The pack only helps a Grok session if it reaches the model.

Grok discards UserPromptSubmit stdout. It delivers PostToolUse additionalContext after the first tool. ljos hook searches on the prompt, holds the text, and emits it once on PostToolUse. PreToolUse is rules only. There is no sync.sh.

Install

$ ljos onboard --harness grok

That writes ~/.grok/hooks/ljos.json once (ljos hook on PATH). Then /hooks then r once. Later cargo binstall ljos is live on the next event. Name ljos-mcp on PATH in ~/.grok/config.toml. Bump LJOS_MCP_GENERATION in that table when you want Grok’s config watcher to respawn the server.

Why these events

Event	What ljos hook does	What Grok does with stdout
UserPromptSubmit	searches, holds the text	discarded
PostToolUse	emits the held text once	delivered after the tool
PreToolUse	rules only	a turn has many tool calls
SessionEnd	fires injected memories	ignored

The frozen file is scripts/grok/ljos.json. It only names ljos hook.

Smoke

$ echo '{"hook_event_name":"PreToolUse","tool_input":{"command":"echo"}}' | ljos hook
$ echo '{"hook_event_name":"PostToolUse","session_id":"s"}' | ljos hook

A tool call prints nothing unless a prompt has already held pack text.

harnesses.toml

[[harness]]
name = "grok"
config = "~/.grok/config.toml"
marker = "[mcp_servers.ljos]"
skills = "~/.config/ljos/skills"
hooks = "~/.grok/hooks/ljos.json"
hook_events = ["UserPromptSubmit", "PostToolUse", "PreToolUse", "SessionEnd"]