test(NODE-7470): test that backpressure retries are non-blocking

[dariakp]

Description

NODE-7470

Summary of Changes

Sync client backpressure tests to latest

Fixed bug that appears on LB topologies: unpin sessions on SystemOverloadedError during retries so that connections are checked back into the pool during the backoff period, rather than being held for the entire retry sequence. This was already handled for MongoNetworkError but not for server-side overload errors, which caused the connection to remain pinned in load-balanced mode across all retry attempts.

Notes for Reviewers

N/A

Double check the following

• Lint is passing (npm run check:lint)
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[Copilot]

Pull request overview

This PR updates the client backpressure retry behavior and adds a unified spec test to ensure connections are returned to the pool between retry attempts when the server reports overload (particularly relevant for load-balanced topologies where sessions can pin connections).

Changes:

• Added a new unified spec test asserting connectionCheckedOut/connectionCheckedIn pairing across overload retry attempts.
• Updated the retry loop to unpin pinned sessions when retrying SystemOverloadedError so connections can be checked back into the pool.
• Added generated JSON alongside the YAML spec.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
test/spec/client-backpressure/backpressure-connection-checkin.yml	New unified spec asserting connections are checked back in during overload retries.
test/spec/client-backpressure/backpressure-connection-checkin.json	Generated JSON version of the new unified spec.
src/operations/execute_operation.ts	Adds session unpinning logic on SystemOverloadedError within the retry loop.

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[Copilot]

Pull request overview

This PR updates the Node driver’s client backpressure coverage and fixes a load-balanced (LB) retry behavior where cursor-creating operations could keep a session’s pinned connection checked out across SystemOverloadedError retries, instead of returning it to the pool during backoff.

Changes:

• Add a new unified test that asserts connections are checked back into the pool between overload retry attempts.
• Update retry logic to unpin LB sessions on SystemOverloadedError for cursor-creating operations (mirroring existing unpin behavior for MongoNetworkError).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
test/spec/client-backpressure/backpressure-connection-checkin.yml	Adds unified YAML test asserting per-attempt CMAP check-out/check-in for overload retries.
test/spec/client-backpressure/backpressure-connection-checkin.json	JSON equivalent of the new unified test for overload retry connection check-in behavior.
src/operations/execute_operation.ts	Unpins pinned LB sessions on SystemOverloadedError during retry loop so connections return to the pool during backoff.

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[PavelSafronov]

Looks good!