Cross-Agent Sessions: Why Claude Code, Cursor, and Codex Don't Share Context

If your team runs more than one AI coding agent — Claude Code for some developers, Cursor for others, Codex in CI — you've probably noticed a specific kind of friction that doesn't show up when everyone uses the same tool: decisions made in one agent's session don't exist for the others.

A developer using Claude Code corrects the agent's pagination approach on Monday. A teammate opens the same codebase in Cursor on Wednesday, working on a related feature, and their agent proposes the exact same rejected approach — because nothing about Monday's correction reached Cursor's session. It's not that Cursor is worse at reasoning. It never had the information.

The four-file workaround, and why it doesn't actually solve this

The standard fix right now is a rules file: CLAUDE.md for Claude Code, AGENTS.md for Codex, .cursor/rules for Cursor, GEMINI.md for Gemini CLI. Maintain one per tool, keep them roughly in sync by hand, and hope nobody forgets to update all four when something changes.

This works, sort of, for a single tool. It doesn't solve cross-agent consistency, for a simple reason: four separate files aren't one shared source of truth — they're four independent copies that drift apart the moment someone updates one and not the others. The Claude Code session and the Cursor session aren't reading the same information; they're reading two different snapshots of it, taken at different times, by different people, with no guarantee they still agree.

And even a single, perfectly maintained rules file has a second problem: it goes stale. You write CLAUDE.md in January. The codebase changes in February. The file doesn't know that — it just keeps confidently teaching every session things that used to be true.

What actually keeping agents in sync requires

Cross-agent consistency isn't a documentation problem, it's a single-source-of-truth problem. It requires:

One store, not one file per tool. A decision captured in any agent should be visible to every agent, immediately — not copy-pasted between four separately-maintained files.

Decisions that update when they change, not files that quietly go stale until someone remembers to edit them.

A human-approval step, so what gets shared across the whole team isn't just whatever one AI session happened to infer — it's what someone actually confirmed is true.

How Contexer handles this

Contexer is built around exactly this problem: a single decision layer that Claude Code, Cursor, Codex, and Gemini CLI all read from and write to. Correct a convention once, in whichever tool you're using at the time, and every future session — in any of the four tools — starts already knowing it. Nothing to copy between files, nothing to keep in sync by hand, because there's only one copy to begin with.

Decisions Contexer captures are held for review before they count as team truth — the agent proposes, a person confirms — so the shared layer stays something your team actually trusts, not just an AI's best guess propagated everywhere at once.

If you're maintaining four rules files right now and watching them drift apart, or if your team's tool choice is starting to fragment across Claude Code and Cursor, this is the specific problem worth solving before it gets worse.