feat: add self-terminate plugin for graceful session exit

Adds a plugin that enables Claude to terminate its own session by
sending SIGINT to its process. Includes:
- Executable script (bin/self-terminate.sh)
- Skill documentation explaining manual and automated methods
- Safety verification to ensure parent is actually Claude

Co-Authored-By: Claude Code (~/.ai.worktrees/subagent-via-tmux) <noreply@anthropic.com>

Author: nsheaps

plugins/self-terminate/.claude-plugin/plugin.json

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+{
+  "name": "self-terminate",
+  "version": "1.0.0",
+  "description": "Allows Claude to gracefully terminate itself using SIGINT",
+  "author": {
+    "name": "Nathan Heaps",
+    "email": "nsheaps@gmail.com",
+    "url": "https://github.com/nsheaps"
+  },
+  "homepage": "https://github.com/nsheaps/.ai/tree/main/plugins/self-terminate",
+  "repository": "https://github.com/nsheaps/.ai",
+  "keywords": ["terminate", "exit", "sigint", "process", "self-destruct"]
+}

plugins/self-terminate/README.md

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+# Self-Terminate Plugin
+
+A Claude Code plugin that enables Claude to gracefully terminate its own session.
+
+## Installation
+
+This plugin is part of the nsheaps/.ai plugin collection. Install via:
+
+```bash
+claude plugins install github:nsheaps/.ai/plugins/self-terminate
+```
+
+## Usage
+
+### Via Script (Recommended)
+
+Claude can simply execute the provided script:
+
+```bash
+~/.claude/plugins/self-terminate/bin/self-terminate.sh
+```
+
+### Via Skill
+
+The skill provides detailed instructions for manual termination if needed.
+
+## How It Works
+
+Claude Code runs as a process that spawns subshells for Bash commands. The script:
+
+1. Identifies the parent process (Claude) via `$PPID`
+2. Verifies it's actually a Claude process
+3. Sends `SIGINT` for graceful termination
+
+## Why SIGINT?
+
+- **SIGINT (2)**: Graceful interrupt, allows cleanup
+- **SIGTERM (15)**: Also graceful, but SIGINT is more conventional for user-initiated stops
+- **SIGKILL (9)**: Force kill, no cleanup - avoid unless necessary
+
+## Files
+
+- `bin/self-terminate.sh` - Executable script for termination
+- `skills/self-terminate/SKILL.md` - Detailed skill documentation
+
+## License
+
+MIT

plugins/self-terminate/bin/self-terminate.sh

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+#!/usr/bin/env bash
+# Self-terminate script for Claude Code
+# Sends SIGINT to the Claude process that spawned this shell
+
+set -euo pipefail
+
+# Get the parent PID (Claude process)
+CLAUDE_PID="$PPID"
+
+# Verify it's actually a claude process
+PROCESS_NAME=$(ps -o comm= -p "$CLAUDE_PID" 2>/dev/null || echo "unknown")
+
+if [[ "$PROCESS_NAME" != *"claude"* ]]; then
+    echo "Error: Parent process ($CLAUDE_PID) is not Claude (found: $PROCESS_NAME)" >&2
+    exit 1
+fi
+
+echo "Sending SIGINT to Claude process (PID: $CLAUDE_PID)..."
+kill -INT "$CLAUDE_PID"

plugins/self-terminate/skills/self-terminate/SKILL.md

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+---
+name: self-terminate
+description: Gracefully terminate the Claude Code session by sending SIGINT to the Claude process
+---
+
+# Self-Terminate Skill
+
+This skill enables Claude to gracefully terminate its own session by sending a SIGINT signal to its process.
+
+## When to Use This Skill
+
+- When the user explicitly asks Claude to exit or terminate
+- When Claude needs to restart with a fresh session
+- When testing process management or signal handling
+
+## How It Works
+
+Claude runs as a process that spawns shell subprocesses for Bash commands. The parent PID (`$PPID`) of any spawned shell is the Claude process itself.
+
+Sending `SIGINT` (signal 2) to the Claude process triggers a graceful shutdown, similar to pressing `Ctrl+C`.
+
+## Quick Method: Use the Script
+
+The easiest way is to execute the provided script:
+
+```bash
+/path/to/plugins/self-terminate/bin/self-terminate.sh
+```
+
+Or if the plugin is installed:
+
+```bash
+~/.claude/plugins/self-terminate/bin/self-terminate.sh
+```
+
+## Manual Method
+
+If the script is unavailable, Claude can terminate itself manually:
+
+### Step 1: Identify the Claude Process
+
+```bash
+echo "Shell PID: $$"
+echo "Claude PID (parent): $PPID"
+ps -o pid,ppid,comm -p $$ -p $PPID
+```
+
+### Step 2: Verify It's Claude
+
+```bash
+ps -o comm= -p $PPID
+```
+
+This should output `claude` or similar.
+
+### Step 3: Send SIGINT
+
+```bash
+kill -INT $PPID
+```
+
+## Process Tree Context
+
+A typical Claude Code process tree looks like:
+
+```
+iTerm/Terminal
+└── shell (user's interactive shell)
+    └── claude (PID: XXXXX)  ← Target this
+        └── /bin/zsh (spawned for Bash commands)
+            └── (your command)
+```
+
+## Safety Notes
+
+- **SIGINT** causes graceful termination - Claude can clean up
+- **SIGTERM** also works for graceful shutdown
+- **SIGKILL** (-9) should be avoided - no cleanup opportunity
+- The script verifies the parent is actually Claude before sending the signal
+
+## What Happens After
+
+After termination:
+1. The Claude session ends immediately
+2. Any in-progress work is interrupted
+3. The user returns to their shell
+4. A new session can be started with `claude`
+
+## Troubleshooting
+
+**Script says parent is not Claude**: You may be running in a nested shell or different environment. Check `pstree -p $$` to see the full process tree.
+
+**Signal ignored**: Some environments may mask signals. Try `kill -TERM $PPID` as an alternative.