Use JSON-format structured logging in production

[mwtrew]

Status

• Related to https://github.com/RaspberryPiFoundation/digital-editor-issues/issues/1455

What's changed?

• Adds the Semantic Logging gem and uses it to make log messages more useful. See a comparison here.
  • This includes controller and action names by default.
• In the production environment only, logs are structured in JSON-format to make filtering easier in BetterStack.
  • Example: filtering down to GET requests on the FeaturesController.
  • The change in application.rb looks like it also enables JSON logging in non-prod environments, however this only applies to the log files written to disk, not the logging output in standard out.
• Disables Flipper logging, which was at DEBUG level with no clear way of changing the level.

Steps to perform after deploying to production

None.

[github-actions]

Test coverage

91.72% line coverage reported by SimpleCov.
Run: https://github.com/RaspberryPiFoundation/editor-api/actions/runs/27693546397

[Copilot]

Pull request overview

This PR introduces rails_semantic_logger to improve Rails log signal (e.g., controller/action payloads) and configures JSON structured logging for production output (intended for BetterStack/Heroku).

Changes:

• Add rails_semantic_logger (and semantic_logger) dependencies.
• Configure production logging to emit JSON to STDOUT when RAILS_LOG_TO_STDOUT is set, and set an application identifier.
• Adjust Flipper logging configuration (explicitly disabled).

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Gemfile.lock	Adds rails_semantic_logger and semantic_logger dependencies.
Gemfile	Adds rails_semantic_logger to the app dependencies.
config/initializers/flipper.rb	Explicitly disables Flipper check logging (comment needs to match behavior).
config/environments/production.rb	Configures JSON logging to STDOUT on Heroku via Semantic Logger settings.
config/application.rb	Sets Semantic Logger app name and (currently) globally sets JSON format.

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[abcampo-iry]

Looks reasonable to me