[FEATURE] track cost on multiple sessions and provide a shutdown hook to do that ?

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

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Title: Add SessionEnd hook and expose /cost data to hooks

Body:

Feature Request

Problem

There's no way to run automation when a Claude Code session ends, and /cost data (session cost, tokens, duration) is only available as an internal CLI command — not exposed to hooks or scripts.

Requested Features

1. SessionEnd hook event — fires once when the session exits (via /exit, Ctrl+C, or terminal close). This would enable cleanup tasks, cost tracking, session logging, etc.
2. Expose /cost data to hooks/environment — make session cost/token data available as:

• Environment variables ($CLAUDE_SESSION_COST, $CLAUDE_SESSION_TOKENS_IN, etc.), or
• A JSON file written on session end (~/.claude/last-session-cost.json)

Proposed Solution

Automatic cost tracking across sessions. Currently the only workflow is manually running /cost and copying numbers. With these two features, a plugin could automatically append cost data to a tracking file
on every session exit.

Alternative Solutions

Workaround

Currently using a /update-cost slash command that requires the user to manually run /cost first, then /update-cost to parse the output from conversation context.

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

Workaround

Currently using a /update-cost slash command that requires the user to manually run /cost first, then /update-cost to parse the output from conversation context.

Additional Context

_No response_