Shared brain
Two AI agents, Claude and Codex, that read the same instructions, keep the same memory and obey the same guardrails. It is the workshop this site was built in.
Since 25 October 2026 · in production, internal use
~/AI · a private git repository
The same rules for both
A single instructions file, read by Claude and by Codex. Fix it once, and both behave differently from their next session.
AGENTS.md - Before an action that is hard to undo, ask for confirmation. - Secrets in .env or a vault, never in code or memory. - Absolute dates, never “yesterday”.
One fact per file
Every pitfall, decision or project state becomes a dated note, signed by the agent that wrote it, indexed and pushed to git. The other agent reads it at the start of its task.
--- name: project-quintiro type: project updated: 2026-11-02 by: claude --- Pitfall: nginx does not know .mjs and serves the PDF.js worker as octet-stream; the browser refuses to run it. Fixed in deploy/nginx.conf.
Reusable procedures
A procedure that works becomes a shared skill: for instance, setting up SEO tracking for a new site. Both agents follow it step by step.
skills/seo-second-brain/SKILL.md Use when creating any new website: SEO map, rules, decision log, guardrails.
One list, two installs
Connectors (Search Console, browser…) are described once; a script installs them in both tools.
mcp/servers.json → sync.py ✓ installed in Claude Code ✓ installed in Codex
Rules that run
Some rules are not up for discussion: a hook blocks any change to a protected file, whichever agent tries. Tested on both.
$ edit robots.txt ✗ blocked: protected file (seo/protected.txt) only a human edits it.
The challenge
Every session starts from scratch, and every tool keeps its own memory in its own corner. Across ten projects run in parallel, the same decisions get explained again and again, and a pitfall found by one is found again, later, by the other.
The approach
- A single source: both tools read the same instructions file, through a symbolic link.
- A memory made of notes, one fact per file, dated and signed by the agent that wrote it, versioned in git.
- Guardrails that run, not just written down: a protected file is blocked for both agents.
The numbers
- 1 day for quintiro.com: brand, foundation, three tools and launch
- 220 versions of the shared memory
- 18 memory notes, one per fact
- 2 agents from two different vendors, tied to neither
Counted on 2 November 2026 in the git repository of the shared memory and in the history of quintiro.com.
- Claude Code
- Codex
- git
- Markdown
- MCP
- Hooks
Updated 2 November 2026