feat(server): the authorization pattern, with "Your devices"

Serverpod has no row-level security, so every endpoint enforces access itself, by three rules established here once: the person comes from the session, never from the client, and every query filters by them; someone else's row answers exactly like a missing one (NotFoundException, shared in lib/src/common); endpoints for people with an identity declare requiredScopes: {identified} instead of checking it themselves.

DevicesEndpoint is the first such endpoint: it lists your sessions and signs one of them out, for a lost phone. It uses the existing session table, so no migration. Serverpod's own helpers are unguarded (revokeSession deletes by id alone; listSessions without authUserId returns everyone's sessions), so the endpoint puts the owner check into the same query and then notifies the revoked device as revokeSession does. Each query carries its SQL as a comment.

The identified scope lives in lib/src/auth/scopes.dart. grantIdentified gives it to a person and to their existing session rows, because sessions keep the copy of the scopes they were started with; step 9 uses it.

Tests assert the refusals first: anonymous people and callers who aren't signed in are refused; the list shows only your own devices; signing out someone else's device fails exactly like an unknown id and leaves it alone; grantIdentified reaches existing sessions. The shared fixtures live in test/integration/support. AGENTS.md names the endpoint as the reference and warns about the unguarded helpers.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

AGENTS.md

@@ -95,6 +95,9 @@ A spaced-repetition learning app: studysets of flashcards, reviewed on an FSRS s
 - **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.
 - **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**: content tables carry `audience`, `keyId` (null = not yet encrypted), `payload` (`ByteData`) and `nonce`. Content fields live inside `payload`, so the server can't sort or search by them.
 - **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.