perf: replace Node.js SessionStart hook with bash (106ms → 5ms)

[KRRT7]

Summary

• Replace the Node.js SessionStart hook with an equivalent bash script
• SessionEnd stays in Node.js (requires async broker teardown and process tree management)

Why

The SessionStart handler in session-lifecycle-hook.mjs only appends two env vars (CODEX_COMPANION_SESSION_ID and CLAUDE_PLUGIN_DATA) to CLAUDE_ENV_FILE. Running this through Node.js pays ~100ms of V8 startup overhead on every session start for what amounts to two file appends.

Bare Node.js startup on this machine:

$ hyperfine --warmup 5 --runs 30 'node -e "1"'
Time (mean ± σ):  98.3 ms ± 7.4 ms

The actual work (appendEnvVar × 2) adds <10ms on top. A bash script doing the same shell-escaped writes avoids V8 entirely.

Changes

1. scripts/session-start-env.sh (new): Reads session_id from hook JSON input via jq, appends shell-escaped export lines to $CLAUDE_ENV_FILE. Exact same escaping logic as the Node.js shellEscape() function.
2. hooks/hooks.json: SessionStart entry points to the new bash script instead of session-lifecycle-hook.mjs.

Benchmark

macOS, Apple Silicon (M4 Max), 30 runs, 5 warmup via hyperfine:

Hook	Before (Node.js)	After (bash)	Delta	Speedup
SessionStart	106 ms	5 ms	██████████ -95%	21.2x

Reproduce with hyperfine

Requires hyperfine and jq.

# Create test input
printf '{"session_id":"test-123"}\n' > /tmp/session-input.json

# Measure Node.js version (current main)
CLAUDE_ENV_FILE=/tmp/test-env \
  hyperfine --warmup 5 --runs 30 \
  --prepare 'rm -f /tmp/test-env' \
  'node plugins/codex/scripts/session-lifecycle-hook.mjs SessionStart < /tmp/session-input.json'

# Measure bash version (this branch)
CLAUDE_ENV_FILE=/tmp/test-env \
  hyperfine --warmup 5 --runs 30 \
  --prepare 'rm -f /tmp/test-env' \
  'bash plugins/codex/scripts/session-start-env.sh < /tmp/session-input.json'

Test plan

• Output matches Node.js version: same export lines with identical shell escaping
• CODEX_COMPANION_SESSION_ID set correctly in session after start
• CLAUDE_PLUGIN_DATA set correctly in session after start
• Empty/missing CLAUDE_ENV_FILE exits cleanly (exit 0, no error)
• Shell escaping handles single quotes in values
• SessionEnd still routes to Node.js and tears down broker correctly

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: bce5e90940

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• Mark a draft as ready
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[chatgpt-codex-connector]

Avoid requiring jq in SessionStart hook

This change introduces a hard runtime dependency on jq for every SessionStart via SESSION_ID=$(... | jq ...); with set -euo pipefail, systems lacking jq now fail the hook with exit 127 before writing CODEX_COMPANION_SESSION_ID/CLAUDE_PLUGIN_DATA. The previous Node.js path did not require jq, and the repo requirements only document Node, so this is a real compatibility regression that can break plugin startup on otherwise supported environments.

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