[FEATURE] Add SessionExit hook event (e.g., for cost tracking)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

There's no way to run cleanup commands when a Claude Code session ends. The current hook events (PreToolCall, PostToolCall, Notification, Stop) don't cover session termination via /exit, Ctrl+C, or natural completion.

Proposed Solution

Add a SessionExit hook event that fires when:

• User types /exit
• User presses Ctrl+C
• Session ends naturally

Example configuration in settings.json:

  {
    "hooks": {
      "SessionExit": [{
        "command": "~/.claude/scripts/log-session-cost.sh"
      }]
    }
  }

Alternative Solutions

• Shell wrapper: Wrapping the claude command in a shell function works but feels hacky and doesn't capture Ctrl+C gracefully
• PostToolCall hook: Logging on every tool call is wasteful and creates duplicate entries

Priority

Medium - Would be very helpful

Feature Category

Other

Use Case Example

I want to automatically log session costs (token usage, API costs) to a CSV file when exiting Claude Code. Currently I have to manually invoke a custom slash command before every exit, which is easy to forget.

Additional Context

_No response_