Keep the thread on what your AI agent shipped. This Codex plugin bundles, in one install:

• the backthread MCP server (the query "how does X work?" tool + capture), and
• an automatic Stop capture hook — every session's decisions (the why) are captured when a turn ends, with no manual step.

Your source code and tool I/O never leave your machine — Backthread redacts every transcript locally before anything is sent. See backthread.dev/security.

Both the MCP server and the hook run the published backthread CLI via npx, so the plugin itself is just config — nothing to build.

# Register this directory as a Codex plugin marketplace, then install via /plugins:
codex plugin marketplace add ./extensions/codex
# then, inside Codex:  /plugins  → install "backthread"

One-time sign-in (authorizes this device; the token is never printed):

npx backthread login

That's it. Ask "how does X work?" and Codex will use the query tool; keep coding and each session is captured automatically.

• plugins/backthread/.mcp.json → the backthread MCP server (npx -y backthread mcp).
• plugins/backthread/hooks/hooks.json → a Stop hook running npx -y backthread@latest capture --from-hook --agent codex --detach. Codex's Stop fires at turn scope and is awaited (it expects a JSON ack on stdout), so the capture detaches a worker — it prints the { "continue": true } ack and returns instantly so it never adds latency to a turn, while the redact → derive → persist round-trip finishes in the background. The shared --from-hook entrypoint dedupes per session, so the per-turn Stop captures each session only once.

Built against the official Codex plugin + hooks docs, but confirm on a real Codex install before relying on it:

• .mcp.json direct server map (vs a wrapped { "mcpServers": … } object) — the docs call the direct map standard; verify the server loads.
• marketplace.json source: { source: "local", path } shape + whether codex plugin marketplace add <dir> discovers marketplace.json at the dir root.
• Stop ack — Codex expects JSON on stdout when the hook exits 0; the --agent codex path emits { "continue": true, … }. Confirm the turn isn't blocked.

The verified two-file fallback (write ~/.codex/config.toml MCP + [[hooks.Stop]]) is backthread install --agent codex (ARP-503).

• Node.js ≥ 22.18 (for npx backthread)
• Codex CLI ≥ 0.124.0 (hooks stable) / ≥ 0.117.0 (plugins)

• backthread.dev · How your data is handled
• The backthread CLI: npm · source