Codex SessionStart hook fails because hooks.json uses host placeholders in shell command

[cofin]

Summary

The Flow Codex plugin SessionStart hook fails on startup under Codex CLI v0.135.0 because the installed hooks/hooks.json command uses ${extensionPath}${/} placeholders inside a shell command. Codex appears to execute the command through the shell without expanding those placeholders, so Bash treats ${/} as an invalid parameter expansion.

Environment

• Codex CLI: 0.135.0
• Plugin: flow@flow-marketplace version 0.20.5
• Installed manifest: ~/.codex/plugins/cache/flow-marketplace/flow/0.20.5/hooks/hooks.json

Current command

"command": "bun ${extensionPath}${/}hooks${/}session-start.js || node ${extensionPath}${/}hooks${/}session-start.js || bash ${extensionPath}${/}hooks${/}session-start.sh"

Reproduction

Starting Codex in a repo with Flow enabled shows:

SessionStart hook (failed)
error: hook exited with code 1

Running the configured command directly reproduces it:

bash -lc 'bun ${extensionPath}${/}hooks${/}session-start.js || node ${extensionPath}${/}hooks${/}session-start.js || bash ${extensionPath}${/}hooks${/}session-start.sh'
# bash: line 1: ${extensionPath}${/}hooks${/}session-start.js: bad substitution
# exit=1

Calling the script by absolute path succeeds:

node ~/.codex/plugins/cache/flow-marketplace/flow/0.20.5/hooks/session-start.js
# emits hookSpecificOutput.additionalContext JSON and exits 0

Local workaround applied

I patched the installed cache manifest locally to use this command:

"command": "node /home/cody/.codex/plugins/cache/flow-marketplace/flow/0.20.5/hooks/session-start.js || bash /home/cody/.codex/plugins/cache/flow-marketplace/flow/0.20.5/hooks/session-start.sh"

After that, a fresh normal codex exec --json --ephemeral "Respond exactly: OK" completed successfully, and the log rows for that thread had 0 WARN/ERROR/hook failure entries.

Expected fix

Ship a Codex-safe hook manifest for Flow, or update the command template to use whatever plugin-root substitution/environment Codex officially supports. The current ${extensionPath}${/} form is not safe when Codex runs the hook command through Bash.

[cofin]

Fixed in #65 (release 0.21.0). The installed hooks/hooks.json no longer uses ${extensionPath}${/}; the Codex-native manifest now anchors to ${PLUGIN_ROOT:-${CLAUDE_PLUGIN_ROOT:-.}} with the bun || node || bash ladder.

Validated by simulating exactly your repro:

• Installed plugin (cwd outside repo, PLUGIN_ROOT set): runs the package hooks/hooks.json command → emits valid hookSpecificOutput, exit 0. No bad substitution.
• In-repo project layer (.codex/hooks.json, no PLUGIN_ROOT): . fallback + FLOW_HOST=codex → correct payload.

A validate_codex_hook_commands guard + tests now reject any Gemini token or non-$PLUGIN_ROOT path in Codex-consumed manifests, so this can't regress. Will close automatically when #65 merges.