feat(mods): expose read-only battle snapshots

docs/modding.md

@@ -235,6 +235,33 @@ not need generation-specific badge, terrain, bike, fishing, or field-move
 logic. Action lists are extensible; callers should render the records they
 understand and ignore unknown ids rather than assuming a fixed list length.
 
+## Read-only battle snapshots
+
+`mod.battle:snapshot()` returns `nil` outside a battle and a copied battle
+record while one is active. Gen 1 (Red, Blue, and Yellow) and Gold expose the
+same core fields:
+`revision`, `kind`, `catchable`, `prompt`, `message`, `turn`, `player`,
+`enemy`, `party`, `moves`, and `items`. Pokémon, moves, messages, and items in
+the result are detached records; changing them cannot change the battle.
+`revision` stays stable while the visible battle context is unchanged and
+advances when it changes, so a UI can skip rebuilding an identical view.
+
+Pokémon records contain `species`, `name`, `level`, `hp`, `maxHp`, `status`,
+and `active` (plus `slot` in `party`). Move records contain `slot`, `id`,
+`name`, `pp`, `maxPp`, `type`, `power`, `accuracy`, and `disabled`. Gen 1 also
+reports the actual ruleset-aware `displayPower`, `hitChance` percentage, and
+`effectiveness` multiplier (`10` neutral, `20` super-effective, `5`
+resisted). Item rows contain `id`, `name`, `count`, `ball`, `needsTarget`, and
+an optional stock `catchChance` percentage.
+
+`prompt` describes the currently visible choice (`menu`, `moves`, `party`,
+`advance`, `safari`, or `mimic`) and is `locked` when another screen or battle
+phase owns input. Generation-specific features remain optional: Gen 1 includes
+battle medicine, balls, catch previews, Safari balls, and Mimic choices;
+Gold currently returns an empty `items` list rather than guessing at its
+pocketed PACK flow. Callers should ignore unknown fields and tolerate absent
+optional ones.
+
 ## Rendering pipelines
 
 Most registries hand the engine *content*. `render_pipelines` hands it