Slack notifications for project uploads

Teams post files to a shared project but only the people who go check the project notice new work. Sharing a link manually in Slack every time is easy to forget.

A project can now be linked to one public Slack channel (Project detail → "…" menu → "Slack notification"; requires the workspace's Slack connection). When a new file is posted to a linked project, the channel gets an automatic message with the title, uploader, and link. Multiple uploads posted in a short window are combined into a single message.

Anyone who doesn't want a specific upload announced can suppress it: check "Don't notify Slack this time" on the web upload screen, pass --no-slack-notify in the CLI, or set slack_notify: false when calling share_artifact via MCP. Version updates to an existing file never trigger a notification — only new posts do. Files shared with specific people only are never announced, regardless of the setting. Notifications are sent in batches every few minutes, so a message can arrive a few minutes after the upload.