Editions (Date-Anchored Defaults)

Source of truth: docs/prd/editions.md. This skill is the contributor-facing decision tree for "does my change need edition handling", not a restatement of the architecture — read docs/prd/editions.md for the four-layer model, pkg/edition/journal.go's Entry schema, and the guardrail tests before touching anything. This skill exists because the deciding question ("does this default change supersede prior behavior?") is easy to answer wrong by only checking the literal rule ("new keys are never journal-gated") without checking what the rule is for.

The decision tree

Ask these in order. Stop at the first "yes."

1. Does this change a previously-shipped key's literal default value? (e.g. flipping settings.terminal.pager's struct default from "true" to "false".)