[BUG] SessionStart hook not injecting prompt at conversation start

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Title: SessionStart hook not injecting prompt at conversation start

Description:

The SessionStart hook configured in settings.json is not firing or not injecting its prompt into the conversation context when a new session begins.

Expected behavior:
When a session starts, the prompt defined in SessionStart hook should be automatically injected so Claude has that context from message one.

Actual behavior:
The hook either doesn't fire or the prompt isn't injected. Claude doesn't have the configured context until explicitly reading settings.json.

Configuration:
"hooks": {
"SessionStart": [
{
"hooks": [
{
"type": "prompt",
"prompt": "Your name is Claude and my name is Frank. Your answers will be concise, honest, and objectively brutal if necessary because I value honesty and useful feedback. Begin."
}
]
}
]
}

Impact:
Mission critical - defeats the purpose of having SessionStart hooks if the assistant doesn't receive configured context automatically.

Environment:

• OS: macOS (Darwin 24.6.0)
• Claude Code version: 0.0.120

What Should Happen?

Expected behavior:
When a session starts, the prompt defined in SessionStart hook should be automatically injected so Claude has that context from message one.

Error Messages/Logs

Steps to Reproduce

start new session, watch everything get ignored

Claude Model

None

Is this a regression?

I don't know

Last Working Version

Claude Code version: 0.0.120

Claude Code Version

Claude Code version: 0.0.120

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_