chore: 🦋 add changeset

Author: jwyce

.changeset/tasty-mangos-sneeze.md

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+---
+'gungi.js': patch
+---
+
+🔧 prevent duplicate piece IDs in state transitions
+
+Addresses race conditions in rapid `load()` calls where same piece
+type/color could receive identical IDs, breaking game state integrity.
+
+- `applyCanonicalToMissingIds` used flawed conflict detection
+- Arata moves assigned same ID to both board and hand pieces
+- Race conditions during rapid state transitions
+
+Fixed core ID assignment logic with `Set`-based conflict tracking
+rather than real-time array scanning. Balanced two requirements:
+
+**Stability**: Preserve IDs across close FEN states (critical for UX)
+**Uniqueness**: Ensure no duplicate IDs ever persist in system
+
+- `ensureUniqueIdsLenient()`: Minimal fixes, preserves stability
+- `ensureUniqueIds()`: Complete reassignment for canonical states
+- `checkForDuplicateIds()`: Detection without modification
+
+Arata moves now maintain hand piece ID stability while giving
+board pieces new IDs, eliminating the duplicate scenario without
+breaking expected behavior.