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/features/characters/sheet/ResourcesSection.tsx

@@ -1,6 +1,7 @@
 import { useState } from 'react';
 import { newId } from '@/lib/ids';
 import { getSystem, applyRest } from '@/lib/rules';
+import { spendResource, regainResource } from '@/lib/mechanics';
 import type { CharacterResource } from '@/lib/schemas';
 import { Button } from '@/components/ui/Button';
 import { Input, Select } from '@/components/ui/Input';
@@ -61,12 +62,12 @@ export function ResourcesSection({ c, update }: SectionProps) {
           {c.resources.map((r) => (
             <li key={r.id} className="flex items-center gap-2 rounded-md border border-line bg-panel px-3 py-2">
               <Input className="h-8 flex-1" value={r.name} onChange={(e) => patch(r.id, { name: e.target.value })} aria-label="Resource name" />
-              <Button size="icon" variant="ghost" onClick={() => patch(r.id, { current: Math.max(0, r.current - 1) })} aria-label="Spend">−</Button>
+              <Button size="icon" variant="ghost" onClick={() => { const res = spendResource(c, r.id); if (res.ok) update(res.patch); }} aria-label="Spend">−</Button>
               <span className="w-12 text-center text-sm">
                 <span className="font-medium text-ink">{r.current}</span>
                 <span className="text-muted">/{r.max}</span>
               </span>
-              <Button size="icon" variant="ghost" onClick={() => patch(r.id, { current: Math.min(r.max, r.current + 1) })} aria-label="Regain">+</Button>
+              <Button size="icon" variant="ghost" onClick={() => { const res = regainResource(c, r.id); if (res.ok) update(res.patch); }} aria-label="Regain">+</Button>
               <NumberField className="w-14" value={r.max} min={0} onChange={(v) => patch(r.id, { max: v, current: Math.min(v, r.current) })} aria-label="Max" />
               <Select className="w-auto py-1 text-xs" value={r.recovery} onChange={(e) => patch(r.id, { recovery: e.target.value as CharacterResource['recovery'] })}>
                 {(['short', 'long', 'daily', 'none'] as const).map((k) => (