[FEATURE] Show session/agent IDs in --resume interactive picker

Problem Statement

When using claude --resume to interactively select a previous session, the picker only shows session summaries. This makes it difficult to:

• Track and navigate between branched/forked conversations
• Identify which session branch you're resuming
• Distinguish between multiple sessions with similar summaries
• Keep mental context when working with multiple conversation branches on the same topic

When you fork a conversation or resume with automatic branching, the new session gets a different ID, but there's no way to see this in the picker, making it hard to manage branched conversation trees.

Proposed Solution

Update the --resume interactive picker to display session/agent IDs alongside summaries:

\\\
? Select a conversation to resume:
[83b42dcf-5b20] OpenPhone SMS Data Extraction Component Fixed
[agent-945203d6] Claude Code CLI Overview (agent session)
[64e66d06-d282] Database migration implementation
\\\

Key improvements:

• Show shortened session ID (first 12 characters of UUID)
• Prefix agent sessions with "agent-" and their short ID
• Include "(agent session)" indicator for clarity
• Keep session summaries as the primary description

Alternative Solutions

1. Add a --list-sessions flag that outputs all session IDs with summaries
2. Include session ID in the status bar during resumed sessions
3. Add a /session-info command to show current session metadata
4. Show a tree view of branched conversations

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

1. I'm working on a feature and create multiple conversation branches to explore different approaches
2. Each time I resume with --resume, Claude Code creates a new session ID (automatic branching)
3. Later, I want to go back to a specific branch to continue that exploration path
4. Currently, I can only see summaries which might be identical or very similar across branches
5. With session IDs visible, I could identify exactly which conversation branch I want to resume
6. This helps me manage my exploration workflow when trying multiple approaches to the same problem

Additional Context

• Session files are stored as: \~/.claude/projects/<encoded-dir>/<uuid>.jsonl\
• Agent sessions use format: \agent-<short-id>.jsonl\
• The session ID is already available (it's the filename) - just needs to be displayed in the UI
• When resuming, Claude Code automatically creates new session IDs to preserve conversation history