Feature request: expose Slack's Later list (saved + reminders + follow-ups) via MCP tools, with status-change support

Feature request: expose Slack's "Later" list via new MCP tools (read + write)

Slack's Later view bundles three sources into a single stateful
follow-up list with tabs for In progress / Archived / Completed:

• Saved/bookmarked messages
• Slackbot reminders
• DMs and threads marked "follow up"

The MCP currently surfaces only the saved/bookmarked subset via the
is:saved search modifier. Missing on the read side:

• Reminders (reminders.list in the Web API)
• DMs/threads marked "follow up"
• Per-item state (In progress / Archived / Completed)

And there's no write-side capability: an agent can read what's saved
but can't mark items Archived or Completed.

An agent trying to answer "what's still open for me?" has to approximate
by walking recent DMs and saved items separately, which misses reminders
entirely and can't tell which items the user has already marked Completed.
Without a status-change tool, an agent that just helped you resolve an
item also can't close it out — the user has to context-switch back to
Slack to flip the state manually.

Proposed shape

Two tools — one read, one write:

slack_list_later_items:

• Inputs: tab (in_progress | archived | completed; default in_progress),
  optional limit, optional cursor.
• Output per item: stable item id, source type (saved | reminder | follow_up),
  original channel/thread/DM context, message preview, created_at,
  state, and a Slack permalink.

slack_set_later_item_status:

• Inputs: item_id (from list), state (in_progress | archived | completed).
• Behaves like the corresponding tab toggle in the Slack UI.

Start by tracing the existing is:saved search path and the Slack Web API reminders.list entry point. Define how saved items, reminders, and follow-ups map to stable IDs and tabs, then implement the two proposed MCP tools; done means listing the requested state and changing an item's state as described.