55 and h.light<=12 and age>=300 then
				disperse(p,"fungi",serial)
			end
			return false
		end
		if not warm then return false end
		if record and age>=900 and record.tags.nitrogenfixer then
			local below=at(p,0,-1,0)
			local soil=api.get_meta(below)
			local fixed=number(soil,"succ_fixed_nitrogen",2)
			local delta=math.min(botany.nitrogen(k,fixed),math.max(0,4-fertility))
			if delta>0 and fertility<4 and permitted(p) and permitted(below) and nutrients(p,delta) then
				soil:set_string("succ_fixed_nitrogen",tostring(fixed+delta))
			end
		end
		local seed_age=21600
		local exchange=0
		if botany and species and f=="tree_seedling" then
			for _,fungus in ipairs(h.root_fungi) do exchange=math.max(exchange,botany.root_fungi(fungus,species,fertility)) end
			if exchange>0 then seed_age=16200 end
		end
		if f=="tree_seedling" and age>=seed_age and h.canopy<1.5 then
			if change(p,species and species.."_young" or "young_tree") then
				if exchange>0 then nutrients(p,-exchange) end
				return true
			end
			return false
		end
		if f=="young_tree" and age>=86400 and h.canopy<2 then return change(p,species and species.."_mature" or "mature_tree") end
		if f=="mature_tree" then
			if age>=259200 then return change(p,"deadwood") end
			if age>=1800 and serial%10==0 then disperse(p,species and species.."_seedling" or "tree_seedling",serial) end
			if serial%5==0 then disperse(p,"litter",serial) end
		elseif record and not trees[k] then
			local lifetime=({shrubs=86400,grasses=21600,herbs=14400,ferns_mosses=43200,fungi=2400,aquatic=21600,lichens=86400})[record.group]
			if record.tags.saprotroph and (h.substrate=="deadwood" or h.substrate=="litter")
				and botany.suitable(k,h,season) then
				-- Advance only an existing natural substrate's finite clock;
				-- never grant the fungus a second nutrient payout of its own.
				local below=at(p,0,-1,0)
				if natural(below,node(below)) and permitted(below) then
					local wood=api.get_meta(below)
					local limit=h.substrate=="deadwood" and 7200 or 1800
					wood:set_string("succ_age",tostring(math.min(limit,number(wood,"succ_age",limit)+math.min(dt,PERIOD))))
				end
			end
			if age>=lifetime then
				local remains="litter"
				if record.group=="fungi" or h.water>0 or h.substrate=="bark" or h.substrate=="deadwood" or h.substrate=="litter"
					or (diversity and diversity.is_rock(node(at(p,0,-1,0)))) then remains=nil end
				return change(p,remains)
			end
			if age>=7200 and h.water==0 and ground(at(p,0,-1,0)) and h.canopy<1.5 and (p.x*7+p.z*11)%23==0 then
				local th={}; for field,value in pairs(h) do th[field]=value end; th.include_trees=true
				-- The same catalogue selector is the source of all ten trees;
				-- skip non-tree results without changing its deterministic order.
				local recruit=botany.choose(p,th,season)
				if recruit and trees[recruit] then return change(p,recruit) end
			end
			if age>=900 and serial%3==0 then disperse(p,k,serial) end
		elseif diversity and diversity.is_worldgen_flora(k) and not trees[k] then
			if age>=7200 and h.canopy<1.5 and (p.x*7+p.z*11)%23==0 then
				local recruit=diversity.choose_tree(p,h)
				if recruit then return change(p,recruit) end
			end
			if k=="clover" and age>=900 then
				local below=at(p,0,-1,0)
				local soil=api.get_meta(below)
				local fixed=number(soil,"succ_fixed_nitrogen",2)
				-- At most two nitrogen additions per support, across deaths and
				-- restart. No endlessly farmable item or per-tick fertilizer loop.
				if fixed<2 and fertility<4 and permitted(p) and permitted(below) then
					nutrients(p,1); soil:set_string("succ_fixed_nitrogen",tostring(fixed+1))
				end
			end
			if age>=21600 then
				if diversity.is_rock(node(at(p,0,-1,0))) then return change(p,nil) end
				return change(p,"litter")
			end
			if age>=900 and serial%3==0 then disperse(p,k,serial) end
		elseif k=="spring_greens_patch" or k=="autumn_mushrooms_patch" then
			if age>=900 and serial%3==0 then disperse(p,k,serial) end
		elseif k=="meadow_grass" or k=="wildflowers" or k=="fern" then
			-- Occasional native woody recruitment in old meadows, not an instant forest.
			local recruitment_age = h.grass>=12 and fertility==0 and 14400 or 7200
			if k=="meadow_grass" and age>=recruitment_age and h.canopy<(diversity and 1.5 or 0.5) and h.moisture>=0.4
				and (p.x*7+p.z*11)%23==0 then
				local recruit=diversity and diversity.choose_tree(p,h) or (not diversity and "tree_seedling")
				if recruit then return change(p,recruit) end
			end
			if age>=(k=="wildflowers" and 14400 or 21600) then return change(p,"litter") end
			if age>=900 and serial%3==0 then disperse(p,k,serial) end
		end
		return false
	end
	local function nearby(p, fn)
		-- Nine cells, with one mutation at most. API input is never an unbounded radius.
		for x=-1,1 do for z=-1,1 do
			local q = at(p,x,0,z)
			if fn(q) then return true end
		end end
		return false
	end
	function S.forage(raw)
		local p = position(raw)
		if not p or not node(p) or not permitted(p) then return false end
		return nearby(p,function(q)
			local n = node(q)
			local k=kind(n)
			if not natural(q,n) then return false end
			if botany and botany.kind(k) then
				if not botany.browse(k,hearth.seasons and hearth.seasons.season() or "Summer")
					or (trees[k] and family(k)~="tree_seedling") then return false end
			elseif diversity then if not diversity.edible(k) then return false end
			elseif k~="meadow_grass" and k~="fern" then return false end
			if hearth.seasons and not hearth.seasons.available(k) then return false end
			if not change(q,nil) then return false end
			api.get_meta(q):set_string("succ_next",tostring(os.time()+300))
			return true
		end)
	end
	function S.deposit(raw)
		local p = position(raw)
		if not p or not node(p) or not permitted(p) then return false end
		return nearby(p,function(q)
			local n = node(q)
			if not n or n.name~="air" then return false end
			if number(api.get_meta(q),"succ_next")>os.time() then return false end
			if not change(q,"dung") then return false end
			api.get_meta(q):set_string("succ_next",tostring(os.time()+PERIOD))
			return true
		end)
	end
	function S.step(dtime)
		if type(dtime)~="number" or dtime~=dtime or dtime<0 then return 0 end
		elapsed=math.min(S.INTERVAL,elapsed+dtime)
		if elapsed<S.INTERVAL then return 0 end
		elapsed=0 -- Never replay a stalled frame's backlog.
		local players = api.get_connected_players()
		if #players==0 then seen,ring,ring_index={},{},1; return 0 end
		local now, work = os.time(), 0
		local side = S.RADIUS*2+1
		for _=1,S.BUDGET do
			player_index=player_index%#players+1
			local p = position(players[player_index]:get_pos())
			if p then
				local index = math.floor(cursor/#players)%(side*side)
				local x,z = index%side-S.RADIUS, math.floor(index/side)-S.RADIUS
				for y=6,-5,-1 do
					local q = at(p,x,y,z)
					-- At most twelve visual swaps per probe (96/second globally).
					-- Includes legacy mapgen leaves above the first natural ground.
					if hearth.seasons then
						local current = node(q)
						if current then hearth.seasons.reconcile(q,current,now) end
					end
					if diversity then diversity.bootstrap(q,node(q)) end
					local sub=botany and substrate(q)
					if ground(at(q,0,-1,0)) or sub then
						observe(q,now)
						-- Visit an epiphyte and its support in the SAME bounded
						-- column. Stopping above deadwood would freeze its clock.
						if not sub or (sub.substrate~="bark" and sub.substrate~="deadwood" and sub.substrate~="litter") then break end
					end
				end
			end
			cursor=(cursor+1)%(side*side*#players)
			work=work+1
		end
		return work
	end
	api.register_globalstep(S.step)
	local reload_nodes = {"hearth:grass", "hearth:soil"}
	if botany then reload_nodes[#reload_nodes+1]="hearth:water_source" end
	if diversity then
		for k in pairs(diversity.grounds) do reload_nodes[#reload_nodes+1]=PREFIX..k end
		for k in pairs(diversity.rocks) do reload_nodes[#reload_nodes+1]=PREFIX..k end
		if botany then
			reload_nodes[#reload_nodes+1]=PREFIX.."log"
			for _,species in ipairs(diversity.species_order) do reload_nodes[#reload_nodes+1]=PREFIX..species.."_log" end
		end
	end
	for k in pairs(kinds) do reload_nodes[#reload_nodes+1]=PREFIX..k end
	if hearth.seasons then
		for _, name in ipairs(hearth.seasons.names()) do reload_nodes[#reload_nodes+1]=name end
	end
	api.register_lbm({name="hearth:succession_loaded", label="Pause natural succession across unloading",
		nodenames=reload_nodes, run_at_every_load=true,
		action=function(p)
			seen[key(p)]=nil
			if ground(p) then seen[key(at(p,0,1,0))]=nil end
			if botany then
				seen[key(at(p,0,1,0))]=nil
				local component=api.get_meta(p):get_string("succ_component")
				if component~="" then seen[component]=nil end
			end
		end})
	return S
end