[FEATURE] Allow shared sessions to be resumed by another user via `claude --resume`

Problem Statement

Today, two collaboration features exist independently but don't connect:

• Session sharing — you can share a session via link or /export
• claude --resume — you can resume a previous session locally

But there is no bridge between them. A session shared with a teammate cannot be resumed in their CLI. The session is read-only at best, and the recipient has no way to interact with it — including approving or rejecting a pending /plan.

Proposed Solution

Extend claude --resume to accept a shared session identifier (the same token used for session sharing), so a teammate can resume a session in their own CLI with full interactivity — including plan approval.

Optional access controls to consider:

• Read-only vs. interactive resume modes
• Expiring share tokens
• Approval-only mode (teammate can only approve/reject a pending plan, not issue new prompts)

Alternative Solutions

Manually copy the plan text, share via Slack/email, get approval out-of-band, then execute in the original session. Clunky and breaks the flow.

Priority

Low - Nice to have

Feature Category

CLI commands and flags

Use Case Example

I generate a plan in plan mode (/plan) and want a teammate to review it and either approve or reject it before any code is changed. Today this requires copying the plan text manually and communicating out-of-band. The teammate cannot act on the plan inside Claude Code — they can only read it.

If shared sessions were resumable, the workflow would be:

1. Developer A runs /plan, gets a pending plan
2. Developer A shares the session link
3. Developer B runs claude --resume <shared-session-id> in their own terminal
4. Developer B sees the pending plan and approves or rejects it
5. Execution (or cancellation) proceeds from there

Additional Context

Why This Matters

This unlocks a natural human-in-the-loop review flow for teams: one developer drives, another reviews and approves before anything is written to disk. It complements plan mode's safety guarantees and makes Claude Code genuinely collaborative at the CLI level, not just via the web UI.