Web UI: paperclip button for file upload (images, PDFs, text), inline
attachment cards with file icon/name/size, image thumbnails with
fullscreen overlay, attachment display in thread panel.
Threads: always-visible reply count badges on messages, clickable to
open thread panel. reply_count and attachments enriched in all API
responses via batch queries.
MCP: attachments parameter on send_message tool, updated tool
descriptions for threading and attachment workflow guidance.
Backend: file type validation (allowlist), AttachmentLinker interface
to avoid circular deps, GetReplyCounts batch query, EnrichMessages
method on MessagingService.
Admin CLI: synapbus attachments backup/restore with tar.gz archives,
dedup-safe restore.
24 new test cases across 4 packages. All 24 test packages pass.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
