parentOf() re-inferred the IMAP hierarchy separator from each folder's name,
relying on an unenforced invariant (displayName == fullName.substringAfterLast(
separator)) established three layers from where ImapClient reads the
authoritative JavaMail folder.separator and then discards it.
Carry that separator through FetchedFolder -> FolderEntity -> Folder and split a
folder's parent on it. Fall back to the old name inference only for legacy rows
whose delimiter is null, until the next folder refresh (delete-then-insert)
backfills the real value.
Adds a nullable folders.hierarchyDelimiter column via a Room v14 -> v15 migration
with the exported v15 schema, and registers MIGRATION_14_15 in DatabaseModule so
existing v14 installs actually upgrade (provideDatabase configures no destructive
fallback, so an unregistered migration would crash every upgrading user).
Tests: JVM unit tests for parentOf() (persisted vs. null delimiter, incl. the
case where inference cannot locate the parent) and the FetchedFolder->entity
round-trip; an instrumented v14->v15 migration test plus the chain-replay
assertion.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
JMR-devandClaude Fable 5
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