Add installer/script delivery metadata to the core software model

AppVersion gains sha256 and silentargs so the endpoint update_app push can pin exact installer bytes and carry per-version silent switches; Application gains installersha256 for the app-level install source. New ShopDB-hosted script library (Script model plus scripts API) backs run_script delivery, with the body fetched by digest on push rather than pre-staged or sent over the command wire. Two idempotent migrations with real downgrades. Script added to the shopdb.api contract surface for plugin use.

tests/test_core/test_appversion_delivery.py

@@ -0,0 +1,42 @@
+"""AppVersion installer-delivery metadata: sha256 + silentargs.
+
+These two per-version fields feed the endpoint installer push: sha256 pins the
+exact bytes the agent fetches, and silentargs carries the version's unattended-
+install switches. The API must accept and echo both, and the model must
+serialize them.
+"""
+
+
+def _create_app(client, auth_headers, appname='DeliveryApp'):
+    resp = client.post('/api/applications',
+                       json={'appname': appname, 'isinstallable': True},
+                       headers=auth_headers)
+    return resp.get_json()['data']['appid']
+
+
+def test_create_version_accepts_and_echoes_delivery_metadata(client, db, auth_headers):
+    """POST versions with sha256 + silentargs; the response carries both back."""
+    appid = _create_app(client, auth_headers)
+    digest = 'a' * 64
+    resp = client.post(f'/api/applications/{appid}/versions',
+                       json={'version': '1.2.3',
+                             'sha256': digest,
+                             'silentargs': '/S /v/qn'},
+                       headers=auth_headers)
+    assert resp.status_code == 201
+    data = resp.get_json()['data']
+    assert data['sha256'] == digest
+    assert data['silentargs'] == '/S /v/qn'
+
+
+def test_version_delivery_metadata_defaults_to_null(client, db, auth_headers):
+    """A version created without delivery metadata serializes both as null,
+    so a version that predates the push feature reads cleanly."""
+    appid = _create_app(client, auth_headers, appname='NoMetaApp')
+    resp = client.post(f'/api/applications/{appid}/versions',
+                       json={'version': '0.9.0'},
+                       headers=auth_headers)
+    assert resp.status_code == 201
+    data = resp.get_json()['data']
+    assert data['sha256'] is None
+    assert data['silentargs'] is None

tests/test_core/test_public_read_surface.py

@@ -83,6 +83,15 @@ PUBLIC_ENDPOINTS = {
     # requesting user. Same reasoning as endpoints.report_command_result in
     # tests/test_core/test_authz.py.
     'endpoints.claim_next_command',
+
+    # The endpoint agent downloads an installer package for an update_app
+    # command. Authenticated inside the handler by the endpoints collector API
+    # key - the same shape as claim_next_command - because a bay has no user
+    # session. Queueing the update_app command is the actual authority and stays
+    # gated on endpoints.deploy, audited with the requesting user.
+    'endpoints.download_app_package',
+    'endpoints.download_app_package_by_app',
+    'endpoints.download_script_body',
 }
 
 # Reads that need a LOGIN but no named permission, because the handler decides