# Introduce the interface a planned swap needs

The seam a planned replacement needs, added ahead of the replacement with today's implementation behind it.

Category: Architecture and boundaries
Source: https://letsship.ai/use-cases/introduce-the-interface-a-swap-needs
Published: 2026-08-25

## Goal

Introduce the interface a planned swap needs, with the current implementation behind it.

## Acceptance criteria

- Callers depend on the interface rather than the implementation
- A contract test suite pins the behaviour the interface promises
- The current implementation passes that suite unchanged
- No behaviour changes in this ticket

## What lands as proof

A contract suite the current implementation passes, which is what makes the eventual swap a small change.

## Prompt

Copy this to an agent to open the ticket:

```text
Create a Linear issue in my team and assign it to the SHIP agent.

Title: Introduce a {name} interface

Description: Introduce the interface a planned swap needs, with the current implementation behind it.

Acceptance criteria:
- Callers depend on the interface rather than the implementation
- A contract test suite pins the behaviour the interface promises
- The current implementation passes that suite unchanged
- No behaviour changes in this ticket

Before you create the issue, identify a dependency this repository plans to replace and replace {name} with the interface it needs.
```

## Questions

### What does the agent actually change?

The ticket is scoped to one outcome: introduce the interface a planned swap needs, with the current implementation behind it. Work that serves that outcome is in scope, and anything outside it is left for a separate ticket, so the pull request stays reviewable.

### How do I know the work is done?

The pull request carries the evidence, not only the diff. Here that means callers depend on the interface, tests pin the contract, so a reviewer can confirm the result without reproducing the work locally.

### How much oversight does this need?

The run stops once the plan is written. Somebody reads the approach and approves it before any code exists, which is the cheapest moment to redirect the work.