Legacy Area to Place backfill

This guide covers Dawarich 1.20.0.

DataMigrations::BackfillAreasIntoPlacesJob runs on data_migrations and calls Places::AreasBackfill. Lazy resolution through Places::LegacyAreaAdapter uses the same migration for an existing unmapped Area.

Legacy Area names can exceed Place's 255-character limit. The backfill copies only the first 255 characters into a created or promoted Place, without adding an ellipsis. Ruby character slicing preserves valid multibyte strings. Names of 255 characters or fewer are copied unchanged. If the first 255 characters are all whitespace, leading whitespace is removed before taking the prefix so the Place name remains nonblank. The original Area row keeps its full name; no schema migration or public API validation change is needed.

Matching still compares the full normalized Area name (trimmed and lowercased) and requires a Place within 50 metres. It does not compare truncated prefixes: different long names sharing their first 255 characters get separate Places. A Place already mapped from a long Area is excluded when that original normalized identity differs from the incoming Area, including when the incoming name equals the truncated prefix. This protects either migration order. A full normalized match may promote an existing Place, subject to the existing ambiguity and note-date collision checks.

The stable LegacyAreaPlaceMapping makes a completed backfill restartable. Area notes move to the mapped Place with their contents intact. Area-only visits retain their IDs and gain the Place association; existing label, ownership and visit-conflict rules still apply. The legacy Area remains.

After upgrading to code containing this fix, a failed long-name backfill can be retried from Sidekiq's Retry or Dead set. If the job is no longer present, an operator can enqueue DataMigrations::BackfillAreasIntoPlacesJob.perform_later in the application's Rails console. Completed mappings are skipped; genuinely invalid Areas are still reported and cause a retry after other Areas migrate. Do not delete legacy Areas or mappings as a retry workaround.

Regression coverage: spec/regressions/area_backfill_truncates_long_names_spec.rb exercises 255/256/300 characters, multibyte names, shared prefixes, promotion, lazy resolution, preserved notes/visits and repeat runs. Existing service specs cover ambiguous matches, note-date conflicts and invalid-record reporting.

Related issue: #3930.