[BUG] SessionStart hook stdout is silently dropped when source=clear

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?

This problem has appeared while trying to create a hook for /clear that will list the latest projects being worked on (just modification timestamp of some folders). The hook works perfectly on new session, can't work on /clear due to TTY limitations: the list of projects is passed to the model as context but can't be written to the terminal. I was trying to work around it by giving the model a prompt to output that project list it already has in the context, but it doesn't work until a first promt is made on the new post-/clear session. Hook debug log attached

• Evidence: Hook fires (confirmed via debug log), produces stdout, but Claude Code shows "(no content)" — the output is neither shown to the user nor added as model context
• Expected: stdout should be added as model context, matching startup and resume behavior
• Workaround: None currently — /dev/tty doesn't work post-TUI, and stdout is dropped

hook-debug.log

What Should Happen?

Model should follow the prompt

Error Messages/Logs

Steps to Reproduce

Attaching hook invoked by this config

recent-projects.sh

"outputStyle": "Explanatory",
"hooks": {
"SessionStart": [
{
"hooks": [
{
"type": "command",
"command": "\"$CLAUDE_PROJECT_DIR\"/scripts/recent-projects.sh"
}
]
}
]

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.41 (Claude Code)

Platform

Google Vertex AI

Operating System

Other Linux

Terminal/Shell

Other

Additional Information

_No response_