V2 Phase 2: spell + resource enforcement (sheet → combat → live)

The Slice-0 vertical that proves the enforcement architecture end-to-end.

- kernel: castSpell (slot consumption + concentration set/replace, upcasting,
  warlock pact slots), spendResource/regainResource, rollDeathSave — pure
  functions returning Partial<Character> patches. 13 unit tests.
- applyRest now ends concentration on any rest (+ test).
- character sheet SpellcastingSection: per-spell Cast button, concentration
  banner with Drop, concentration markers; ResourcesSection −/+ routed through
  the kernel.
- player MyCharacterPanel: castable spell list + concentration banner, so a
  seated player casts and it broadcasts via the existing playerPatch flow.
- live sync: partialCharacterDiffSchema carries concentration; GM applies it;
  playerCharacterSchema mirrors slots/concentration/resources (PC-only) and the
  player-facing AC now respects equippedArmor. Wire round-trip test added.

Verified live: casting decrements the right slot, switching concentration logs
"Concentration on X ends", banner + Drop render. Build + 258 tests green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/mechanics/index.ts

@@ -11,9 +11,13 @@ import { normalizeMonsterDefenses } from './normalize/monsterDefenses';
 import type { ArmorMechanics, DamageDefenses, SpellMechanics } from './types';
 
 export * from './types';
+export type { EnforceResult } from './result';
 export { normalizeSpell5e, normalizeSpellPf2e } from './normalize/spell';
 export { normalizeArmor5e } from './normalize/armor';
 export { normalizeMonsterDefenses } from './normalize/monsterDefenses';
+export { castSpell, dropConcentration } from './cast';
+export { spendResource, regainResource } from './resources';
+export { rollDeathSave, type DeathSaveOutcome } from './deathSaves';
 
 let spellMechCache: Map<string, SpellMechanics> | null = null;
 let armorMechCache: Map<string, ArmorMechanics> | null = null;