This project is a Flutter app (frontend) backed by a Serverpod server (backend). Always build the app's backend with Serverpod.
Build for multiple users, use Serverpod's built-in authentication, which is already set up in `lib/server.dart`.
The user starts the server and Flutter app with `serverpod start`. There is no need to check if the server is running: make the changes and call the `serverpod` MCP tools as needed. If the server is not running, an informative error message will be received from the MCP server. Then STOP and ask the user to start it. NEVER start the server yourself. The Flutter app is started along with it, or can be launched from the MCP tool `spawn_flutter_app`.
While running, `serverpod start` watches for file changes to run incremental code generation and hot reload both the server and the Flutter app.
Calling `serverpod generate` directly is not needed, but might be useful to troubleshoot when an incremental generation fails.
ALWAYS use the MCP server instead of the command line. Use the MCP server to:
-`create_migration` and `apply_migrations` for database (after you change data models).
-`create_repair_migration` if the database has drifted out of sync with the migrations.
-`tail_server_logs` to read logs from the server.
-`tail_flutter_logs` to read the raw stdout/stderr of the Flutter app.
-`hot_reload` / `hot_restart` to reload or restart the server and the Flutter app. ALWAYS call `hot_restart` after doing changes in the Flutter app that may not work with normal hot reload (which is automatically applied).
-`spawn_flutter_app` to start a Flutter app declared under `serverpod: flutter_apps:` in the server `pubspec.yaml`.
-`get_flutter_app_dtd` (Dart tooling daemon) for connecting to the app through the `dart` MCP.
NEVER edit generated code. The server's `lib/src/generated/` directory and the whole `halkyon_learn_client` package are rewritten by the code generator. Change the `.spy.yaml` models, the endpoints, or `lib/server.dart` instead.
Migrations are a narrow exception: the `migration.sql` of a generated migration MAY be edited by hand when the generated SQL would lose data — to add a data transformation, or to reach a destructive change through non-destructive steps. Never touch the other files in the migration directory, and keep the schema the SQL ends up with identical to `definition.sql` — new databases are created from that file and never run `migration.sql`.
The `serverpod` MCP tools come from `.mcp.json`: `serverpod mcp-server`, a bridge to the running `serverpod start`. They load when a session starts; if they are missing, the server wasn't running or the session predates `.mcp.json`. Like all agent configuration, `.mcp.json` is git-ignored; in a fresh clone, create it with a server `serverpod` running `serverpod` with the arguments `--no-analytics mcp-server --server-dir halkyon_learn_server`.
**Pass `--no-analytics` to every `serverpod` call** (before the command: `serverpod --no-analytics generate`). Otherwise the CLI reports the commands run and the Serverpod features the project uses to PostHog; there is no setting or environment variable to switch that off. The VS Code task and `.mcp.json` pass it already.
Only when the server cannot be started at all, fall back to the CLI in the server package:
-`serverpod generate` to regenerate the client and the generated server code.
-`serverpod create-migration` after changing a model with a `table` (add `--force` for destructive changes). It only writes the migration; `serverpod start` applies pending migrations when it boots the server.
Tests need no Docker. `config/test.yaml` sets `database.dataPath`, so Serverpod starts and manages the test database (an embedded PostgreSQL) itself. Just run `dart test` in the server package.
Tooling traps: rules of `leancode_lint`'s analyzer plugin are ignored with its prefix (`// ignore: leancode_lint/missing_equatable_props`); `dart fix --apply` moves `flutter_driver` into the app's `dependencies` (as `any`) on every run, so restore it as a dev dependency (`sdk: flutter`) afterwards; never `dart format` generated code, only the hand-written paths, as `tool/check.sh` does; and never rebase or check out other commits while `serverpod start` runs: its watcher regenerates code for each intermediate state, leaves stale generated files behind and hot-reloads them. Stop it first, or work in a separate worktree.
-`tool/check.sh` (CLI): format check, `dart analyze --fatal-infos`, server and app tests. The pre-push hook runs the same script, so a push only goes through when it passes.
- Do `serverpod` MCP `hot_restart` if required (hot reload is done automatically). Will also hot restart Flutter app
- Check `serverpod` MCP `tail_server_logs` and `tail_flutter_logs` for any issues.
If the user asks you to test the app:
1. Use `get_flutter_app_dtd` (`serverpod` MCP) to get the Flutter app's DTD
2. Pass the DTD to `connect_dart_tooling_daemon` (`dart` MCP) to connect to the app
3. Use `flutter_driver` (`dart` MCP) to navigate through the app
The app is launched from `halkyon_learn_flutter/lib/driver.dart`, which starts the Flutter driver extension with text entry emulation turned off so the app stays usable by hand. To let the driver type, set `enableTextEntryEmulation: true` there and `hot_restart` the app.
A spaced-repetition learning app: studysets of flashcards, reviewed on an FSRS schedule. Content is rich text (`appflowy_editor` documents) everywhere. Targets: Linux, Windows, macOS, Android, iOS. There is no web build.
- **Packages**: `halkyon_learn_server` (endpoints, models, migrations), `halkyon_learn_client` (generated, never edited), `halkyon_learn_flutter` (the app, ID `app.halkyon.learn`).
- **Instances**: anyone may run one. The app takes the server URL from `--dart-define=SERVER_URL=…`, so never hard-code a host.
- **Working notes**: if `NEXT.md` exists in the repository root, read it first. It holds the current step, the plan and the reasoning behind each decision. It is local and never committed.
- **The agent implements; the developer decides.** Put every decision to the developer before building (design choices, alternatives, framework defaults kept or changed). The first time a new pattern appears (e.g. the first repository/gateway pair, the first synced model, the first endpoint with its denial tests), walk through it in detail with the developer; afterwards, implement exceedingly similar cases directly and point out only deviations.
- **Tests come first** and state the specification. Every access rule gets a test that asserts **denial**, not only permission.
- **Explain every migration's SQL.**
- **Before keeping a framework default, name the alternatives** and recommend one, especially where a choice becomes expensive once users or data exist.
- Every decision carries its reason (in `NEXT.md` or an ADR under `docs/adr/`).
- **Commits** are GPG-signed and carry a DCO `Signed-off-by` trailer (`git commit -s`; a local `prepare-commit-msg` hook adds it automatically).
- **Pushes** pass `tool/check.sh` first, through a local `pre-push` hook (in a fresh clone: `ln -s ../../tool/check.sh .git/hooks/pre-push`). CI runs it again, and a green `main` deploys itself (see *CI and deploys*), so an unsigned commit on `main` blocks every deploy after it.
- **Lints**: LeanCode's strict set (`leancode_lint`), configured once in the root `analysis_options.yaml`, which also enables its analyzer plugin. Plugins can only be enabled at the root of a pub workspace and only reach packages whose options include that file, so the server and the app include it; the generated client doesn't. Every `// ignore:` gets a comment saying why (`document_ignores`). The server switches off the four rules for Dart v3.13's constructor syntax (`use_primary_constructors`, `use_declaring_parameters`, `empty_container_bodies`, `unnecessary_type_name_in_constructor`): Serverpod's code generator (checked with v4.0.3) can't parse that syntax in endpoint files yet.
- **Feature-first.** App: `lib/src/core/` holds infrastructure shared by features, `lib/src/feature/<name>/` everything a user would name, and `lib/src/app/` puts the features together (the person's app and its router, the only code that knows them all). Server: `lib/src/<feature>/` holds that feature's `.spy.yaml` models and endpoints. Code moves into `core/` only once a second feature needs it. Why: a feature is added, changed or removed in one place.
- **Four layers per app feature**, dependencies pointing strictly downward: `widget/` (UI; reads bloc state, sends events) → `bloc/` (UI state; orchestrates repositories) → `data/` (repositories and gateways) → `model/` (immutable domain types; pure Dart, no Flutter, no I/O). A widget never calls a gateway; a model never imports a bloc.
- **Generated protocol classes are not domain models.** They carry the envelope (`payload` as bytes); `model/` holds the decoded content. Mapping between them happens in `data/`.
- **Import `halkyon_learn_client` with a prefix (`as protocol`) or a `show` list.** The generator emits a `<Model>Repository` for every table, and its names clash with the app's own repositories.
- **Gateway / repository.** A gateway is a thin boundary to *one* backend (e.g. the Serverpod client's endpoints) behind an `abstract interface class`. A repository is what features use: it composes gateways and holds the logic. Blocs depend on repositories, never on gateways or the raw client. Why: gateways are the seams tests fake, and adding the offline layer later becomes a new local gateway, not a rewrite of every feature.
- **Manual dependency injection.** One `Dependencies` object (`lib/src/core/dependencies/`) is the composition root, built at startup (`Dependencies.create()`) and exposed through the `DependenciesScope` InheritedWidget. It hands features repositories only. No service locator, no DI framework, no globals (the scaffold's global `client` moved into it). Why: every dependency is a typed, greppable field, and nothing is resolved by magic.
- **One graph per context.** The dependency graph belongs to one instance and one signed-in person; when either changes, a `KeyedSubtree` disposes the whole subtree and rebuilds it. Why: nothing from one person's session (blocs, streams, caches) can leak into another's.
- **App-wide vs. per person.** `Dependencies` holds what outlives a person (the client, auth). Everything of the signed-in person (their local database, its sync, their repositories) is `PersonDependencies`, opened by `PersonScope` inside `SessionGate`'s keyed subtree (`Dependencies.openPerson`) and disposed with it; widgets reach it through `PersonScope.of(context)`.
- **Every person has an app of their own** (`PersonApp`, `lib/src/app/`), which `SessionGate` builds inside the keyed subtree: a `MaterialApp.router` with its own `GoRouter`, and `PersonScope` around the router's navigator (`MaterialApp.builder`). So every screen and dialog is inside the person's scope and reads their repositories from `PersonScope.of(context)` wherever it is built, and a change of person disposes the router with every screen on it and starts again at home. Until someone is signed in, `SessionGate` shows a plain `MaterialApp`: the spinner, or the failure with a way to try again.
- **Platform plugins sit behind small interfaces in `Dependencies`**, with fakes in tests: picking files (`FilePicker`, `file_selector`), playing sounds (`SoundPlayer`, `audioplayers`), reading Anki packages on another isolate (`AnkiPackageReader`; a widget test's fake clock can't wait for one).
- **State: `flutter_bloc`, uniformly.** Blocs fold repository streams into immutable states with value equality, are provided as close to their consumer as possible, and log through one global `BlocObserver`. Why: the data layer is stream-shaped, event → state machines test without widgets, and one pattern everywhere is itself the point.
- **Value equality comes from `equatable`**, mixed in (`with Equatable`), for models and states alike; `leancode_lint`'s `missing_equatable_props` catches a field left out of `props`.
- **Rich text is `RichContent`** (`lib/src/core/content/`): the editor's document JSON plus a `formatVersion`, pure Dart, so models and the server can use it. `lib/src/core/editor/` converts it to and from the editor's `Document` and holds the one editing widget (`RichContentEditor`) and the one read-only renderer (`RichContentView`).
- **Time comes from `clock.now()`** (`package:clock`), never `DateTime.now()`, in server and app. Why: scheduling, streaks and expiry are deterministic under test (`withClock`, `fakeAsync`), and because Serverpod itself reads `clock.now()` (e.g. session expiry), `withClock` controls its behaviour too.
- **UTC for storing and sending, local time for display and day boundaries.** Serverpod sends `DateTime` as UTC and stores it in `timestamp without time zone` columns. Compare and compute in UTC; call `.toLocal()` only to display. "Due today", streaks and daily goals use the learner's **local** calendar day, computed on the client; the server never needs day boundaries.
- **Build configuration comes from `--dart-define`.** The client holds no secrets, ever.
- **Material comes from `package:material_ui`** (Cupertino from `package:cupertino_ui`), never from `package:flutter/material.dart`, which Flutter deprecates from its November 2026 release on. Packages still on the SDK's copy get the app's theme and localizations through `MaterialUiCompatibilityBridge` in `MaterialApp.builder`; remove it once they have moved.
- **Navigation is `go_router`**: the routes in `lib/src/app/app_router.dart`, their paths in `core/router/route_paths.dart`. Four tabs (Home, Library, Explore, Profile) are the branches of a `StatefulShellRoute`, each keeping its own stack of screens alive while another tab shows (`tabsContainer`, go_router's indexed stack plus `TabVisibility`, which a screen depends on to stop something once its tab is hidden); `AppShell` shows them as a navigation rail from 600 dp on and as a navigation bar below, and choosing the open tab again returns to its first screen. A tab's own screens are routes nested in its branch, reached with `context.go` (a studyset's screen in the library), and a studyset's topic opens on top of it with `context.push` (the same route, keyed by id, so several can stack); the breadcrumb's steps go up with `context.go`, so back then leads further up. What needs the whole window (studying, a card, settings) is a top-level route over the tabs, reached with `context.push`. Explore stays empty until something is shared.
- **Routes carry ids, never objects.** A screen finds its item in the repository's live list with `FoundById` (`core/widget/`): a spinner until the list arrives, then the item, or a screen saying it no longer exists (deleted on another device, or an old link). A screen that deletes its item closes, and keeps showing the item while it goes. Why: every location can be built from its path alone, and no screen goes on showing something that has gone.
- **The look is one theme** (`core/theme/`): `appTheme(brightness)` with hand-written light and dark colour schemes around the brand's cobalt and copper; `Theme.of(context).extras` (`ThemeExtras`) for the colours Material has no role for (states, the four FSRS ratings, a starred star); `PaletteColor` for the 20 colours a person can give content. `theme_test.dart` holds text to WCAG AA contrast (4.5:1) on each palette colour and on the dark theme's primary colour and surface. Layouts follow Material 3's window-size classes (`context.windowSize`, `core/layout/`), and running text stays within `readableContentMaxWidth`. Icons are Lucide (`lucide_icons_flutter`), except a starred star, which needs the fill Lucide lacks; the Material icons left in older screens go when those are restyled. Shared widgets are in `core/widget/` (`SectionCard`, `AppLoadingIndicator`, `confirmDestructiveAction`, `FoundById`, `TitleWithKicker`, `ContentCountsLine`, `showUndoSnackBar`, `ScrollHidingFab`, `PaletteColorPicker`, and the sheets below).
- **Forms and pickers open as sheets**: `showAdaptiveSheet` with a `SheetScaffold` (title and close button on top, the body scrolling, the action pinned below) shows a bottom sheet below expanded windows and a dialog from there on. A sheet that asks before discarding changes (a `PopScope`) passes `swipeable: false`: a bottom sheet swiped away closes without asking its `PopScope` (Flutter issue 152120, open with v3.47). A sheet offering an Undo passes `hasSnackBars: true`, so its snack bars show on it rather than behind its barrier. A picker that changes something outside it reports every change as it happens (`onChanged`) rather than as its result, since a sheet swiped away has none.
- **Text comes from `AppLocalizations`** (Flutter's gen-l10n, `lib/l10n/app_en.arb`; English only for now): no string a person reads is written into a widget, except in older screens until they are restyled. The generated `lib/l10n/app_localizations*.dart` are committed and never edited, analysed or formatted by hand. `flutter pub get` writes them anew, so CI fails when they don't match the `.arb` file.
- **By layer**: models with plain unit tests; repositories against fake gateways; blocs by asserting the emitted state sequence; widgets pumped in isolation, presentation widgets fed with ready-made data.
- **Server endpoints are tested for real** against the embedded Postgres (`withServerpod`, `dart test` in the server package), including the denial tests.
- **Test dependencies come from a test factory**, `testDependencies(...)` in `test/support/test_dependencies.dart`, filling in fakes by default (a factory in `lib/` couldn't reach the fakes in `test/`), so a new dependency changes one place. Don't make dependencies nullable to spare tests: that moves null checks into production code.
- Shared fakes live in `test/support/`; fakes pre-stub their streams so an incidental subscription doesn't fail the test.
- **Editor in widget tests**: host `AppFlowyEditor` in a scrollable body with a fixed-height slot (an over-constrained `Expanded` hangs the test), and `pump(const Duration(seconds: 1))` after editor changes to flush its timers. Test the document ↔ JSON round-trip as plain unit tests.
- **No `Stream.first` on a repository's stream in code that widget tests run**: `first` waits for the subscription's cancel future, which for a broadcast stream is a completed future of the root zone, so under the widget test's fake clock it never completes. Read once with the repository's `all()` instead. For the same reason a repository never keeps a completed future to chain later work on (a `Future.value()` made in `setUp` runs what waits for it in the real zone): a queue of writes starts empty and empties again when idle (`SerialQueue`, `core/async/`), and a cache keeps values, not futures (`GeoMapRepository`). Assets are read for real, which the fake clock doesn't advance: a widget test showing a map gets the maps read beforehand (`loadedMaps(tester)` into `testDependencies(maps: ...)`).
- **Server tests of what writes synced rows** run on the sync engine's database, as the server does (the generated test tools build the pod without it): pass the interceptor to `withServerpod`, call `initializeOfflineSync` in `setUp`, and write as a person through `transactionForUser`. Its writes take transactions of their own, so these tests turn rollback off and delete what they made (`test/integration/asset/asset_test.dart`).
- **Sync tests run against a running server** (ADR 0001, rule 9: the client's and the server's sync engines can't share one process): `halkyon_learn_flutter/test/sync/`, tagged `requires-server`, skipped by `tool/check.sh`; run them with `flutter test -t requires-server` while `serverpod start` runs. Every device is a client with in-memory session storage and its own local database, with the app's real gateway and repository on top; tests sync explicitly. What only the operator could see (a blanked payload, a row that must not exist) is checked with SQL against the development database, through the embedded PostgreSQL's Unix socket where there is one. An honest device only syncs the spaces the server announces, so a forged write never leaves it; the server's own check against modified clients (`_assertCanMergeInboundSpace` in the sync engine) has no test yet. They live in the app package because the server's Docker build resolves the server's dependencies without the client package. They must not initialize a Flutter test binding (no `testWidgets`), which would replace real HTTP with a mock.
- **Widget tests of screens start the whole app**: `pumpApp(tester, testDependencies(...), location: …)` (`test/support/pump_app.dart`) pumps `SessionGate` with the real `PersonApp`, opened at the screen's path, and settles once `PersonScope` has opened the person's data. From there a test moves as a person would: `openTab` (the tab's label alone may also be a screen's title), taps, `pageBack`. Data goes into the fake gateways before pumping; they work in memory (`FakeStudysetGateway`, with `failReads` for the error path), and a repository of the test's own on the same fake gateway writes what the app then reads. `pumpAndSettle` never ends while a spinner shows (`AppLoadingIndicator` animates without end): pump frames instead where one is expected. A widget pumped on its own that reads `AppLocalizations` needs `AppLocalizations.localizationsDelegates` in its `MaterialApp`.
- **CI** (`.forgejo/workflows/ci.yaml`) runs `tool/check.sh` on every push, on the Forgejo runner on sahaquiel (`deploy/runner/`). Jobs run directly on the host as the unprivileged user `runner`, never in containers: Docker access would be root on the production server. The runner's systemd unit keeps jobs away from production (no `/home`, no Docker socket, Docker's container networks unreachable, memory and CPU capped); keep it that way when changing it. `runner` has user ID 61000 and must never share one with a container's processes (PostgreSQL and the server run as 999, not remapped): the same user ID can read their environment and files. The job's first step (*Sandbox*) fails if any of this leaks. Flutter is pinned in the workflow (`FLUTTER_VERSION`): move it together with the local one. The server tests there get throwaway passwords from the environment (`SERVERPOD_…`, new for every job), since `passwords.yaml` is never committed; without them they exit with code 1 and no message (Serverpod's own template does the same). CI also runs `serverpod generate` and fails if the committed generated code differs from its output. CI runs on pushes only: a pull request from a fork would run its code on the production server.
- **A green `main` deploys learn.halkyon.eu** through `deploy/redeploy.sh`, the only command the runner's key may run as `deploy` (pinned in `authorized_keys`, from sahaquiel itself only). It deploys the commit CI checked while it is still the tip, as a fast-forward, only if every new commit is signed by a key in `deploy/allowed-signers` (the deployed copy decides), after dumping the database (the last 3 dumps stay in `~deploy/backups`: the way back from a deploy, not backups), applies the migrations in a run of their own before switching (`--role=maintenance --apply-migrations`: a failing migration stops the deploy while the old server keeps serving, so migrations must keep the old server working until the switch), and fails unless the new server answers. A failed deploy leaves the checkout at the deployed commit; run the workflow again to retry. By hand: `ssh sahaquiel-deploy halkyon-learn/deploy/redeploy.sh <commit>`. Never `docker compose down -v` there.
- **Authentication**: server-side sessions (`ServerSideSessionsConfigFromPasswords`), not JWT, for immediate revocation. Scopes are copied onto the session row, so changing a person's scopes means updating their session rows too.
- **Identity**: `AuthUser` is the person; identity providers (anonymous, GitHub) attach to it. Content references `AuthUser`, never a provider account.
- **GitHub keeps only the numeric GitHub ID**: our own slim login (`lib/src/auth/github.dart`) on Serverpod's GitHub helpers; Serverpod's stock GitHub login endpoint, which stores name, email and avatar, is never exposed. GitHub sign-in is on only where the passwords hold `githubClientId` and `githubClientSecret` (in production `GITHUB_CLIENT_ID`/`GITHUB_CLIENT_SECRET` in `deploy/.env`); the app asks `instance.info()`.
- **Linking keeps the person** (`GitHubUpgradeEndpoint`, `requireLogin`): the GitHub ID joins the signed-in anonymous person, who becomes identified and loses the anonymous identity, in one transaction. **Signing in** (`GitHubSignInEndpoint`) only reaches people who have a GitHub account already, and only without a session: Serverpod refuses to issue another person's session inside a signed-in call. Refusals are `GitHubSignInRefusedException` with a reason.
- **Switching devices' person** (the app's `switchToGitHub`): swap the session directly, never through "signed out" (which would start another anonymous account), then end the anonymous session left behind.
- **On Linux and Windows the browser half is the app's own** (`LoopbackWebAuth`, `feature/auth/data/`): the system browser and a loopback address (RFC 8252), put in place of flutter_web_auth_2's own implementation (checked with v5.1.0) before each sign-in. The package's front ends every pending sign-in when the app is resumed, and on the desktop the window regaining focus resumes it, so its loopback server closed before GitHub answered. Ours waits for GitHub, the profile's Cancel (shown only there), choosing another tab, a change of person, or 5 minutes; the regression test drives the package's front through a focus change. Remove it once the package stops ending sign-ins on focus there. Serverpod (v4.0.3) reports every cancelled browser round trip as an unknown error, so the gateway knows a cancel only by having asked for it; a cancel on GitHub's own page, or leaving the browser on Android, still shows "Couldn't sign in with GitHub."
- **Authorization lives in endpoint code**; Serverpod has no row-level security. Load content filtered by the session's `authUserId`, never by an owner ID the client sends. A row another person owns must be indistinguishable from a missing one. Features involving other people require the `identified` scope, declared via `requiredScopes`, never checked ad hoc.
- **The reference is `DevicesEndpoint`** (`halkyon_learn_server/lib/src/auth/`) with its tests: the owner check sits in the same query (`WHERE "id" = $1 AND "authUserId" = $2`), zero rows means `NotFoundException` (shared, `lib/src/common/`), and every rule has a test that asserts the refusal. Each query carries its SQL as a comment.
- **Serverpod's own helpers aren't guarded**: `ServerSideSessions.revokeSession` deletes by id alone, and `listSessions` without `authUserId` returns everyone's sessions. Never pass them anything a client sent.
- **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. Since blanking can't be undone, an Undo comes before it: `StudysetDeletions`, opened with the person's data, keeps every studyset deletion that can still be undone; lists leave out what it reports as pending, and once the time to undo is over it deletes the whole subtree, what is inside first, each studyset's cards blanked before it. Widgets delete and undo through it directly (`deleteStudysetWithUndo`), not through a bloc: deleting a studyset from its own screen closes that screen and its bloc, and the deletion and its Undo must outlive them. It closes first with the person's data and drops what still waits. Tags differ, being values (a tag is its name, ADR 0004 rule 2): one is blanked and deleted at once, and its Undo makes a tag of that name and colour anew, on the same cards. 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, 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.
- **Reviews are an append-only log** (`ReviewLog`: card, rating, `reviewedAt` in UTC, `durationMs`). A card's schedule is never stored: `scheduleOf` (`feature/study/model/card_schedule.dart`) replays its reviews in time order with FSRS-6 (`fsrs`, pinned exactly), and only the final due date is fuzzed, from the card's id and review count, so every device computes the same. Studying a studyset covers everything inside it but archived studysets (`studiedIn`), and the study queue (`study_queue.dart`) takes each studyset's cards as a group: due cards of all of them earliest first, then each studyset's new cards in tree order, 20 per studyset and local day. The library's and the topics' counts and badges add up the same way. Deleting a card deletes its reviews.
- **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.
- **Tree, tags, modes, settings and files** (ADR 0004): a studyset's `parent` and sibling `position` form the tree, and studysets in a cycle or without their parent show at the top level (`topLevel`); its `archivedAt`, `starredAt` and `updatedAt` are columns, and every change of a studyset writes `updatedAt` with it (the library lists starred studysets first, then the most recently changed); a card's tags are `card_tag` rows, one per assignment, never updated, and a duplicate counts once; `review_log.mode` is `review`, `reverse` (its own schedule) or `cram` (never moves a schedule), and a schedule replays the reviews of one mode; `person_settings` is meant as one row per person, and extra rows fold into the one with the smallest id; an `asset` row stands for a file in private cloud storage, found by its hash. **Never derive a row's id from a person or anything else guessable**: ids are unique across the whole table, so someone could claim it first in their own space and break the owner's sync.
- **Files** (ADR 0004, rule 5): `AssetEndpoint` (`requireLogin`) takes uploads into the caller's own space by SHA-256 (`startUpload` gives Serverpod's upload description, or null when the file is there already and claims it anew; `finishUpload` keeps it only if its content has that hash) and serves an asset row's file to its space's owner and members only, `NotFoundException` otherwise, also for a deleted row (the sync engine hides tombstones). Files live in the private database storage at `spaces/<space>/<sha256>`, at most 20 MB each, and within limits (`file_limits.dart`, from the environment: an anonymous person 100 MB, an identified one 500 MB or what a `file_allowance` row grants them, the instance 15 GB), checked when an upload starts (unfinished uploads count, or they could fill the disk unnoticed) and again when it finishes (only what is kept counts), refused with `FileLimitExceededException`; `deletePerson` deletes the person's files and allowance, and `FilePruningFutureCall` deletes daily those no live row refers to (or never finished), 7 days after they were last claimed. In the app, `AssetRepository` (`core/asset/`) keeps files by hash in the person's folder (`files/`, uploads waiting marked in `files/uploads/`), uploads after each sync that went through, and downloads on demand, checking the hash; every hash is checked to be one before it becomes part of a path. Content names a file by the URL `asset:<asset row id>` (`assetUrl`, `RichContent.assetIds`): images are the editor's `image` block, sounds an `audio` block (`core/editor/file_blocks.dart`), and any other URL is never fetched. `StoredFileImage` loads through the repository like Flutter's `NetworkImage`, keyed by the person's repository too, so no image crosses people.
- **Imported cards** say where they came from in their first revision's payload (`origin`, card schema 3, e.g. `anki`); the dashboard doesn't count them as written. The Anki import (`feature/anki/`) reads `.apkg`/`.colpkg` packages of every format on an isolate of its own (`AnkiPackageReader`), zstd through our fork of `pure_zstd` (Anki's frames don't record their size), and its fixtures come from Anki itself (`tool/anki/make_fixtures.py`).
- **Every client migration keeps a device's rows** (`test/core/sync/device_migration_test.dart` replays each on a database with a row in every synced table of ours; SQLite rebuilds tables to add foreign keys, which Serverpod's runner does with foreign keys off). A new synced table needs a row in that test, which fails until it has one.
- **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.
- **Serverpod's version moves together with `serverpod_offline_sync`**, which pins Serverpod exactly: the root `pubspec.yaml` overrides the four core packages to the project's version. Upgrade Serverpod only together with those overrides and the CLI version CI generates code with (`SERVERPOD_VERSION` in `.forgejo/workflows/ci.yaml`), after reading the sync package's changelog.
- **The source-code link**: both licences require offering the source of what an instance runs to the people who use it. `instance.info().sourceCodeUrl` names it (the operator's `SOURCE_URL`, else this project's repository) and the app's About dialog shows it next to the licences and every package's notice. Keep it working when changing the dialog or the endpoint.
- **Deleting a person** goes through `deletePerson` (`lib/src/auth/account.dart`), in one transaction and in ADR 0001 rule 6's order: their sessions end first (a device with a valid session would re-upload everything), then their space goes with all its content through the foreign keys, then the person with their identities. `AccountEndpoint.delete` deletes the caller; the app also calls it when an anonymous account is given up (signed out of, or switched away from to GitHub), since nobody could ever sign into it again.
- **Pruning**: `PruningFutureCall` deletes anonymous people unused for 90 days, daily, scheduled when the server starts. Scheduling a future call always adds an entry, so the server cancels the previous one by its identifier first.
- **One person's data per device**: `PersonFolders` wipes every other person's folder when a person's data opens: their sessions ended on this device. Opening waits for the previous person's database to close.
- **Session logs are not persisted** (`persistentEnabled: false` in every run mode) for privacy. Don't re-enable them.
- **Secrets** live in `halkyon_learn_server/config/passwords.yaml` (git-ignored). Never change `serverSideSessionKeyHashPepper`: it would sign everyone out, and anonymous accounts can't sign back in.
- **Linux builds need** `libwebkit2gtk-4.1-dev`, `libsecret-1-dev`, and for sounds (`audioplayers`) `libgstreamer1.0-dev` and `libgstreamer-plugins-base1.0-dev`. If a Linux build tries to install to `/usr/local`, the CMake cache is stale: delete `build/linux`.
