The mutation check of 2026-10-07: tools/high-tests/rig/mutants.py, one line of the production code changed at a time in a scratch copy of the tree, the suites that should
notice it run (heavy.sh 4G). Each row: the mutant, the suites that failed with the first failing checks (cut), the seconds the build and run took, and what the line does.

First run, the tree at 77ce12d with the working tree's rig files. Three rows (wiring-export-limit, wiring-altbiome-limit, export-cfg-no-mode) show passing checks of
their suite where the failing ones should be: the script took the first lines that say 'error'; the third run below has them right.
unmutated copy, altbiome-harness export-tests golden-tests high-tests import-tests tile-tests zone-tests: ALL PASSED (79 s)
wiring-patcher-call-removed    killed by high-tests: FAIL DynamicPatch's first call is PatchHighTerrain (it is UpdateGeometry) | FAIL a heightmap at Amount 81 (Auto): HighTerrain is active (the top 0 m) | FAIL a heightmap at Amount 81 (Auto): the groups that can be switched on here are (Character.InInterior and the methods that call it no, random events no, the ground rays no, the AI's navigation tiles no, altitude limits no, the V   (6 s)  # DynamicPatch's call of PatchHighTerrain
wiring-patcher-call-last       killed by high-tests: FAIL DynamicPatch's first call is PatchHighTerrain (it is UpdateGeometry) | FAIL the main menu after a high world, with a step that throws: no group is applied, no patch stands, HighTerrain is inactive   (7 s)  # PatchHighTerrain as DynamicPatch's last step, where an earlier step that throws skips it
wiring-export-limit            killed by export-tests: PASS 16-bit quantisation error <= half a step (worst 0.5 steps) | FAIL the export accepts 16384 px at Heightmap Amount 81 | FAIL 16384 amount=81 parses and is valid (the largest size and amount)   (10 s)  # a world export's heightmap amount limit (the schema's 81)
wiring-altbiome-limit          killed by altbiome-harness: PASS override parse errors reported, good parts kept: 'Bad' has no 'Name:' prefix; Mushroom: 'x' is not a number; Lantern: unknown field 'colour' (valid: enabled, chance, min, max, mindist, minedge, maxedge, minheight, maxheight,  | PASS an unreadable alt-biome blob: error, vanilla behaviour, the rest loads, the blob is kept | FAIL a world of land to 16170 m: every alt biome's 10000 m limit becomes 17170 m, the lower ones stay (0 of 32 lifted)   (28 s)  # the alt biomes' 10000 m limit on a sector's mean height, lifted with the patches
wiring-zoneregen-interior      killed by zone-tests: FAIL a high world: a player 4000 m up over a ground of 3900 m is not in a dungeon (the game's own rule says he is) | == final: an error finishes the zones the run had emptied and left waiting | == requests: refused where there is no world to regenerate, started, started over, and stopped by an error   (9 s)  # a player's 'inside a dungeon' in zone regeneration, by the patched rule
ray-guard-partial              killed by high-tests: FAIL client ZoneSystem.GetGroundHeight(1 parameter) without its 10000 m length: left exactly as it was, and the log names ZoneSystem.GetGroundHeight | FAIL client ZoneSystem.GetGroundHeight(1 parameter) without its 6000 m start: left exactly as it was, and the log names ZoneSystem.GetGroundHeight | FAIL client ZoneSystem.GetGroundHeight(1 parameter) with its start twice: left exactly as it was, and the log names ZoneSystem.GetGroundHeight   (7 s)  # the ground ray transpiler's all-or-nothing guard (both numbers found, not either)
upray-guard-partial            killed by high-tests: FAIL client ZoneSystem.GetGroundData without its 10000 m length: left exactly as it was, and the log names ZoneSystem.GetGroundData | FAIL client ZoneSystem.GetGroundData without its 5000 m origin: left exactly as it was, and the log names ZoneSystem.GetGroundData | FAIL client ZoneSystem.GetGroundData without the addition that puts the origin over the point: left exactly as it was, and the log names ZoneSystem.GetGroundData   (7 s)  # the same guard of the ground data and grass ray transpilers
blocker-guard-two              killed by high-tests: FAIL client ZoneSystem.IsBlocked with its 2000 m added twice: left exactly as it was, and the log names ZoneSystem.IsBlocked | FAIL server ZoneSystem.IsBlocked with its 2000 m added twice: left exactly as it was, and the log names ZoneSystem.IsBlocked   (7 s)  # the blocker transpiler's count (exactly one 2000 m found)
blocker-shape-guard            killed by high-tests: FAIL client ZoneSystem.IsBlocked's IL asked of a static method (ZoneSystem.GetZone): left exactly as it was, and the log names ZoneSystem.GetZone | FAIL client ZoneSystem.IsBlocked's IL asked of a method with two parameters (ZoneSystem.GetGroundHeight): left exactly as it was, and the log names ZoneSystem.GetGroundHeight | FAIL server ZoneSystem.IsBlocked's IL asked of a static method (ZoneSystem.GetZone): left exactly as it was, and the log names ZoneSystem.GetZone   (7 s)  # the blocker transpiler's check of the method's shape (an instance method with one Vector3)
hook-swapped                   killed by high-tests: FAIL the 31 hooks are the ones meant, by type, method, signature and patch: in the list only: [Pathfinding.FindGround(Vector3,Boolean,List`1,AgentSettings)|RaiseGroundDataRay|transpiler]; meant only: [Pathfinding.FindGround(Vector | FAIL Pathfinding.FindGround(Vector3,Boolean,List`1,AgentSettings): RaiseGroundDataRay changes it (86 -> 86 instructions) and finds all it expects   (7 s)  # the AI's FindGround hooked to the transpiler of another method's rays
hook-missing-teleport          killed by high-tests: FAIL 31 hooks in all: 15 for InInterior (its 3 overloads and 12 methods that call it), 2 events, 6 rays, 1 tile, 6 altitudes, 1 Valkyrie (30) | FAIL the 31 hooks are the ones meant, by type, method, signature and patch: in the list only: []; meant only: [Teleport.Interact(Humanoid,Boolean,Boolean)|RedirectInterior|transpiler] | FAIL 26 of the hooks are transpilers (the other five: the three overloads of InInterior, the AI's tile, the Valkyrie), each run on its own method (25)   (7 s)  # a caller of Character.InInterior left out of the hooks
wanted-off-is-auto             killed by high-tests: FAIL Off, Amount 5.01, Override All on: the patches are not wanted (got True) | FAIL Off, Amount 5.01, Override All on: 6 of the six toggles are wanted (none expected) | FAIL Off, Amount 5.01, Override All on: the Deep North weather asks at x and z exactly when the patches are wanted (no biome map)   (7 s)  # High Terrain Off that still patches a high world
wanted-on-needs-heightmap      killed by high-tests: FAIL On, no heightmap, Override All on: the patches are wanted (got False) | FAIL On, no heightmap, Override All on: 0 of the six toggles are wanted (all expected) | FAIL On, no heightmap, Override All on: the Deep North weather asks at x and z exactly when the patches are wanted (no biome map)   (7 s)  # High Terrain On that skips a world without a heightmap
bound-no-heightmap             killed by high-tests: FAIL Heightmap Amount 81 with no heightmap: the amount multiplies nothing, the land is the game's own (Bound.cs, Modes.cs), and it is not a high world (Auto) | FAIL a world without a heightmap: the Mountain biome's bound over the game's own base height, 0 m | FAIL base height -0.15: the game's Meadows and Plains formula is under the bound of a world without a heightmap too (0 units)   (7 s)  # the top of a world without a heightmap, taken as 0 m
mode-change-no-repatch         killed by high-tests: FAIL after bc h ht off: no group is applied, no patch stands, HighTerrain is inactive | FAIL after bc h ht off: the game's own rules: anything over 3000 m is inside a dungeon, and no event is told to a player over 3000 m | FAIL after bc h ht off: the Deep North weather asks at x and z no longer (UseZ True)   (7 s)  # a live change of the mode that does not switch the patches
mode-change-no-regen           killed by high-tests: FAIL bc h ht on in a world of Amount 2: nothing it lifts reaches an alt biome, and the zones are regenerated (2) | FAIL a word that is no mode changes nothing, and regenerates nothing (2) | FAIL a word that is no mode changes nothing, and regenerates nothing (2)   (7 s)  # a live change of the mode that leaves the zones as they were
serialize-writes-auto          killed by golden-tests high-tests: FAIL presets: 8 difference(s) | FAIL settings: 40 difference(s) | FAIL settings: 40 difference(s)   (12 s)  # Auto written to every world's settings
serialize-unknown-mode         killed by high-tests: FAIL High Terrain 9, which no mode is: read as Auto, said in the log, and the rest of the settings load   (7 s)  # a mode number no version knows, kept as it is
serialize-key-68               killed by high-tests: FAIL DataKey.HighTerrain is 69; the keys before it are numbered 0 to 67 as ever | FAIL no heightmap, disk, On: the bytes are the Auto world's with the key 69 and the value 1 put in (at byte -1) | FAIL no heightmap, disk, Off: the bytes are the Auto world's with the key 69 and the value 2 put in (at byte -1)   (30 s)  # the key 68, which is the wide sectors'
export-cfg-no-mode             killed by export-tests: PASS 16-bit quantisation error <= half a step (worst 0.5 steps) | FAIL a world in High Terrain Off exports 'High Terrain = Off' in the Heightmap section, and it wins over a config that says On | FAIL a world in High Terrain On exports 'High Terrain = On' in the Heightmap section, and it wins over a config that says Off   (17 s)  # the mode left out of an export's export.cfg
dump-no-mode                   killed by high-tests: FAIL the dump says High Terrain On, with no heightmap too | FAIL On over a heightmap: said once, as On   (7 s)  # bc info that does not say High Terrain On
schema-order                   killed by golden-tests high-tests: FAIL config: 3 difference(s) | FAIL it is the last of its section (a setting in the middle would move the order of the others in the file) | FAIL the config entry is bound, Auto, and ordered last in the section   (13 s)  # High Terrain moved from the end of its section
console-name                   killed by high-tests: FAIL the console has it as bc h ht, and a live change redoes the rules (LiveChange.Rules), not the world | FAIL bc h ht off: System.NullReferenceException: Object reference not set to an instance of an object. | FAIL bc h ht off: the running world is Off, and its zones are regenerated once (0)   (7 s)  # the console name of the setting
console-parse-old              killed by high-tests: FAIL and refuses a number (one that is a mode too), a list of names, a word that is no mode, and nothing: only a name   (7 s)  # the console reading a number or a list of names as a mode (Enum.Parse alone)
description-no-cost            killed by golden-tests high-tests: FAIL config: 1 difference(s) | FAIL its description says what each mode does and what Off costs, and names no version   (13 s)  # the setting's description without what Off costs
deepnorth-log-every-time       SURVIVED: every suite passed   (7 s)  # the Deep North transpiler that says so at every re-patch
update-note-wording            killed by high-tests: FAIL the menu again: inactive, and says the game's own rules apply again | FAIL On to Off (as a console change): inactive, and says the game's rules apply again   (7 s)  # the log line when a high world is left, with the old reason
26 of 27 mutants killed

Second run, the survivor above after DeepNorthLogTests was added (tools/high-tests/Toggles.cs), the tree at 7f855dd, a new scratch copy:
unmutated copy, high-tests: ALL PASSED (9 s)
deepnorth-log-every-time       killed by high-tests: FAIL client EnvMan.UpdateEnvironment: three runs of the transpiler say it once (3)   (7 s)  # the Deep North transpiler that says so at every re-patch
1 of 1 mutants killed

Third run, the tree at d69ddf7 (the failing checks first, and three more wiring mutants), a new scratch copy:
unmutated copy, altbiome-harness export-tests high-tests import-tests: ALL PASSED (43 s)
wiring-update-removed          killed by high-tests: FAIL a heightmap at Amount 81 (Auto): HighTerrain is active (the top 0 m) | FAIL and back to 81: HighTerrain is active (the top 0 m) | FAIL High Terrain On at Amount 81: HighTerrain is active (the top 0 m)   (7 s)  # PatchHighTerrain that does not tell HighTerrain the world's settings first
wiring-usez-store              killed by high-tests: FAIL a heightmap at Amount 81 (Auto): the Deep North weather asks at x and z (UseZ False) | FAIL and back to 81: the Deep North weather asks at x and z (UseZ False) | FAIL High Terrain On at Amount 81: the Deep North weather asks at x and z (UseZ False)   (7 s)  # DynamicPatch's store of the Deep North weather's x-and-z rule
wiring-export-limit            killed by export-tests: FAIL the export accepts 16384 px at Heightmap Amount 81 | FAIL 16384 amount=81 parses and is valid (the largest size and amount)   (10 s)  # a world export's heightmap amount limit (the schema's 81)
wiring-altbiome-limit          killed by altbiome-harness: FAIL a world of land to 16170 m: every alt biome's 10000 m limit becomes 17170 m, the lower ones stay (0 of 32 lifted)   (29 s)  # the alt biomes' 10000 m limit on a sector's mean height, lifted with the patches
serialize-read-ignored         killed by high-tests: FAIL no heightmap, disk, On: read back, the mode is Auto | FAIL no heightmap, disk, On: the world that reads it wants the patches as the one that wrote it did, to the same top, and says the same of itself | FAIL no heightmap, disk, On: saved again, the same bytes   (7 s)  # the saved mode read and thrown away
export-cfg-no-mode             killed by export-tests: FAIL a world in High Terrain Off exports 'High Terrain = Off' in the Heightmap section, and it wins over a config that says On | FAIL a world in High Terrain On exports 'High Terrain = On' in the Heightmap section, and it wins over a config that says Off   (16 s)  # the mode left out of an export's export.cfg
6 of 6 mutants killed

In all: 30 mutants, 29 killed at once, one (deepnorth-log-every-time) after the test that it showed was missing.
