Fetch a markdown reference guide that teaches the conventions for authoring a specific entity type in a specific ruleset. Returns the full markdown body, including front-matter metadata (ruleset, entityType, version) at the top. Published for 5e24: { entityType: 'monster' } — monster stat-block authoring (field map, AC base calc, CR-to-level-to-XP table, action types, spell formatting, resistances/immunities, keywords, high-PB adjustment, worked example), authored via vault_create_character + vault_update_character; { entityType: 'rule' } — classes / species / backgrounds / feats / abilities (the type taxonomy, the parent→Ability grant model, type-specific section fields, and the shared mechanics blocks: proficiencyChoices, spellChoices, spellListChoices, preparedSpells, freeCast, uses, ruleChoice, statBonuses), authored via vault_create_rule + vault_update_rule; { entityType: 'spell' } — the 5e24 Spell Detail header (casting time / range / area / components / duration), the `categories` (Class(es)) membership convention, and the damage/healing/effect mechanics blocks, authored via vault_create_spell + vault_update_spell. Call this BEFORE authoring the matching entity so the result follows the established conventions instead of inferring shape from one-off samples. Returns a 'not found' tool error when the requested entityType / rulesetCode combination does not have a published guide yet.