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docs: ADR 0003, card revisions with a list of parents, merged per side

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Records step 10's decisions with their reasons and the alternatives weighed: a list of parents instead of ADR 0001's single parentRevisionId (a revision with two parents resolves a conflict), a three-way merge per side against the newest common ancestor (no silent merge inside a side), and an explicit fractional position for the order. ADR 0001 gets an "Amended by" line, and AGENTS.md points to the new ADR.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>
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Tizian 「ティツィアーン」 2026-09-30 15:08:27 +02:00
commit ec246e552d
Signed by: raisondetredev
GPG key ID: 07F6FCF405488B64
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AGENTS.md
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@ -117,7 +117,7 @@ A spaced-repetition learning app: studysets of flashcards, reviewed on an FSRS s
- **Granting a scope** goes through a function like `grantIdentified`, which updates the person *and* their session rows.
- **Content envelope**: synced content tables carry `keyId` and `nonce` (nullable; `null` = plaintext, the only value, ADR 0002 rule 6) and `payload` (`ByteData`): UTF-8 JSON with a `schemaVersion`, encoded and decoded by one codec per feature (e.g. `studyset_payload.dart`) on top of `core/content/payload.dart`, which also holds the blanked `redactedPayload`. Content fields live inside `payload`: a new field raises the schema version instead of migrating a synced table, which would lock older app versions out of syncing (ADR 0002, rule 3). A payload in a newer schema is skipped with a log, never shown half-read.
- **Synced data** (`database: sync`, `serverpod_offline_sync`, ADR 0001): every person has their own local SQLite database (`<app support>/people/<authUserId>/sync.sqlite`). Its gateway writes through the `OfflineSyncDatabaseSession`, **names the columns of every update**, and calls `SyncService.requestSync()` after every write; the repository re-reads after its own writes and when a sync merged changes (`remoteChanges`). `SyncService` syncs on triggers (at start, 2 s after the last write, on resume, every 5 min), one sync at a time. **Deleting blanks the payload first** (ADR 0002, rule 2): the engine keeps deleted rows until the space is deleted. Order by the UUID v7 id (ADR 0001, rule 7). Access to synced rows is the engine's: a person syncs their personal space and the spaces granted to them; the endpoint rules above guard everything that isn't synced.
- **Content people edit is append-only revisions** (ADR 0001, rule 2; the reference is `CardRevision`): a revision is never updated except to blank it, and `parents` lists the revisions it replaces. A save's parents are all current heads, which is also how a conflict is resolved. `mergeRevisions` (`feature/card/model/card_merge.dart`) merges several heads per side against their newest common ancestor; a side changed differently is a conflict the person settles, never merged silently. Deleting blanks every revision, then deletes.
- **Content people edit is append-only revisions** (ADR 0001 rule 2, ADR 0003; the reference is `CardRevision`): a revision is never updated except to blank it, and `parents` lists the revisions it replaces. A save's parents are all current heads, which is also how a conflict is resolved. `mergeRevisions` (`feature/card/model/card_merge.dart`) merges several heads per side against their newest common ancestor; a side changed differently is a conflict the person settles, never merged silently. Deleting blanks every revision, then deletes.
- **Order is a fractional index** (`fractional_indexing_dart`, rocicorp's algorithm) in its own column, last writer wins. Two devices appending at once can pick the same key, so ties sort by id.
- **Every synced table indexes `spaceId`** (`indexes: <table>_space_idx: fields: spaceId`, e.g. `studyset.spy.yaml`): deleting a space cascades into every synced table, and Postgres doesn't index foreign keys by itself, so account deletion and pruning would otherwise read whole tables.
- **The client's local migration** (in `halkyon_learn_client/lib/migrations/`, written by the same `create-migration`) creates the device's SQLite schema from the whole definition, so it also contains the server's own tables. Only the synced tables and the bookkeeping ever hold data on a device.