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/app/plugins/cli.py

@@ -0,0 +1,58 @@
+"""Plugin management CLI (SPEC §11.1).
+
+    python -m app.plugins.cli list
+    python -m app.plugins.cli install <name>
+    python -m app.plugins.cli uninstall <name> [--drop-data]
+
+Builtin (core) plugins refuse uninstall.
+"""
+
+from __future__ import annotations
+
+import argparse
+
+from app.plugins import loader, migrate
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = argparse.ArgumentParser(
+        prog="python -m app.plugins.cli", description="Manage webmail plugins"
+    )
+    sub = parser.add_subparsers(dest="cmd", required=True)
+    sub.add_parser("list", help="list discovered plugins")
+    p_install = sub.add_parser("install", help="apply a plugin's migrations")
+    p_install.add_argument("name")
+    p_uninstall = sub.add_parser("uninstall", help="remove a plugin (refuses builtin)")
+    p_uninstall.add_argument("name")
+    p_uninstall.add_argument(
+        "--drop-data", action="store_true", help="also drop the plugin's tables"
+    )
+    args = parser.parse_args(argv)
+
+    if args.cmd == "list":
+        for plugin in loader.get_plugins():
+            kind = "builtin" if plugin.builtin else "removable"
+            migr = "migrations" if plugin.migrations else "no-migrations"
+            print(f"{plugin.name}\t{plugin.version}\t{kind}\t{migr}")
+        return 0
+
+    if args.cmd == "install":
+        migrate.install(args.name)
+        print(f"installed {args.name}")
+        return 0
+
+    if args.cmd == "uninstall":
+        try:
+            migrate.uninstall(args.name, drop_data=args.drop_data)
+        except loader.PluginRemovalError as exc:
+            print(f"error: {exc}")
+            return 1
+        suffix = " (data dropped)" if args.drop_data else " (data kept)"
+        print(f"uninstalled {args.name}{suffix}")
+        return 0
+
+    return 1
+
+
+if __name__ == "__main__":  # pragma: no cover
+    raise SystemExit(main())