implement session deletion on data layer

data/session_repo.js

@@ -65,6 +65,8 @@ export default class SessionRepo {
   static async #handleChange() {
     if (!(this instanceof Session))
       throw new TypeError("session to put in must be an actual Session");
+    if (!(SessionRepo.#marker in this))
+      return;
     SessionRepo.put(this, this[SessionRepo.#marker]);
   }
 
@@ -173,6 +175,29 @@ export default class SessionRepo {
       (session) => SessionRepo.#setupChangeHandling(session, transaction.db));
   }
 
+  /** Delete a specific session.
+   *
+   * This also tears down the auto updating if the passed session is an
+   * instance of `Session`.
+   *
+   * @param {number | Session} session The session or session ID to delete.
+   * @param {Transactable=} transaction A transaction to use.
+   */
+  static async delete(session, transaction) {
+    transaction = toTransaction(transaction, [WbDb.OS_SESSIONS], "readwrite");
+    let sessions = transaction.objectStore(WbDb.OS_SESSIONS);
+
+    if (session instanceof Session) {
+      session.removeEventListener(Session.EVENT_CHANGE, SessionRepo.#handleChange);
+      delete this[SessionRepo.#marker];
+      session = session.id;
+    }
+    if (typeof session !== "number")
+      throw new TypeError("session to delete must be session or session ID");
+
+    return requestToPromise(sessions.delete(session));
+  }
+
   /** Load all sessions, parse them, then reinsert them.
    *
    * Does not set the intermediate objects up for change handling.

data/session_repo.test.js

@@ -207,6 +207,21 @@ export default function() {
       assert.strictEqual(sessions[1].id, second.id, "second is older");
     });
 
+    QUnit.test("delete session", async function(assert) {
+      inst = WbDb.get(true);
+      await waitForOpen(inst);
+
+      let session = new Session();
+      await SessionRepo.put(session, inst);
+      let stored = await SessionRepo.get(session.id, inst);
+      assert.notStrictEqual(stored, undefined, "session stored");
+      assert.strictEqual(stored.id, session.id, "IDs match");
+
+      await SessionRepo.delete(session.id, inst);
+      stored = await SessionRepo.get(session.id, inst);
+      assert.strictEqual(stored, undefined, "no longer stored");
+    });
+
     QUnit.test("reinserting all sessions", async function(assert) {
       // old structurized session (see v1 tests of session model)
       const old = {