Complete the overworld foundation

Port forced movement (turn delays, bumps, ice, currents, pits), dynamic
return warps, elevators, Surf, Cut, Strength and cycling rules, working
map blocks with changeblock/changemapblocks, and the remaining NPC
movement types and movement commands.

Add tileset animation from the ROM's command tables, grass sprite
priority and special map palettes; room decorations with ownership, the
bedroom PC and save migration; and Key Items access to the Bicycle.

Fourteen original-engine traces compare positions, facing, actors, event
flags and scripted poses. Tile animation matches original VRAM for four
tilesets, and LoadMapPals matches 192 palette cases. skyfall_top now
keeps the $60 sprite offset its step function leaves behind.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -34,7 +34,7 @@ flowchart LR
 | `src/reference`, `src/emulator` | Original-game reference, excluded from the native build                                         |
 | `reference/public`              | Licensed emulator files for the reference build only                                            |
 
-`GameRuntime` is a lifecycle interface, not an emulator contract. Native state is validated JSON, schema version 3. It holds the map, position, facing, name/avatar, player ID and in-game tile count; event and engine flags and sprite variables; scene values, phone contacts, a queued special call, the rival's name, the weekday offset and DST flag; positions of objects that scripts moved; and the party, bag, Pokédex sets and money. Early version-3 backups without a money field migrate to the starting balance. It contains no graphics, music, dialogue, GB memory or ROM bytes. Versions 1 and 2 migrate with new-game defaults. Party Pokémon are validated by recomputing their stats from the ROM. The backup envelope retains the historical `coreId` field; native backups use it for their runtime/schema ID.
+`GameRuntime` is a lifecycle interface, not an emulator contract. Native state is validated JSON, schema version 3. It holds the map, position, facing, name/avatar, player ID and in-game tile count; event and engine flags and sprite variables; scene values, phone contacts, a queued special call, the rival's name, the weekday offset and DST flag; positions of objects that scripts moved; and the party, bag, Pokédex sets, money and room decoration slots. Older saves without decorations migrate to the original bed and Town Map poster. Decoration imports validate slot categories, ownership and unique doll placement. Early version-3 backups without a money field migrate to the starting balance. It contains no graphics, music, dialogue, GB memory or ROM bytes. Versions 1 and 2 migrate with new-game defaults. Party Pokémon are validated by recomputing their stats from the ROM. The backup envelope retains the historical `coreId` field; native backups use it for their runtime/schema ID.
 
 Saves made during an unfinished walk or jump retain its source tile and completed step count, so loading cannot skip a landing event or map transition. Directional mats wait for exit input; doors, stairs and caves force an animated downward step after arrival.
 
@@ -49,3 +49,24 @@ Asset caches and the ROM reader remain in memory for lazy extraction. Neither RO
 The native viewport follows its available CSS dimensions and draws additional world tiles at a bounded pixel resolution. Beyond a map's edge it draws the connected map with the current tileset, as the original connection strips do, and the border block elsewhere. Resizing also redraws paused sessions. The local minimap caches terrain from the loaded map and updates its marker from the same world position used by the player; the Map tab shares that view. It is a current-area map, not a full region atlas. Leaving Game pauses the session and releases held input; returning requires explicit play. The reference player retains its own fixed-screen styling.
 
 `game/battle` now holds the native battle core and ROM-backed battle tables. Browser tests cover the overworld-to-battle flow using a test-only encounter fixture; Route 29 uses ROM encounter tables. Trainer battles share that core, with ROM trainer decoders, the trainer's send-out and switch AI, and explicit AI support checks. Map trainers (sight and talk) are started by `game/world` and run the ROM's own trainer scripts. Battles receive the script's draft party, bag and Pokédex, so a catch, a thrown ball or a nickname commits only with the script that started the battle. Introduce future modules with working features: `game/audio`, then `features/link` and `features/walking`. Party and bag models live in `game/party`; scripts change them only on their draft state. Rules must not import UI/browser modules. Transports and step providers must not write directly into world state.
+
+
+The overworld extension keeps player travel mode, backup-warp data and Flash
+state in version-3 saves, with defaults for older saves. Forced terrain and
+turn-in-place timing run through the idle movement path. Dynamic warps and
+elevators retain their return destination. Block mutations use a per-map working
+copy and a revision counter, so rollback and the minimap see the same terrain.
+Surf, Cut and Strength use the ROM scripts. Start/Select opens the Key Items
+menu, pausing overworld ticks while choosing the Bicycle. The bedroom PC edits
+decorations on the script draft and reloads the room when the menu commits.
+The wall/poster Town Map is a ROM-backed canvas presented by a script effect.
+
+`TilesetAnimator` translates the ROM animation command tables, advancing two
+video frames per overworld tick. It owns mutable graphics separately from the
+asset cache. The renderer records background color indices for grass sprite
+priority and applies special tileset palettes. Animation comparisons cover
+Johto, Ice Path, restless Ilex Forest and Tin Tower. The live forest engine
+flag selects the Celebi animation; the later story remains gated. Palette
+comparisons execute the original LoadMapPals routine across 192 cases.
+Movement traces compare event flags and check destinations across map-entry
+boundaries; controlled scenes also compare scripted pose visibility and lift.