Add stash plugin: multi-slot message storage with push/pop/apply/list

[leonardocardoso]

Summary

Adds a new plugin that provides git-stash-like message storage for Claude Code, addressing the limitations of the built-in Ctrl+S single-slot stash.

Fixes #26615
Related: #24776, #20068 (provides a workaround — messages persist to disk)

Motivation

The built-in Ctrl+S stash has three limitations reported across multiple issues (#26615, #24776, #20068, #20806):

• Single slot — stashing again overwrites the previous stash
• Not persisted to disk — lost on crashes, errors, or session changes
• No history — no way to browse or select from multiple stashes

This plugin provides a proper stack persisted to ~/.claude/stash.jsonl.

Commands

Command	Description
/stash <message>	Push a message to the stash stack
/stash-pop	Apply and remove the last stashed message
/stash-apply <id>	Apply and remove a specific stash by ID
/stash-list	List all stashed messages

Implementation

• Storage: JSONL file at ~/.claude/stash.jsonl (one JSON object per line)
• Runtime: Python 3 (pre-installed on macOS/Linux, consistent with hookify and security-guidance plugins)
• Each command runs a single python3 -c invocation for atomicity

Testing

Tested all commands end-to-end:

• Stash multiple messages, verify sequential IDs
• List with truncation for long messages
• Apply by ID, verify removal from stack
• Pop last entry, verify removal
• Edge cases: empty stash, non-existent ID, pop until empty