WarpEngine 0.5.0: a catalog that can say a title is not yours

A desktop client reading /api/software had no way to learn that a title costs
money. There was nothing in the response to say so, no way to sign in, and no
way to be told "you do not own this" — so a store with paid titles could only
hand the client a 403 at download time and let it guess why.

The fix belongs here rather than in the client. A client serves more than one
store, so anything it knows about a particular one has to arrive from that
store's own API; a rule compiled into the client is a rule that breaks every
other catalog it reads. Three seams, each following the storage adapter's
shape — documented contract, default that is byte for byte the old behaviour,
one config key to replace it:

- **access policy** — visible_software_scope / access_for / authorize_download.
  Every catalog entry now carries an `access` block (gated, entitled, price,
  purchaseUrl, webUrl) and both /api/download and /file/* ask before serving.
  The vocabulary is deliberately generic: a word from one host's domain would
  make every client that reads it specific to that host.
- **client sign-in** — the device authorization grant (RFC 8628), over the
  host's own user model. The approval page stays the host's, because approving
  needs a session and HTML. Tokens are ApplicationTokens with a `catalog`
  scope, so publishing and reading stay separable.
- **service descriptor** — GET /api/service says what this deployment is and
  whether it has a sign-in at all, which is how a client stops guessing.

With no policy and no subject class configured — every deployment today — the
API is unchanged: /api/auth/* answers 404, /api/service reports auth: null, and
the 187 pre-existing examples pass untouched.

A policy that raises is treated as a refusal, not permission. An artifact
served because the gatekeeper crashed is the one failure mode this must not
have, so a broken policy empties the catalog and denies the download.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

spec/dummy/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_08_06_000002) do
+ActiveRecord::Schema[8.1].define(version: 2026_08_19_000001) do
   create_table "application_tokens", id: { type: :bigint, unsigned: true }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.datetime "created_at", precision: 3
     t.datetime "deleted_at", precision: 3
@@ -29,6 +29,24 @@ ActiveRecord::Schema[8.1].define(version: 2026_08_06_000002) do
     t.index ["token_digest"], name: "idx_application_tokens_token_digest", unique: true
   end
 
+  create_table "device_grants", id: { type: :bigint, unsigned: true }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "application_token_id", unsigned: true
+    t.datetime "approved_at", precision: 3
+    t.string "client_name", limit: 128
+    t.datetime "created_at", precision: 3
+    t.datetime "denied_at", precision: 3
+    t.string "device_code", limit: 64, null: false
+    t.datetime "expires_at", precision: 3, null: false
+    t.string "issued_token", limit: 64
+    t.bigint "subject_id", unsigned: true
+    t.string "subject_type", limit: 128
+    t.datetime "updated_at", precision: 3
+    t.string "user_code", limit: 16, null: false
+    t.index ["device_code"], name: "idx_device_grants_device_code", unique: true
+    t.index ["expires_at"], name: "idx_device_grants_expires_at"
+    t.index ["user_code"], name: "idx_device_grants_user_code", unique: true
+  end
+
   create_table "downloads", id: { type: :bigint, unsigned: true }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.datetime "created_at", precision: 3
     t.datetime "deleted_at", precision: 3