Full codebase audit: 21 security/robustness fixes, 328 tests across 4 packages

Security & economy:
- Credit()/Debit() reject non-positive amounts (closes infinite-money exploit)
- Lottery ticket purchase uses in-transaction count check (closes TOCTOU race)
- Arena bail channel ownership prevents double-close panic
- Entry.ID validated before exec.Command in fetch-esteemed
- Internal errors no longer leaked to users (forex, esteemed)

Robustness:
- safeGo() panic recovery added to 17 goroutine launch sites across 14 plugins
- db.Close() added and called on shutdown
- Miniflux mutex pattern fixed (snapshot-under-lock)
- Silently ignored DB/JSON errors now logged (lottery_db)

Performance:
- Added indexes: idx_arena_runs_user(user_id, status), idx_euro_bal_user(user_id)

UX:
- Empty !buy args shows usage instead of "No item matching ''"
- "Failed to load character" now suggests !adventure

Test coverage:
- internal/util/parser_test.go (19 tests: XP, levels, progress bar, commands, parsing)
- internal/crypto/crypto_test.go (12 tests: encrypt/decrypt, HMAC, ParseKey)
- internal/plugin/helpers_test.go (30 tests: formatNumber, calc, lottery, chat perks)
- internal/plugin/audit_fixes_test.go (25 tests: safeGo, bail channels, error leaks, overflow)
- internal/db/db_test.go (4 tests: Init, Close, schema indexes)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/plugin/lookup.go

@@ -63,11 +63,11 @@ func (p *LookupPlugin) OnMessage(ctx MessageContext) error {
 	default:
 		return nil
 	}
-	go func() {
+	safeGo("lookup-handler", func() {
 		if err := handler(ctx); err != nil {
 			slog.Error("lookup: handler error", "err", err)
 		}
-	}()
+	})
 	return nil
 }
 
@@ -210,14 +210,14 @@ func (p *LookupPlugin) handleDefine(ctx MessageContext) error {
 			if !antStarted {
 				antStarted = true
 				antLang := lang
-				go func() {
+				safeGo("lookup-antonyms", func() {
 					ants, err := p.dict.Antonyms(wordLower, antLang)
 					if err != nil {
 						antCh <- antResult{}
 						return
 					}
 					antCh <- antResult{ants: ants}
-				}()
+				})
 			}
 		}