Agent Teams: adopt existing sessions into a team after the fact

Summary

Agent Teams (CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=1) currently requires teammates to be spawned by the lead from the start. There's no way to pull two (or more) already-running, independent Claude Code sessions into a team after the fact.

Motivation

The need for cross-session collaboration often isn't predictable at session start. A common pattern:

• Session A has spent an hour accumulating deep context on subsystem X
• Session B has done the same on subsystem Y
• Mid-work, it becomes clear they should reconcile a design decision

Today the only options are (a) lossy hand-off via exported briefs, or (b) third-party bridges like PatilShreyas/claude-code-session-bridge (1:1) and yakub268/claude-multi-agent-bridge (N-way HTTP hub). That community demand suggests a real gap.

Request

A way to "join" or "adopt" a running session into a team — e.g., /team join <id> from one side and /team invite <id> from the lead — so each participant keeps its accumulated context window and gains access to the existing mailbox/task-list primitives.

Nice-to-haves

• N>2 participants
• Works whether the joiner started as a standalone session or was previously part of another team