Ship-audit P0/P1 sweep on open5e: prose, combat math, UX hygiene

P0 — actual bugs:
- eldritch_blast: SRD-imported "Whatever" placeholder leaked to players;
  overlay added in dnd_spells_data.go.
- Battle Master disarming_attack + parry: math.Max on multiplicative
  DamageReduct was a no-op vs the 1.0 default. Switched to *= and added
  regression tests covering the stacking case too.
- Extended TestSpellDescriptionsAreJargonFree to catch "Whatever",
  trailing ellipses, mid-word truncation, and empty-size phrases. This
  surfaced 4 more genuinely-broken SRD descriptions (find_familiar,
  clairvoyance, glyph_of_warding, teleportation_circle); all now
  overlayed in dnd_spells_data.go.

P1 — UX hygiene:
- Setup completion now nudges new casters toward !spells/!cast.
- Magic-item attunement vocab unified to "bond" everywhere user-facing;
  renamed the Treasures sheet section to avoid clashing with the bond
  vocab.
- Ambient DM footers stripped of "Threat +N" / "Supplies −N SU" hidden-
  meter leakage; verb-form footers instead.
- !expedition status defaults to a days-left + threat-label summary;
  raw SU / threat-out-of-100 / zone-stack / roll-modifier moved behind
  `!expedition status --debug`.
- !zone taunt/compliment help text dropped the "(mood −10)" / "(mood +5)"
  numerics that turned the hidden TwinBee-mood mechanic into a min/max
  knob.
- TwinBee pronoun pass: switched she/her to singular they on the two
  surfaces I touched plus achievements.bj_beat_twinbee.

P1 — correctness/scale:
- adventure_shop curio purchase now guards the euro.Debit bool return
  before inventory grant + pot cut; the GetBalance preflight isn't
  enough since a concurrent blackjack/lottery debit can slip the balance
  across BLACKJACK_DEBT_LIMIT between read and write.
- equipMagicItem reordered: remove inventory item BEFORE equip, with a
  best-effort rollback if equip fails. The prior order left a dup
  window if the inventory delete tripped on a transient DB error.
- magicItemsByRarityCache promoted to sync.Once — concurrent cold-start
  loot rolls otherwise raced on the lazy assignment.

Stale-audit verifications (no code change needed):
- light / druidcraft / water_walk overlays already exist and win the
  SRD merge — the broken raw text never reaches players.
- bootstrapPhase5BHPRefresh is already wired at adventure.go:228.

Deferred:
- combatantsForSession per-turn 6-load DB chatter (perf P1-A): touches
  the hot combat path; needs its own test pass before shipping. Tracked
  in memory at project_combat_session_cache_deferred.

go vet clean; go test -race ./... green (229s).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/adventure_shop.go

@@ -1301,7 +1301,17 @@ func (p *AdventurePlugin) resolveShopCurioChoice(ctx MessageContext, interaction
 		return p.SendDM(ctx.Sender, fmt.Sprintf("You need €%.0f for %s but only have €%.0f.", price, match.Name, balance))
 	}
 
-	p.euro.Debit(ctx.Sender, price, "shop_curio")
+	// Guard the Debit return: GetBalance above is a snapshot read, but
+	// the debt-limit check inside Debit (BLACKJACK_DEBT_LIMIT) can refuse
+	// the write if a concurrent debit (blackjack, lottery, etc.) has
+	// slipped the balance across the limit between read and write.
+	// Without this guard the curio would be granted on a refused debit.
+	if !p.euro.Debit(ctx.Sender, price, "shop_curio") {
+		p.pending.Store(string(ctx.Sender), interaction)
+		return p.SendDM(ctx.Sender, fmt.Sprintf(
+			"Tried to charge €%.0f for %s, but the purse refused — your balance moved out from under us. Try again.",
+			price, match.Name))
+	}
 	if potCut := int(math.Round(price * 0.05)); potCut > 0 {
 		communityPotAdd(potCut)
 		trackTaxPaid(ctx.Sender, potCut)