already have location bindings (on_shelf or transferred)
- Replace single on_shelf pre-check with unified conflict detection
for both normal shelf and transit targets
- Show conflict dialog listing duplicate and/or transferred items
with details before any API calls are made
- Prevents partial batch failures where some items succeed before
a conflicting item is encountered
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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