[DOCS] Hooks reference omits the SessionStart “fork” source

Documentation Type

Missing documentation (feature not documented)

Documentation Location

https://code.claude.com/docs/en/hooks

Section/Topic

The SessionStart matcher table and SessionStart input schema.

Current Documentation

The SessionStart section currently lists these matcher values:

startup — New session resume — --resume, --continue, or /resume clear — /clear compact — Auto or manual compaction

It describes the source field as:

How the session started: “startup” for new sessions, “resume” for resumed sessions, “clear” after /clear, or “compact” after compaction

What's Wrong or Missing?

Claude Code 2.1.214 changes forked sessions so SessionStart hooks report source “fork” rather than “resume”. The matcher table and input schema enumerate the older values and do not explain how a hook should distinguish a fork from a normal resume.

A hook that refreshes context, sets environment variables, or applies different initialization for resumed sessions can now misclassify a forked session and perform the wrong work.

Suggested Improvement

Add fork to both the matcher-value table and the source field description. Explain that it is emitted when a session begins as a fork, and include a JSON input example such as:

~~~json
{
"hook_event_name": "SessionStart",
"source": "fork"
}
~~~

Add a short guidance note explaining when to treat fork like startup, resume, or a separate initialization path, and add a 2.1.214 minimum-version marker.

Impact

Medium - Makes feature difficult to understand

Additional Context

Affected Pages:

| Page | Context |
|------|---------|
| https://code.claude.com/docs/en/hooks | SessionStart matcher values and input schema |
| https://code.claude.com/docs/en/hooks-guide | Hook setup and lifecycle cross-reference |

Release: Claude Code 2.1.214.