diff --git a/server/CLAUDE.md b/server/CLAUDE.md
index f7198bd82..305c7adeb 100644
--- a/server/CLAUDE.md
+++ b/server/CLAUDE.md
@@ -46,7 +46,7 @@ Nest owns everything. Every domain is a DI module under `src/nest/<domain>/` (`c
 - **Thin controller → injectable provider.** Never resurrect a plain function-module service; don't grow god services — split a domain into several modules when it outgrows one class (trips and auth already are).
 - **Inject, don't reach for module globals.** No imports of the global `db` proxy from `nest/` layers at all any more — the last production importer converted onto a repository, and the export now survives only so ~190 test files' `vi.mock('…/db/database', …)` factories keep typechecking; no new code depending on the `ws` singleton or event-sink globals. There is no `DatabaseService` to inject either — take the repository(ies) you need plus `UnitOfWork` for transactions. Modules must be importable without side effects.
 - **Transactions are not optional.** Multi-statement writes go in `await this.uow.transactional(async () => …)` (`UnitOfWork` from `nest/database`, provided by the global `OrmModule`); never hand-roll `BEGIN`/`COMMIT` and never call `db.transaction()` (the Phase 1 async sweep removes it). Every DB-touching method is `async`; `@typescript-eslint/no-floating-promises` and `no-misused-promises` are errors, so an unawaited call or a `Promise` in a condition fails lint. Bind values with `?`; identifiers only via a literal allow-list.
-- **Migrations are append-only.** A migration is identified by its class name in `mikro_orm_migrations`, and files sort by the timestamp in that name — never rename or delete one that has shipped, and never edit its body; add a new one. No env interpolation in SQL. (The old positional `schema_version` array and the hand-kept `db/migrations.ts` test builder are both gone; the numbered migrations are the only schema history, for tests too.)
+- **Migrations are append-only.** A migration is identified by its class name in `mikro_orm_migrations`, and files sort by the timestamp in that name — never rename or delete one that has shipped, and never edit its body; add a new one. No env interpolation in SQL. (The old positional `schema_version` array and the hand-kept `db/migrations.ts` test builder are both gone; the numbered migrations are the only schema history, for tests too.) A new foreign key comes with an index that leads with its column(s), or deleting the parent scans the child table; `tests/unit/db/foreign-key-indexes.test.ts` fails on one without.
 - **Every write endpoint validates** through the Zod pipe with a schema from `@trek/shared` — no `Record<string, unknown>` + ad-hoc checks. Also verify every referenced id exists and belongs to the same trip.
 - **Every outbound `fetch`** gets a timeout, a response-size cap and boundary validation — no `as`-casting provider responses, no silent `catch → null`. User-influenced URLs go through the SSRF guard. Never fall back to another user's API key.
 - **Fail closed.** Unrecognized flag values mean OFF; sandbox/permission opt-outs refuse in production; never pick a less-safe path based on the *absence* of a file. GET handlers must not write.
diff --git a/server/tests/unit/db/foreign-key-indexes.test.ts b/server/tests/unit/db/foreign-key-indexes.test.ts
new file mode 100644
index 000000000..1aff9e4ef
--- /dev/null
+++ b/server/tests/unit/db/foreign-key-indexes.test.ts
@@ -0,0 +1,139 @@
+import type Database from 'better-sqlite3';
+import { afterAll, describe, expect, it } from 'vitest';
+import { createSnapshotTestDb } from '../../helpers/db-mock';
+
+/**
+ * Migration20200101042200 added 86 indexes by hand so that deleting a trip or a
+ * user stops scanning every child table while it holds the one connection. A
+ * hand-written list is a one-off, though: the next table with a trip_id or a
+ * user_id foreign key would bring the full scans back without a signal, and
+ * gen:entities regenerates entities without an @Index just as happily.
+ *
+ * This runs against the database the migrations build (the same snapshot every
+ * test opens) and requires that the columns of every foreign key lead some
+ * index or the primary key, in order, so SQLite can find the child rows of a
+ * parent by seeking instead of scanning. A foreign key that deliberately goes
+ * without one is listed in UNINDEXED_ALLOWED with the reason.
+ */
+
+/** `table.column` (comma-joined for a composite key) that may stay unindexed, each with its reason. */
+const UNINDEXED_ALLOWED: Record<string, string> = {};
+
+interface ForeignKeyRow {
+  id: number;
+  seq: number;
+  table: string;
+  from: string;
+}
+
+interface IndexListRow {
+  name: string;
+}
+
+interface IndexInfoRow {
+  seqno: number;
+  name: string | null;
+}
+
+interface TableInfoRow {
+  name: string;
+  pk: number;
+}
+
+const testDb = createSnapshotTestDb();
+
+afterAll(() => {
+  testDb.close();
+});
+
+function tables(db: Database.Database): string[] {
+  const rows = db.prepare(`SELECT name FROM sqlite_master WHERE type = 'table' AND name NOT LIKE 'sqlite_%'`).all() as {
+    name: string;
+  }[];
+  return rows.map((r) => r.name).sort();
+}
+
+/** Each foreign key of a table as its ordered child columns. */
+function foreignKeys(db: Database.Database, table: string): string[][] {
+  const rows = db.prepare(`PRAGMA foreign_key_list("${table}")`).all() as ForeignKeyRow[];
+  const byId = new Map<number, ForeignKeyRow[]>();
+  for (const row of rows) byId.set(row.id, [...(byId.get(row.id) ?? []), row]);
+  return [...byId.values()].map((group) => group.sort((a, b) => a.seq - b.seq).map((r) => r.from));
+}
+
+/** Every index of a table, and its primary key, as ordered column lists. */
+function indexedPrefixes(db: Database.Database, table: string): string[][] {
+  const lists: string[][] = [];
+  for (const { name } of db.prepare(`PRAGMA index_list("${table}")`).all() as IndexListRow[]) {
+    const cols = (db.prepare(`PRAGMA index_info("${name}")`).all() as IndexInfoRow[])
+      .sort((a, b) => a.seqno - b.seqno)
+      // An expression column has no name and ends the usable prefix.
+      .map((c) => c.name);
+    const usable: string[] = [];
+    for (const c of cols) {
+      if (c === null) break;
+      usable.push(c);
+    }
+    lists.push(usable);
+  }
+  const pk = (db.prepare(`PRAGMA table_info("${table}")`).all() as TableInfoRow[])
+    .filter((c) => c.pk > 0)
+    .sort((a, b) => a.pk - b.pk)
+    .map((c) => c.name);
+  if (pk.length) lists.push(pk);
+  return lists;
+}
+
+/** True when the foreign key's columns, in any order, are the leading columns of one index. */
+function isLedByIndex(fk: string[], indexes: string[][]): boolean {
+  const want = [...fk].sort().join(',');
+  return indexes.some((cols) => cols.length >= fk.length && [...cols.slice(0, fk.length)].sort().join(',') === want);
+}
+
+function unindexed(db: Database.Database): string[] {
+  const missing: string[] = [];
+  for (const table of tables(db)) {
+    const indexes = indexedPrefixes(db, table);
+    for (const fk of foreignKeys(db, table)) {
+      if (!isLedByIndex(fk, indexes)) missing.push(`${table}.${fk.join(',')}`);
+    }
+  }
+  return missing;
+}
+
+describe('foreign key indexes', () => {
+  it('FKIDX-001: every foreign key in the migrated schema leads an index or the primary key', () => {
+    const missing = unindexed(testDb).filter((key) => !(key in UNINDEXED_ALLOWED));
+    expect(missing, 'add a CREATE INDEX for each in a new migration, and an @Index on the entity').toEqual([]);
+  });
+
+  it('FKIDX-002: UNINDEXED_ALLOWED holds only keys that exist and are still unindexed', () => {
+    const now = new Set(unindexed(testDb));
+    expect(Object.keys(UNINDEXED_ALLOWED).filter((key) => !now.has(key))).toEqual([]);
+  });
+
+  it('FKIDX-003: the check fails on an unindexed foreign key and passes once it is indexed', () => {
+    const Sqlite = testDb.constructor as unknown as new (path: string) => Database.Database;
+    const db = new Sqlite(':memory:');
+    try {
+      db.exec(`
+        CREATE TABLE parent (id INTEGER PRIMARY KEY, a INTEGER, b INTEGER, UNIQUE (a, b));
+        CREATE TABLE child (id INTEGER PRIMARY KEY, parent_id INTEGER REFERENCES parent(id), note TEXT);
+        CREATE TABLE pair (x INTEGER, y INTEGER, z INTEGER, FOREIGN KEY (x, y) REFERENCES parent(a, b));
+        CREATE TABLE owned (parent_id INTEGER REFERENCES parent(id), slot INTEGER, PRIMARY KEY (parent_id, slot));
+      `);
+      // owned is covered by its primary key; child and pair are not.
+      expect(unindexed(db)).toEqual(['child.parent_id', 'pair.x,y']);
+
+      // An index that holds the column second does not help a lookup by it.
+      db.exec('CREATE INDEX idx_child_note_parent ON child(note, parent_id)');
+      expect(unindexed(db)).toContain('child.parent_id');
+
+      db.exec('CREATE INDEX idx_child_parent ON child(parent_id)');
+      db.exec('CREATE INDEX idx_pair_yx ON pair(y, x, z)');
+      expect(unindexed(db)).toEqual([]);
+    } finally {
+      db.close();
+    }
+  });
+});