Use plan.md to Coordinate Work Across Parallel Claude Sessions

Running multiple Claude sessions in parallel is powerful, but without coordination they can duplicate work, conflict on files, or undo each other's changes. A shared plan.md in the project root solves this.

Each session reads the plan before acting, and updates it before handing off:

# Feature: Checkout Flow

## In Progress
- Session A: payment form validation (src/components/PaymentForm.vue)
- Session B: writing tests for OrderService (tests/Feature/OrderTest.php)

## Completed
- [x] Cart summary component
- [x] Address form with validation

## Blocked
- Email receipt — waiting on SMTP credentials

## Decisions
- Using Stripe Elements for card input (no raw card data on our server)
- Skipping PayPal for v1

Before starting work, each Claude session reads the plan:

Read plan.md. I'm Session B. What's left for me to work on that doesn't 
conflict with what's in progress?

After completing a step, the session updates the plan:

Mark "writing tests for OrderService" as complete in plan.md and 
note any constraints the next session should know about.

The plan.md acts as the shared memory that all sessions — and all future context windows — can rely on. Unlike chat history, it persists on disk and is readable by any session at any time.

With a shared plan.md, parallel sessions become a coordinated team rather than independent workers who don't know what the others are doing.

via @ShaneCollinsAI