Feature request: Canonical trigger phrase or slash command for agents to self-report resume command

Summary

Related to #52262 (agents cannot self-report their resume command). Even once the session ID is retrievable, there is no canonical way for a user to ask "what is the full command to resume this session?" and get a reliable, consistent answer.

Current behavior

Asking three different agents the same question gets three different (mostly wrong) answers:

• Agent 1: "--resume does not exist, you have to start a new session"
• Agent 2: "Just run claude in the project directory, the compact recovery handles it"
• Agent 3 (after being corrected): Finally gives the correct command

The variation is a UX failure. Users have no reliable phrase or command that will consistently work across all agents.

Requested behavior

Either:

• A canonical slash command like /resume-command that prints the exact reattach command for the current session
• A documented magic phrase that all agents are trained to respond to consistently
• An environment variable CLAUDE_SESSION_ID + a documented template users can rely on

Why this matters

Multi-agent workflows (1 PM + 6-8 workers) require users to reattach specific sessions every time they log out, switch terminals, upgrade CLI, or recover from a crash. Without a reliable self-report mechanism, users waste time asking, getting wrong answers, and manually hunting JSONL files.

Related: #52262, #37442.