Browser support in Webpacker depends on both Babel and UglifyJS; mismatched settings can break legacy browsers like IE11 even when JavaScript is transpiled.

Haml 6 renders most custom attributes verbatim, so falsy values no longer remove them. Boolean attributes keep special handling, and Haml::BOOLEAN_ATTRIBUTES can extend that list.

Rails forms can assign tag associations in several ways, from array columns to join models; nested attributes keep tag changes in one transaction.

Redis cache connections in Rails can be tuned with custom timeouts, reconnect behavior, and error handling to avoid slow cache operations and missed connection failures.

ActiveRecord base errors do not render in Simple Form by default; they need explicit handling to display form-wide validation messages.

Prioritizing refactoring and upgrade work is harder in larger projects; a maintained technical-debt summary helps compare effort, customer value, and developer value.

Abused sign-up and password-reset emails can turn applications into spam relays when user input is reflected in messages. CAPTCHAs, rate limits, and avoiding arbitrary text reduce the risk.

Native smooth scrolling has no built-in completion signal; scrollTo() and scrollIntoView({ behavior: 'smooth' }) do not return promises, so a scroll idle timeout can wait for the animation to finish.

Rails can map selected exceptions to non-500 responses and suppress error monitoring noise, such as returning 404 for missing records or denied access.

Custom RSpec matcher for checking allowed association values, useful when validating assignable_values on model associations.

Duration#ago and Duration#from_now return ActiveSupport::TimeWithZone, which can introduce unexpected timezone behavior when an app assumes local or timezone-unaware dates.

Strict loading in index actions catches N+1 queries when views touch unpreloaded associations, causing test failures instead of hidden database hits.

Rails response tests can parse bodies by MIME type with parsed_body, replacing manual JSON.parse(response.body) in many cases and enabling cleaner assertions.

Prevent race conditions when multiple Ruby processes read or write the same file by using flock for exclusive locking, optionally via a companion .lock file.

@extend reuses Sass selectors, but multi-file bundling can duplicate imported styles and break the expected selector merging.

Template and eval coverage in Ruby can be tracked with SimpleCov from Ruby 3.2 onward, including Haml and ERB templates.

Rails migrations can change column types without dropping data by using custom SQL casting, but rollback may fail when values cannot be converted.

Create tiny test videos with ffmpeg by lowering resolution, framerate, and bitrate to keep files small while preserving duration.

Capistrano deployments can fail with ssh-ed25519 keys because net-ssh needs ed25519 and bcrypt_pbkdf; stale host fingerprints in ~/.ssh/known_hosts can also block access.

Personal issue workflow checklist for moving features from start to review, with branch, commit, merge request, testing, and staging handoff steps.

Boolean fields in Rails are safer with database defaults and NOT NULL constraints; application-level fallbacks are brittle, especially for tri-state values and instance-dependent defaults.

Gem installations waste time generating local docs that are rarely used; disabling documentation by default speeds up manual installs with gem and ~/.gemrc.

External images in emails can fail in some clients; inline attachments with Rails and attachments.inline keep images visible, but turn messages into multipart emails and use content IDs.

Rails 7 app data can be stored as encrypted attributes with deterministic lookup support, but search, grouping, and bulk updates become limited.