Invoice totals can miss cents when rounding is done too late or with floats; rounded item totals and BigDecimal keep net, VAT and gross consistent.

Finding the opposite of an ActiveRecord scope is tricky with NULL values and older Rails versions; invert_where, subqueries, or Arel can negate conditions safely.

MySQL snapshot reads in REPEATABLE READ can hide concurrent changes, so counts and updates drift unless locking starts before the first query.

Different ways to build HTML-safe markup in Rails helpers affect readability, buffering, and XSS safety. concat, safe_join, capture, and html_safe each behave differently.

Random values in factories make tests flaky and hide failures; fixed defaults and sequences keep test data predictable.

Shared test setup makes example files harder to read and change; self-contained examples keep tests clearer and easier to extend.

Complex Ruby regular expressions become easier to read with %r alternative delimiters and the /x flag for whitespace and comments.

MySQL text fields use four storage sizes with byte limits, and limit maps to the smallest fitting type. Choosing the wrong size can waste space or truncate data.

Regular expressions in JavaScript use RegExp objects or regex literals, and global matches keep state between test() calls.

Elasticsearch licensing changes force a move to OpenSearch, with parallel clusters and reindexing to preserve search service continuity.

HTML video autoplay can fail on page load or without user interaction, and there is no native failure event. Checking paused after media loads reveals whether playback started.

Rails performance debugging often hides slow SQL, view rendering, and N+1 queries; rack-mini-profiler helps surface bottlenecks during development.

SAML logout can be initiated by the service provider or identity provider, with browser redirects or backchannel POSTs; devise_saml_authenticatable needs specific Rails and Keycloak logout handling.

Rails 7.1 changes production logging to standard out, which can break file-based logs in opscomplete setups unless the previous logger configuration is restored.

rem breakpoints in @media queries can ignore a set root font size and shift at the browser default instead, causing unexpected responsive behavior.

Git submodules in GitLab CI can fail with permission errors when cloning private repositories into other projects. Access restrictions on CI token usage must be loosened or allowlisted.

Async functions can be made cancelable with AbortSignal and AbortController; rejecting with AbortError matches browser APIs and improves compatibility.

Cucumber::MultilineArgument::DataTable#diff! caches state, so repeated checks inside patiently do keep failing; expected_table.dup.diff! avoids the stale comparison.

Local Keycloak can emulate a SAML identity provider for development, letting SSO flows and attribute mapping be tested without waiting on an external IDP.

HTTPS requests to hosts with an expired certificate can stay safe by accepting only one known certificate instead of disabling verification entirely.

Cron jobs can miss their scheduled run because of network or hardware failures, so recurring work should resume safely after delays by tracking the last successful execution.

html and body default to content height, so absolutely positioned footer elements may miss the viewport bottom; min-height: 100% or 100vh keeps pages full height.

Ruby percent notation creates symbols, arrays, regexes and shell output with compact literals and interpolation support.