Open Route 30 with map trainers and multi-Pokémon trainer battles

Map trainers run the ROM's TalkToTrainerScript and SeenByTrainerScript.
_CheckTrainerBattle runs before tile events at the end of each step and
on idle ticks; TrainerWalkToPlayer builds wMovementBuffer natively, and
writeobjectxy keeps the trainer where it stopped. The interpreter gains
the trainer header commands, wRunningTrainerBattleScript and hidden
items (HiddenItemScript).

Trainers with several Pokémon send out the next one through
EnemyPartyMonEntrance and FindMonInOTPartyToSwitchIntoBattle, including
its BattleRandom fallback. AI_SwitchOrTryItem, CheckAbleToSwitch and
AI_Switch are translated with their original bugs, and wPlayerUsedMoves
is recorded. The Shift-mode switch offer, trainer items, Pursuit on a
switch, Perish Song and Spikes remain refused.

Route 30 and its Berry house are enabled; Mr. Pokémon's house and
Route 31 stay closed. A refused trainer sighting does not restart until
the player moves, so a rollback cannot trap the player in view.

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

docs/PLAN.md

@@ -49,7 +49,7 @@ The emulator-backed prototype is now at `/reference.html`. The default applicati
 
 ## Done: Route 29 and Cherrygrove City
 
-- Route 29, its Route 46 gate, Cherrygrove City and its five buildings are enabled. Route 30 and Route 46 remain closed.
+- Route 29, its Route 46 gate, Cherrygrove City and its five buildings are enabled. Route 46 remains closed.
 - Item balls run the ROM's `FindItemInBallScript`. Fruit trees run `FruitTreeScript`, with picked trees saved and regrown by a native `CheckDailyResetTimer` that clears the daily engine flags once per game day.
 - The Pokémon Center nurse runs `PokecenterNurseScript`: `HealParty` (with `ComputeMaxPP`'s PP Up clamp), `CheckPokerus` and the phone-call checks. Entering a Center from a town or route records the whiteout spawn, as `EnterMapWarp` does.
 - Standard Poké Marts run `pokemart` natively from `StandardMart`, `BuyMenu` and `SellMenu`: stock from the ROM's `Marts` table, `ItemAttributes` prices, half-price selling and the original texts, with keyboard, D-pad and pointer menus. Special mart types remain refused.
@@ -65,11 +65,21 @@ The emulator-backed prototype is now at `/reference.html`. The default applicati
 - Native move scoring for Basic, Setup, Types, Offensive, Opportunist, Aggressive, Cautious, Status and Risky, with deterministic tie selection and the original pre-variation damage estimate. Smart remains refused.
 - Scripted single-Pokémon trainer battles support the challenge, sending out, RUN refusal, experience, win/loss text and prize money, including Amulet Coin. Script results, party changes and rewards commit together; interrupted saves replay from committed state.
 - Local-ROM tests and Chromium/WebKit tests exercise Youngster Joey through a test-only script. No new maps or trainer encounters are enabled in normal play.
-- Next: Smart AI, trainer party switching/items, trainer sight lines and normal trainer-object scripts, then the rival and Route 30 story. The rival remains refused because Smart AI is not yet translated.
+- Next: Smart AI, trainer items and player switching, then the rival and the rest of the Route 30 story. The rival remains refused because Smart AI is not yet translated.
+
+## Implemented: Route 30 trainers
+
+- Map trainers run the ROM's `TalkToTrainerScript` and `SeenByTrainerScript`. `_CheckTrainerBattle` runs before tile events after each step and on every idle tick: the first unbeaten trainer facing the player in line within its sight range spots them. The native `TrainerWalkToPlayer` path is played from `wMovementBuffer`, and `writeobjectxy` keeps the trainer where it stopped (saved with the map's moved objects).
+- New script commands: `loadtemptrainer`, `trainertext`, `trainerflagaction`, `scripttalkafter`, `endifjustbattled`, `checkjustbattled`, `writeobjectxy`, `encountermusic` (silent) and `loadmem` for `wRunningTrainerBattleScript`.
+- Trainers with several Pokémon: `HandleEnemyMonFaint` sends out the next one through `EnemySwitch_SetMode`, `FindMonInOTPartyToSwitchIntoBattle` (including its `BattleRandom` fallback) and `NewEnemyMonStatus`. `AI_SwitchOrTryItem` translates `CheckAbleToSwitch` with its original bugs (every matchup uses the enemy's move type; the quarter-HP test rotates bits) and `AI_Switch`. The player's used moves are recorded for it.
+- Hidden items (`BGEVENT_ITEM`) run `HiddenItemScript`.
+- Route 30 and its Berry house are enabled. Mr. Pokémon's house and Route 31 stay closed; Youngster Joey (after the Egg) needs phone registration and stays hidden until then, as in the original.
+- A refused trainer script does not restart until the player moves, so a rollback cannot trap the player in a trainer's sight.
+- A local stress run of 1,080 Route 30 battles (three starters, four levels, three times of day, both trainers and wild encounters) found one refusal: Chikorita's Reflect at level 12 (`screen`, not yet ported).
 
 ## In progress: native battles
 
-The battle core, ROM tables, encounter hooks, battle UI and whiteout hooks are present. Unit tests cover wins, escape, loss, experience and move learning; reference tests compare damage and type effectiveness. Browser tests drive a test-only wild encounter through the real UI: victory with level-up and move learning, escape, whiteout, keyboard and on-screen D-pad menu navigation, mid-battle backup restore, and rollback of unsupported effects. Real Route 29 encounters now use the ROM's encounter tables. Capture, switching, items in battle, trainer battles and the rest of the opening quest remain unfinished.
+The battle core, ROM tables, encounter hooks, battle UI and whiteout hooks are present. Unit tests cover wins, escape, loss, experience and move learning; reference tests compare damage and type effectiveness. Browser tests drive a test-only wild encounter through the real UI: victory with level-up and move learning, escape, whiteout, keyboard and on-screen D-pad menu navigation, mid-battle backup restore, and rollback of unsupported effects. Real Route 29 encounters now use the ROM's encounter tables. Capture, player switching, items in battle and the rest of the opening quest remain unfinished.
 
 This is still not a complete new game. Party/bag/Pokégear menus, story progression beyond Cherrygrove, decorations, animated terrain, surfing and audio remain unfinished. Save slots, a Johto/Kanto atlas, Pokédex records, online Link, friends and real-world steps come later.
 
@@ -77,7 +87,7 @@ This is still not a complete new game. Party/bag/Pokégear menus, story progress
 
 Map headers, location names, connection offsets, connected-border drawing, coordinate events, scene scripts, map callbacks and scripted movement are in place (see above). Next: enable connected transitions as their maps are ported; add dynamic warps, elevators, ice, currents, remaining forced movement, surfing, cycling, cut trees and boulders. Player turn timing still needs a reference comparison.
 
-Port decorations, tile changes (`changeblock`), the remaining NPC movement types (followers, bouncing, Strength boulders), trainer sight lines and the remaining movement commands. Complete terrain animation, layering and special palettes. Record deviations from the original until a comparison test closes them.
+Port decorations, tile changes (`changeblock`), the remaining NPC movement types (followers, bouncing, Strength boulders) and the remaining movement commands. Complete terrain animation, layering and special palettes. Record deviations from the original until a comparison test closes them.
 
 Acceptance: representative outdoor/interior/cave/connected-map traces produce matching positions, collisions, transitions and event changes in native and reference engines. Do not enable an area merely because its image can be decoded.
 
@@ -87,7 +97,7 @@ Introduce native player, party, Pokémon, inventory, money and quest models. Rea
 
 Expand script calls, choices, scene state, inventory commands and native special handlers. Translate routines reached through assembly calls into explicit native services; never fall back to emulator execution in the shipping game.
 
-Meeting Mom, Elm's introduction, the starter, the aide's Potion, Route 29 and Cherrygrove run now. Next: trainer sight lines and trainer battles, Route 30 and Mr. Pokémon, the Mystery Egg round trip with the catching tutorial and the rival battle; then the introduction's naming and clock screens.
+Meeting Mom, Elm's introduction, the starter, the aide's Potion, Route 29, Cherrygrove and Route 30's trainers run now. Next: Mr. Pokémon's house, the Mystery Egg round trip with the catching tutorial and the rival battle; then the introduction's naming and clock screens.
 
 Complete and validate the native battle engine: deterministic randomness, stats, move selection, accuracy/critical checks, damage, status, turn order, switching, fainting, experience, capture and rewards. Compare controlled seeds and states with the original, including integer rounding and overflow behavior.