Keeping context and decisions consistent across parallel AI agents

You start the morning with four Claude Code agents running, each in its own git worktree, each on a separate task. By mid-afternoon something is off. One agent has re-implemented a helper another already wrote. A second built against an interface that a third changed an hour ago. A fourth made a naming choice that contradicts a decision you made — out loud, to yourself — at 9am. Every diff is reasonable on its own. The system they add up to is not. This is the failure mode that shows up the moment you go from one agent to several. The code each agent produces is fine. What drifts is everything between the agents: the decisions, the conventions, the current shape of the interfaces they all depend on. Running the agents in parallel is the easy part. Keeping them coherent is the hard part, and it's a different problem. Why parallel agents drift An agent's context is per-session. Each Claude Code instance has its own context window, populated by what it has read and done in that session. Nothing about that window is shared with the agent running in the next worktree. There is no common memory they all write to and read from. So when agent A decides "we use the repository pattern for data access," that decision exists in exactly two places: agent A's context, and your head. Agent B never hears about it. Three kinds of state cause the drift, and they're worth separating because they need different handling: Decisions already made. Architecture, naming, conventions, the approach you settled on for a cross-cutting concern. These are durable — once made, they should bind every agent, including ones you spawn tomorrow. The current contract. The shape of the interfaces, types, and APIs that agents share. This changes during the work: agent A edits a signature, and agents B and C are now building against a version that no longer exists. What's in flight. Who is touching which files right now. Two agents editing the same module in separate worktrees won't see each other until th