M3 plugin platform: SDK + loader, RLS-isolated tables, migrations, jobs

Backend foundation for the plugin platform (SPEC §11), Phases 1-3.

Phase 1 — SDK + loader:
- app/plugins/types.py: frozen Plugin/UiManifest/Slot/Page/JobSpec contract.
- app/plugins/sdk.py: sdk(name) facade — the only app.* import allowed for plugins
  (scoped session, plugin.{name}.* publish, blob, outbox, settings, SSRF http_get, KV, enqueue).
- app/plugins/loader.py: entry-point discovery (webmail.plugins), hook forwarding
  (API + worker), router mounting at /api/plugins/{name}, ui-manifest aggregation.
- plugin_kv core table (migration 0013) + GET /api/plugins/ui-manifest.

Phase 2 — non-removable core plugins + DB-enforced privacy:
- builtin flag (calendar/contacts will be builtin=True; uninstall refuses them).
- RLS per-user isolation on plg_* tables: least-privilege webmail_plugin role
  (migration 0014), plugin_session(user_id) sets LOCAL ROLE + app.current_user_id,
  rls.enable_rls() (ENABLE+FORCE RLS + USING/WITH CHECK policy). Mail untouched.
- Per-plugin Alembic runner (shared env, dedicated version table) + install/uninstall
  --drop-data CLI; skeleton fixture proves install -> run -> uninstall --drop-data
  leaves zero residue (§12 M3 acceptance).

Phase 3 — plugin jobs (§11.2):
- JobSpec registered as arq function plg.{plugin}.{func} + cron (5-field parser);
  singleton=True guarded by a per-(plugin,user) Redis lock; wired onto the shared
  interactive worker.

Gates: ruff, mypy --strict (94 files + tests), full suite 326 passed. RLS isolation,
migration round-trip, and singleton lock covered by tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Rcj3TpydMTzTSmU7kunzf8

backend/tests/plugins/test_migrate.py

@@ -0,0 +1,89 @@
+"""Per-plugin migration runner + install/uninstall lifecycle (SPEC §11.1, §12 M3).
+
+The runner drives Alembic synchronously (env.py calls asyncio.run), so it's
+invoked via ``asyncio.to_thread`` from these async tests to avoid a nested loop.
+"""
+
+from __future__ import annotations
+
+import asyncio
+from pathlib import Path
+
+import pytest
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import get_settings
+from app.plugins import loader, migrate
+from app.plugins.sdk import Plugin
+
+_VERSIONS = str(Path(__file__).parent.parent / "fixtures" / "plugin_demo" / "versions")
+
+
+async def _scalar(sql: str, **params: str) -> object:
+    engine = create_async_engine(get_settings().database_url, poolclass=NullPool)
+    try:
+        async with engine.connect() as conn:
+            return (await conn.execute(text(sql), params)).scalar()
+    finally:
+        await engine.dispose()
+
+
+async def _regclass(name: str) -> object:
+    return await _scalar("SELECT to_regclass(:n)", n=name)
+
+
+async def _cleanup() -> None:
+    engine = create_async_engine(get_settings().database_url, poolclass=NullPool)
+    try:
+        async with engine.begin() as conn:
+            await conn.execute(text("DROP TABLE IF EXISTS plg_demo_note"))
+            await conn.execute(text("DROP TABLE IF EXISTS alembic_version_plg_demo"))
+    finally:
+        await engine.dispose()
+
+
+async def test_install_run_uninstall_dropdata_roundtrip() -> None:
+    loader.set_plugins_for_test([Plugin(name="demo", version="1.0", migrations=_VERSIONS)])
+    try:
+        await asyncio.to_thread(migrate.install, "demo")
+
+        # Table exists, RLS is enabled on it, and the per-plugin version table is present.
+        assert await _regclass("plg_demo_note") == "plg_demo_note"
+        assert await _scalar(
+            "SELECT relrowsecurity FROM pg_class WHERE relname = 'plg_demo_note'"
+        ) is True
+        assert await _regclass("alembic_version_plg_demo") == "alembic_version_plg_demo"
+
+        # --drop-data removes the table AND the version table: zero residue.
+        await asyncio.to_thread(migrate.uninstall, "demo", drop_data=True)
+        assert await _regclass("plg_demo_note") is None
+        assert await _regclass("alembic_version_plg_demo") is None
+    finally:
+        await _cleanup()
+
+
+async def test_uninstall_without_drop_data_keeps_the_table() -> None:
+    loader.set_plugins_for_test([Plugin(name="demo", version="1.0", migrations=_VERSIONS)])
+    try:
+        await asyncio.to_thread(migrate.install, "demo")
+        await asyncio.to_thread(migrate.uninstall, "demo", drop_data=False)
+        assert await _regclass("plg_demo_note") == "plg_demo_note"  # data preserved
+    finally:
+        await asyncio.to_thread(migrate.uninstall, "demo", drop_data=True)
+        await _cleanup()
+
+
+async def test_uninstall_refuses_builtin_plugin() -> None:
+    loader.set_plugins_for_test(
+        [Plugin(name="calendar", version="1", builtin=True, migrations=_VERSIONS)]
+    )
+    with pytest.raises(loader.PluginRemovalError, match="builtin"):
+        await asyncio.to_thread(migrate.uninstall, "calendar", drop_data=True)
+
+
+async def test_install_unknown_plugin_errors() -> None:
+    loader.set_plugins_for_test([])
+    with pytest.raises(migrate.PluginMigrationError, match="unknown"):
+        await asyncio.to_thread(migrate.install, "nope")