fix(#10298): update device_by_user to use built-in reduce [DO NOT MERGE]

[dianabarsan]

Description

Updates device_by_user reduce function to be built-in _last.

Performance results, querying database with 400.000 telemetry documents:

branch	time	improvement
master	1144s
proposed	33s	34 times faster

Unfortunately, the new built-in reduce _last was added in CouchDb 3.5, which means that upgrades from older versions of CHT, that use CouchDb 3.4 will fail.

closes #10298

Code review checklist

• UI/UX backwards compatible: Test it works for the new design (enabled by default). And test it works in the old design, enable can_view_old_navigation permission to see the old design. Test it has appropriate design for RTL languages.
• Readable: Concise, well named, follows the style guide, documented if necessary.
• Documented: Configuration and user documentation on cht-docs
• Tested: Unit and/or e2e where appropriate
• Internationalised: All user facing text
• Backwards compatible: Works with existing data and configuration or includes a migration. Any breaking changes documented in the release notes.

Compose URLs

If Build CI hasn't passed, these may 404:

• Core
• CouchDB Single
• CouchDB Cluster

License

The software is provided under AGPL-3.0. Contributions to this project are accepted under the same license.

[dianabarsan]

For the record, this is the error that we expect when trying to upgrade from a version that does not use CouchDb 3.5 (any cht < 4.21):

2025-10-09 13:08:52 �[32mINFO�[39m: Saving ddocs for medic-users-meta 
2025-10-09 13:08:52 �[31mERROR�[39m: Error thrown while installing: Error: Error while saving docs: saving _design/:staged:users-meta failed with invalid_design_doc
    at Object.module.exports.saveDocs (/api/src/db.js:164:11)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async Object.saveStagedDdocs (/api/src/services/setup/utils.js:258:5)
    at async Object.stage (/api/src/services/setup/upgrade-steps.js:92:3)
    at async safeInstall (/api/src/services/setup/upgrade.js:40:5) {
  [stack]: 'Error: Error while saving docs: saving _design/:staged:users-meta failed with invalid_design_doc\n' +
    '    at Object.module.exports.saveDocs (/api/src/db.js:164:11)\n' +
    '    at processTicksAndRejections (node:internal/process/task_queues:96:5)\n' +
    '    at async Object.saveStagedDdocs (/api/src/services/setup/utils.js:258:5)\n' +
    '    at async Object.stage (/api/src/services/setup/upgrade-steps.js:92:3)\n' +
    '    at async safeInstall (/api/src/services/setup/upgrade.js:40:5)',
  [message]: 'Error while saving docs: saving _design/:staged:users-meta failed with invalid_design_doc'
} 

This error would occur immediately after hitting the upgrade/stage button, while API tries to start indexing the new version's views.

[sugat009]

@dianabarsan what is the workaround for this?

[dianabarsan]

That deployments update to v 4.21 before the version with this fix.

[github-actions]

This PR is now marked "stale" after 30 days without activity. It will be closed automatically in 10 days unless you add a comment, push new changes or remove the "stale" label.