- New migration 004: memory_shares and tag_shares tables with indexes
- Share individual memories or entire tags with other users (read/write)
- Tag shares are live rules: future memories with shared tags auto-visible
- Recall query merges own + shared memories via UNION, returns shared_by field
- Owner-only delete enforcement (403 for non-owners, even with write access)
- PUT /api/memories/{id} update endpoint with permission checks
- 5 new MCP SSE tools: memory_share, memory_unshare, memory_share_tag,
memory_unshare_tag, memory_update
- Permission helper checks ownership, individual shares, and tag shares
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