Expose session management as tools (rename, list, resume)

Summary

With 1M context, resuming named sessions is becoming a primary workflow — conversations are rich working sessions worth returning to by name. Currently /rename and /resume are interactive-only slash commands. Exposing session management as tools would let the agent manage sessions programmatically.

Proposed tools

1. SessionRename — rename the current session (equivalent to /rename <name>)
2. SessionList — list sessions with optional filters (project, branch, name pattern), returning structured data (name, last activity, message count, branch)
3. SessionResume — resume a specific session by name or ID (may not be feasible mid-conversation, but listing alone would be valuable)

Use cases

• Agent auto-names sessions based on the dominant work topic
• Skills that map tasks/tickets to sessions ("resume work on the auth refactor")
• Session discovery without leaving the current conversation ("which session was I working on the memory architecture in?")
• Building session management workflows in hooks or skills

Current workaround

None — session metadata isn't accessible programmatically. The JSONL files in ~/.claude/projects/ are an internal format with no stability guarantee.