Skip replayed letter event

[stevebux]

Description

Context

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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Sensitive Information Declaration

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• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.

[Copilot]

Pull request overview

This PR aims to make the upsert-letter flow idempotent by treating replayed “insert” events (where the letter already exists) as non-failures, and updating tests/utilities accordingly.

Changes:

• Introduce and propagate a LetterAlreadyExistsError from the datastore, and handle it in the upsert-letter Lambda by logging a warning instead of failing the batch item.
• Refactor CloudWatch polling test helpers and update component tests to look for a warning (rather than an error) for duplicate/replayed events.
• Update event schema dependency version in package-lock.json.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/helpers/aws-cloudwatch-helper.ts	Refactors log polling into a generic helper and adds warning polling for upsert-letter logs.
tests/constants/api-constants.ts	Alters how the test environment name is determined for AWS resource naming.
tests/component-tests/letterQueue-tests/queue-operations.spec.ts	Updates duplicate insert assertion to poll for a warning log.
tests/component-tests/events-tests/event-subscription.spec.ts	Updates duplicate event assertion to poll for a warning log.
package-lock.json	Bumps @nhsdigital/nhs-notify-event-schemas-supplier-api version.
lambdas/upsert-letter/src/handler/upsert-handler.ts	Catches LetterAlreadyExistsError and logs a warning instead of failing.
lambdas/upsert-letter/src/handler/tests/upsert-handler.test.ts	Adds unit test ensuring replayed insert does not create batch failures; updates logger mock to include warn.
lambdas/upsert-letter/jest.config.ts	Adds transformIgnorePatterns exception for event schema package(s).
internal/datastore/src/letter-repository.ts	Throws LetterAlreadyExistsError on conditional put conflict.
internal/datastore/src/test/letter-repository.test.ts	Updates expectation to assert LetterAlreadyExistsError is thrown.