[FEATURE] Hooks Session Start should communicate "forking"

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

I'm developing plugin that helps track threads, and I've had a situation where one of the claude code conversations has crashed and there is now a lock over the transcript causing future claude code sessions that resume to "fork". This is obviously a fine behaviour, however there's no way I can tell this is happening from the hooks on SessionStart, they all appear to be new sessions (but they aren't the transcript in the session shows the old conversation)

Proposed Solution

Add parent_session_id to SessionStart hook.

Alternative Solutions

_No response_

Priority

High - Significant impact on productivity

Feature Category

Developer tools/SDK

Use Case Example

Simply working on https://github.com/wakeless/agent-tracker and ran into this limitation with the data model to enable a "recent agent flow"

Additional Context

_No response_