fix(M01): correct ADT filename coordinate axes

Work-Package: M01-FND-COORD-TILE-AXIS-002
Agent: sindo-main-codex
Tests: coordinate mapper, M00 calibration, baseline manifest, coordination and documentation gates passed
Fidelity: Azeroth_31_49 raw MCNK origins and OpenRealm confirm filename X from world Y and filename Y from world X

docs/adr/0001-canonical-world-coordinates.md

@@ -2,7 +2,7 @@
 
 - Status: Accepted for M01 contract implementation
 - Date: 2026-07-13
-- Work package: `M01-FND-COORDS-001`
+- Work packages: `M01-FND-COORDS-001`, corrected by `M01-FND-COORD-TILE-AXIS-002`
 - Decision owners: M01 foundation/integration owners
 
 ## Context
@@ -45,8 +45,8 @@ ADT_TILE_SIZE_YARDS = 1600 / 3
 ADT_TILES_PER_MAP_AXIS = 64
 WOW_WORLD_HALF_EXTENT_YARDS = 32 * ADT_TILE_SIZE_YARDS
 
-tileX = floor(32 - canonical.X / ADT_TILE_SIZE_YARDS)
-tileY = floor(32 - canonical.Y / ADT_TILE_SIZE_YARDS)
+tileX = floor(32 - canonical.Y / ADT_TILE_SIZE_YARDS)
+tileY = floor(32 - canonical.X / ADT_TILE_SIZE_YARDS)
 ```
 
 `AdtTileCoordinate(tile_x, tile_y)` always means the indices in
@@ -55,9 +55,9 @@ south-east extent produces index 64 and remains diagnosable as out of bounds.
 Normal valid indices are 0 through 63.
 
 An `AdtTileLocalPosition` is measured east and south from the tile's
-north-west corner. An `AdtChunkCoordinate` uses `chunk_x` south and `chunk_y`
-east, with valid indices 0 through 15. These direction names avoid pretending
-that ADT file axes are Godot X/Z axes.
+north-west corner. Filename `tile_x` and MCNK `chunk_x` grow east; filename
+`tile_y` and MCNK `chunk_y` grow south, with valid indices 0 through 15. These
+direction names avoid pretending that ADT file axes are Godot X/Z axes.
 
 ### ADT placement fields
 
@@ -97,6 +97,17 @@ normalize the value to `[-PI, PI)` without adding an offset.
 This identity applies to world-facing yaw only. It does not apply to M2/WMO
 asset axes or placement Euler triples.
 
+### Contract version 2 correction evidence
+
+Contract version 1 incorrectly calculated filename `tile_x` from canonical X
+and `tile_y` from canonical Y. The private WotLK corpus contains the observed
+Elwynn point in `Azeroth_31_49.adt`, SHA-256
+`18185B5FAC9566D9C57A9C19ABD75F108370D1795639B6077167C0EFD3672FAE`; the
+transposed `Azeroth_49_31.adt` does not exist. Raw MCNK headers in that file
+show `indexX` decreasing world Y (east) and `indexY` decreasing world X (south).
+OpenRealm independently calculates filename X from world Y and filename Y from
+world X. Contract version 2 corrects the formulas before any consumer migration.
+
 ## Alternatives considered
 
 ### Make renderer coordinates canonical
@@ -140,6 +151,8 @@ grid ownership rules.
   checkpoints within `0.002` yard.
 - Server, ADT placement, Godot and tile-local conversions round-trip.
 - Exact center, tile, chunk and world-extent boundaries have explicit tests.
+- The observed Elwynn position resolves to the real `Azeroth_31_49.adt` file;
+  MCNK `(0,0)` to `(15,15)` origins confirm X-east and Y-south chunk growth.
 - World-yaw normalization and round-trip cases cover cardinal angles and wrap.
 
 ## References