diff --git a/backend/app/api/__init__.py b/backend/app/api/__init__.py
index ef003a1..30490ff 100644
--- a/backend/app/api/__init__.py
+++ b/backend/app/api/__init__.py
@@ -16,6 +16,7 @@ def register_routers(app: FastAPI) -> None:
     from app.api.compose import router as compose_router
     from app.api.mailboxes import router as mailboxes_router
     from app.api.messages import router as messages_router
+    from app.api.plugins import router as plugins_router
     from app.api.recipients import router as recipients_router
     from app.api.saved_searches import router as saved_searches_router
     from app.api.search import router as search_router
@@ -36,6 +37,13 @@ def register_routers(app: FastAPI) -> None:
         settings_router,
         mailboxes_router,
         saved_searches_router,
+        plugins_router,
     ):
         app.include_router(router, prefix="/api")
     app.include_router(ws_router, prefix="/api")
+
+    # Mount discovered plugin routers at /api/plugins/{name} (SPEC §11). Hooks are
+    # subscribed in the lifespan startup so they register once per process.
+    from app.plugins import loader
+
+    loader.mount_routers(app)
diff --git a/backend/app/api/plugins.py b/backend/app/api/plugins.py
new file mode 100644
index 0000000..1c57262
--- /dev/null
+++ b/backend/app/api/plugins.py
@@ -0,0 +1,23 @@
+"""Plugin platform HTTP surface (SPEC §11).
+
+Currently just the aggregated UI manifest the frontend loader fetches on boot.
+Individual plugin routers are mounted separately at ``/api/plugins/{name}`` by
+:func:`app.plugins.loader.mount_routers`.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from fastapi import APIRouter
+
+from app.identity.deps import CurrentUser
+from app.plugins import loader
+
+router = APIRouter(prefix="/plugins", tags=["plugins"])
+
+
+@router.get("/ui-manifest")
+async def ui_manifest(user: CurrentUser) -> dict[str, Any]:
+    """Slots, pages, and capabilities declared by all installed plugins (SPEC §11.3)."""
+    return loader.build_ui_manifest()
diff --git a/backend/app/main.py b/backend/app/main.py
index d998e9f..6ff12b9 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -18,6 +18,12 @@ async def lifespan(app: FastAPI) -> AsyncIterator[None]:
     """Warm shared resources on startup, dispose them on shutdown."""
     # Touch settings early so misconfiguration fails fast.
     get_settings()
+    # Subscribe plugin hooks so events published in the API process reach them
+    # (worker-published events are handled by the worker's own registration).
+    from app.events import get_event_bus
+    from app.plugins import loader
+
+    loader.register_hooks(get_event_bus())
     yield
     await close_redis()
     await dispose_engine()
diff --git a/backend/app/models.py b/backend/app/models.py
index 44c3517..68cd7f9 100644
--- a/backend/app/models.py
+++ b/backend/app/models.py
@@ -8,6 +8,7 @@ from __future__ import annotations
 
 import datetime as dt
 import uuid
+from typing import Any
 
 from sqlalchemy import (
     BigInteger,
@@ -288,6 +289,23 @@ class SavedSearch(Base):
     pinned: Mapped[bool] = mapped_column(nullable=False, server_default=text("true"))
 
 
+class PluginKv(Base):
+    """Namespaced key/value store for plugins (SPEC §11 ``plugin_kv``).
+
+    Core-owned infrastructure (not a ``plg_``-prefixed plugin table): every plugin
+    gets a slice keyed by (plugin, user_id, key). ``value`` is arbitrary JSON.
+    Invariant I-7 (user-data rows carry ``user_id``) holds here too."""
+
+    __tablename__ = "plugin_kv"
+
+    plugin: Mapped[str] = mapped_column(Text, primary_key=True)
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("users.id", ondelete="CASCADE"), primary_key=True
+    )
+    key: Mapped[str] = mapped_column(Text, primary_key=True)
+    value: Mapped[Any] = mapped_column(JSONB, nullable=False)
+
+
 class KnownRecipient(Base):
     __tablename__ = "known_recipients"
     __table_args__ = (
diff --git a/backend/app/plugins/__init__.py b/backend/app/plugins/__init__.py
new file mode 100644
index 0000000..8a8f9ae
--- /dev/null
+++ b/backend/app/plugins/__init__.py
@@ -0,0 +1,6 @@
+"""Plugin platform (SPEC §11).
+
+Public surface for plugin authors is :mod:`app.plugins.sdk`; the loader and
+core wiring live here but plugins must not import them directly (SPEC §11:
+"plugins may not import from ``app.*`` internals other than ``app.plugins.sdk``").
+"""
diff --git a/backend/app/plugins/alembic/env.py b/backend/app/plugins/alembic/env.py
new file mode 100644
index 0000000..f9d9ec4
--- /dev/null
+++ b/backend/app/plugins/alembic/env.py
@@ -0,0 +1,39 @@
+"""Shared Alembic environment for plugin migration branches (SPEC §11.1).
+
+Every plugin reuses this env; the runner (:mod:`app.plugins.migrate`) points
+``version_locations`` at the plugin's own revision directory and gives it a
+dedicated ``version_table`` (``alembic_version_plg_{name}``) so each plugin's
+migration history is independent of core and of every other plugin.
+"""
+
+from __future__ import annotations
+
+import asyncio
+
+from alembic import context
+from sqlalchemy.ext.asyncio import async_engine_from_config
+from sqlalchemy.pool import NullPool
+
+from app.config import get_settings
+
+config = context.config
+config.set_main_option("sqlalchemy.url", get_settings().database_url)
+_version_table = config.get_main_option("version_table") or "alembic_version"
+
+
+def _do_run_migrations(connection: object) -> None:
+    context.configure(connection=connection, version_table=_version_table)  # type: ignore[arg-type]
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+async def _run_online() -> None:
+    engine = async_engine_from_config(
+        config.get_section(config.config_ini_section, {}), prefix="sqlalchemy.", poolclass=NullPool
+    )
+    async with engine.connect() as connection:
+        await connection.run_sync(_do_run_migrations)
+    await engine.dispose()
+
+
+asyncio.run(_run_online())
diff --git a/backend/app/plugins/alembic/script.py.mako b/backend/app/plugins/alembic/script.py.mako
new file mode 100644
index 0000000..063ed2a
--- /dev/null
+++ b/backend/app/plugins/alembic/script.py.mako
@@ -0,0 +1,26 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+"""
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+revision: str = ${repr(up_revision)}
+down_revision: str | None = ${repr(down_revision)}
+branch_labels: str | Sequence[str] | None = ${repr(branch_labels)}
+depends_on: str | Sequence[str] | None = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}
diff --git a/backend/app/plugins/cli.py b/backend/app/plugins/cli.py
new file mode 100644
index 0000000..91d9958
--- /dev/null
+++ b/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())
diff --git a/backend/app/plugins/db.py b/backend/app/plugins/db.py
new file mode 100644
index 0000000..ece5ac9
--- /dev/null
+++ b/backend/app/plugins/db.py
@@ -0,0 +1,44 @@
+"""RLS-enforced database access for plugins (SPEC §11.1 + privacy hardening).
+
+``plugin_session(user_id)`` yields a normal SQLAlchemy session whose transaction
+has been dropped to the least-privilege :data:`~app.plugins.rls.PLUGIN_ROLE` and
+bound to the per-user RLS context. Both are set with transaction-local scope
+(``SET LOCAL`` / ``set_config(..., is_local=true)``), so they auto-revert on
+commit/rollback and cannot leak across pooled connections.
+
+Because the role is non-superuser / non-owner / NOBYPASSRLS, the row-level policy
+from :mod:`app.plugins.rls` is actually enforced: a plugin query that forgets to
+filter ``user_id`` still returns only the current user's rows, and it cannot write
+rows for anyone else (policy ``WITH CHECK``).
+"""
+
+from __future__ import annotations
+
+import uuid
+from collections.abc import AsyncIterator
+from contextlib import asynccontextmanager
+
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.db import get_sessionmaker
+from app.plugins.rls import PLUGIN_ROLE
+
+
+@asynccontextmanager
+async def plugin_session(user_id: uuid.UUID) -> AsyncIterator[AsyncSession]:
+    """A transactional session scoped to ``user_id`` under RLS (SPEC §11.1)."""
+    async with get_sessionmaker()() as session:
+        try:
+            # Bind the RLS user context first (while still the privileged role), then
+            # drop into the restricted role for the rest of the transaction.
+            await session.execute(
+                text("SELECT set_config('app.current_user_id', :uid, true)"),
+                {"uid": str(user_id)},
+            )
+            await session.execute(text(f"SET LOCAL ROLE {PLUGIN_ROLE}"))
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
diff --git a/backend/app/plugins/jobs.py b/backend/app/plugins/jobs.py
new file mode 100644
index 0000000..6d52874
--- /dev/null
+++ b/backend/app/plugins/jobs.py
@@ -0,0 +1,130 @@
+"""Plugin background jobs on the shared arq worker (SPEC §11.2).
+
+Each plugin ``JobSpec`` is registered as an arq function under a namespaced name
+``plg.{plugin}.{func}`` (enqueue on demand from hooks/routes via ``sdk.enqueue``),
+and, when it has a ``schedule``, also as an arq cron job. ``singleton=True`` wraps
+the job in a Redis NX lock keyed by (plugin, func, user) so at most one instance
+runs per user (or globally for scheduleds with no user). Jobs share the worker
+pool + retry semantics with core jobs and log under the ``plg`` logger.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+from arq import cron
+from arq.cron import CronJob
+from arq.worker import Function, func
+
+from app.plugins import loader
+from app.plugins.types import JobSpec, Plugin
+from app.redis_client import get_redis
+
+logger = logging.getLogger("plg")
+
+# Safety expiry on the singleton lock so a crashed job can't wedge a user forever.
+# A job that runs longer than this could overlap; acceptable for M3.
+_LOCK_TTL = 3600
+
+# Standard 5-field cron order and each field's inclusive value bounds.
+_FIELD_ORDER = ("minute", "hour", "day", "month", "weekday")
+_FIELD_BOUNDS = {
+    "minute": (0, 59),
+    "hour": (0, 23),
+    "day": (1, 31),
+    "month": (1, 12),
+    "weekday": (0, 6),
+}
+
+
+def job_name(plugin_name: str, spec: JobSpec) -> str:
+    """The arq function name a plugin job is registered under."""
+    return f"plg.{plugin_name}.{spec.func.__name__}"
+
+
+def _lock_key(plugin_name: str, func_name: str, user: object) -> str:
+    return f"plglock:{plugin_name}:{func_name}:{user}"
+
+
+def _make_runner(plugin: Plugin, spec: JobSpec) -> tuple[Any, str]:
+    """Wrap a job func with the singleton lock (when requested) + namespaced name."""
+    func_name = spec.func.__name__
+    name = job_name(plugin.name, spec)
+
+    async def runner(ctx: dict[str, Any], *args: Any, **kwargs: Any) -> Any:
+        if not spec.singleton:
+            return await spec.func(ctx, *args, **kwargs)
+        user = kwargs.get("user_id", "global")
+        key = _lock_key(plugin.name, func_name, user)
+        acquired = await get_redis().set(key, b"1", nx=True, ex=_LOCK_TTL)
+        if not acquired:
+            logger.info("%s skipped: singleton already running (user=%s)", name, user)
+            return None
+        try:
+            return await spec.func(ctx, *args, **kwargs)
+        finally:
+            await get_redis().delete(key)
+
+    return runner, name
+
+
+def plugin_arq_functions() -> list[Function]:
+    """Every plugin job as an arq function (enqueue-on-demand), namespaced."""
+    funcs: list[Function] = []
+    for plugin in loader.get_plugins():
+        for spec in plugin.jobs:
+            runner, name = _make_runner(plugin, spec)
+            funcs.append(func(runner, name=name))
+    return funcs
+
+
+def _parse_field(token: str, lo: int, hi: int) -> set[int] | None:
+    """Parse one cron field to a value set (``*`` -> None = every)."""
+    if token == "*":
+        return None
+    values: set[int] = set()
+    for part in token.split(","):
+        if part.startswith("*/"):
+            values.update(range(lo, hi + 1, int(part[2:])))
+        elif "-" in part:
+            start, end = part.split("-", 1)
+            values.update(range(int(start), int(end) + 1))
+        else:
+            values.add(int(part))
+    return values
+
+
+def parse_cron(expr: str) -> dict[str, set[int] | None]:
+    """Parse a standard 5-field cron string into arq ``cron`` field kwargs."""
+    parts = expr.split()
+    if len(parts) != 5:
+        raise ValueError(f"cron expression must have 5 fields (min hour dom mon dow): {expr!r}")
+    return {
+        name: _parse_field(token, *_FIELD_BOUNDS[name])
+        for name, token in zip(_FIELD_ORDER, parts, strict=True)
+    }
+
+
+def plugin_cron_jobs() -> list[CronJob]:
+    """Cron-scheduled plugin jobs as arq ``CronJob``s (run on the shared worker)."""
+    jobs: list[CronJob] = []
+    for plugin in loader.get_plugins():
+        for spec in plugin.jobs:
+            if spec.schedule is None:
+                continue
+            runner, name = _make_runner(plugin, spec)
+            f = parse_cron(spec.schedule)
+            jobs.append(
+                cron(
+                    runner,
+                    name=f"{name}.cron",
+                    second=0,
+                    minute=f["minute"],
+                    hour=f["hour"],
+                    day=f["day"],
+                    month=f["month"],
+                    weekday=f["weekday"],
+                )
+            )
+    return jobs
diff --git a/backend/app/plugins/kv.py b/backend/app/plugins/kv.py
new file mode 100644
index 0000000..fc8bc15
--- /dev/null
+++ b/backend/app/plugins/kv.py
@@ -0,0 +1,63 @@
+"""Namespaced key/value store handed to plugins (SPEC §11 ``plugin_kv``).
+
+A :class:`PluginKv` is bound to one (plugin, user_id) slice of the core
+``plugin_kv`` table; values are arbitrary JSON. This is the light-state store
+every plugin gets — heavy plugins use their own ``plg_``-prefixed tables (§11.1).
+"""
+
+from __future__ import annotations
+
+import uuid
+from typing import Any
+
+from sqlalchemy import delete, select
+from sqlalchemy.dialects.postgresql import insert as pg_insert
+
+from app.db import session_scope
+from app.models import PluginKv
+
+
+class PluginKvStore:
+    """CRUD over one plugin's per-user KV slice. Instantiate via ``sdk.kv(user_id)``."""
+
+    def __init__(self, plugin: str, user_id: uuid.UUID) -> None:
+        self._plugin = plugin
+        self._user_id = user_id
+
+    async def get(self, key: str, default: Any = None) -> Any:
+        async with session_scope() as session:
+            row = await session.get(PluginKv, (self._plugin, self._user_id, key))
+            return row.value if row is not None else default
+
+    async def set(self, key: str, value: Any) -> None:
+        """Upsert ``key`` -> ``value`` (JSON-serialisable)."""
+        stmt = (
+            pg_insert(PluginKv)
+            .values(plugin=self._plugin, user_id=self._user_id, key=key, value=value)
+            .on_conflict_do_update(
+                index_elements=[PluginKv.plugin, PluginKv.user_id, PluginKv.key],
+                set_={"value": value},
+            )
+        )
+        async with session_scope() as session:
+            await session.execute(stmt)
+
+    async def delete(self, key: str) -> None:
+        async with session_scope() as session:
+            await session.execute(
+                delete(PluginKv).where(
+                    PluginKv.plugin == self._plugin,
+                    PluginKv.user_id == self._user_id,
+                    PluginKv.key == key,
+                )
+            )
+
+    async def items(self) -> dict[str, Any]:
+        """Return every key/value in this plugin+user slice."""
+        async with session_scope() as session:
+            rows = await session.execute(
+                select(PluginKv.key, PluginKv.value).where(
+                    PluginKv.plugin == self._plugin, PluginKv.user_id == self._user_id
+                )
+            )
+            return dict(rows.all())  # type: ignore[arg-type]
diff --git a/backend/app/plugins/loader.py b/backend/app/plugins/loader.py
new file mode 100644
index 0000000..526c026
--- /dev/null
+++ b/backend/app/plugins/loader.py
@@ -0,0 +1,148 @@
+"""Plugin discovery + core wiring (SPEC §11).
+
+Discovers plugins via the ``webmail.plugins`` entry-point group, then:
+- mounts each plugin router at ``/api/plugins/{name}`` (API process),
+- forwards §8.3 events to plugin hooks (both API and worker processes),
+- aggregates UI manifests for ``GET /api/plugins/ui-manifest``.
+
+Plugin background jobs (§11.2) and migrations (§11.1) are wired in later M3 phases.
+"""
+
+from __future__ import annotations
+
+import logging
+from importlib.metadata import entry_points
+from typing import TYPE_CHECKING, Any
+
+from app.events import EventBus
+from app.plugins.types import Page, Plugin, Slot, UiManifest
+
+if TYPE_CHECKING:
+    from fastapi import FastAPI
+
+logger = logging.getLogger(__name__)
+
+ENTRYPOINT_GROUP = "webmail.plugins"
+
+_plugins: list[Plugin] | None = None
+# Plugin names whose hooks are already subscribed on a given bus, so repeated
+# create_app()/worker starts in one process don't double-register (tests, reload).
+_hooks_registered: set[tuple[int, str]] = set()
+
+
+def _coerce_plugin(obj: Any) -> Plugin:
+    """An entry point may resolve to a ``Plugin`` or a module exposing ``plugin``."""
+    if isinstance(obj, Plugin):
+        return obj
+    candidate = getattr(obj, "plugin", None)
+    if isinstance(candidate, Plugin):
+        return candidate
+    raise TypeError(f"entry point {obj!r} does not expose a Plugin (SPEC §11)")
+
+
+def discover_plugins() -> list[Plugin]:
+    """Load every plugin registered under the ``webmail.plugins`` group."""
+    found: list[Plugin] = []
+    seen: set[str] = set()
+    for ep in entry_points(group=ENTRYPOINT_GROUP):
+        try:
+            plugin = _coerce_plugin(ep.load())
+        except Exception:  # noqa: BLE001 - one bad plugin must not break the app
+            logger.exception("failed to load plugin entry point %s", ep.name)
+            continue
+        if plugin.name in seen:
+            logger.error("duplicate plugin name %r; skipping", plugin.name)
+            continue
+        seen.add(plugin.name)
+        found.append(plugin)
+        logger.info("loaded plugin %s v%s", plugin.name, plugin.version)
+    return found
+
+
+def get_plugins() -> list[Plugin]:
+    """Return the process-wide discovered plugin list (cached)."""
+    global _plugins
+    if _plugins is None:
+        _plugins = discover_plugins()
+    return _plugins
+
+
+def set_plugins_for_test(plugins: list[Plugin] | None) -> None:
+    """Override (or reset with ``None``) the plugin registry — tests only."""
+    global _plugins
+    _plugins = plugins
+    _hooks_registered.clear()
+
+
+def register_hooks(bus: EventBus) -> None:
+    """Subscribe each plugin's hooks to the bus (idempotent per process/bus).
+
+    Called in both the API and the worker so hooks fire wherever the event is
+    published (e.g. ``message.new`` originates in the worker)."""
+    for plugin in get_plugins():
+        marker = (id(bus), plugin.name)
+        if marker in _hooks_registered:
+            continue
+        for event, handler in plugin.hooks.items():
+            bus.subscribe(event, handler)
+        _hooks_registered.add(marker)
+
+
+def mount_routers(app: FastAPI) -> None:
+    """Mount each plugin's router at ``/api/plugins/{name}`` (SPEC §11)."""
+    for plugin in get_plugins():
+        if plugin.router is not None:
+            app.include_router(plugin.router, prefix=f"/api/plugins/{plugin.name}")
+
+
+def _slot_dict(slot: Slot) -> dict[str, str]:
+    return {"name": slot.name, "bundle": slot.bundle}
+
+
+def _page_dict(page: Page) -> dict[str, Any]:
+    return {
+        "route": page.route,
+        "bundle": page.bundle,
+        "nav": {"icon": page.nav.icon, "label": page.nav.label, "order": page.nav.order},
+    }
+
+
+def _manifest_dict(plugin: Plugin, manifest: UiManifest) -> dict[str, Any]:
+    return {
+        "name": plugin.name,
+        "version": plugin.version,
+        "builtin": plugin.builtin,  # core plugins the UI must not offer to remove
+        "slots": [_slot_dict(s) for s in manifest.slots],
+        "pages": [_page_dict(p) for p in manifest.pages],
+        "capabilities": dict(manifest.capabilities),
+    }
+
+
+def build_ui_manifest() -> dict[str, Any]:
+    """Aggregate every plugin's UI manifest for the frontend loader (SPEC §11.3)."""
+    plugins = [
+        _manifest_dict(p, p.ui_manifest) for p in get_plugins() if p.ui_manifest is not None
+    ]
+    return {"plugins": plugins}
+
+
+def get_plugin(name: str) -> Plugin | None:
+    """Return the loaded plugin named ``name``, or None."""
+    return next((p for p in get_plugins() if p.name == name), None)
+
+
+class PluginRemovalError(Exception):
+    """Raised when trying to uninstall a builtin (core) plugin (SPEC §11 / §12)."""
+
+
+def assert_removable(name: str) -> Plugin:
+    """Return the plugin, or raise if it's unknown or builtin (non-removable).
+
+    Core plugins (calendar, contacts) ship ``builtin=True`` and may never be
+    uninstalled by a user; the uninstall path calls this before touching data."""
+    plugin = get_plugin(name)
+    if plugin is None:
+        raise PluginRemovalError(f"unknown plugin {name!r}")
+    if plugin.builtin:
+        raise PluginRemovalError(f"plugin {name!r} is builtin and cannot be removed")
+    return plugin
diff --git a/backend/app/plugins/migrate.py b/backend/app/plugins/migrate.py
new file mode 100644
index 0000000..dcf6ed1
--- /dev/null
+++ b/backend/app/plugins/migrate.py
@@ -0,0 +1,98 @@
+"""Per-plugin Alembic migration runner + install/uninstall lifecycle (SPEC §11.1).
+
+Each plugin ships its own revision directory (``Plugin.migrations``) and runs
+against a dedicated version table, so its schema history is independent of core
+and of other plugins. ``install`` upgrades to head; ``uninstall --drop-data``
+runs the plugin's downgrade chain and removes the version table, leaving zero
+residue (the §12 M3 acceptance round-trip). Builtin (core) plugins refuse removal.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+from pathlib import Path
+
+from alembic import command
+from alembic.config import Config
+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
+from app.plugins.types import Plugin
+
+logger = logging.getLogger(__name__)
+
+_SHARED_ENV = str(Path(__file__).parent / "alembic")
+
+
+class PluginMigrationError(Exception):
+    """Raised when a plugin's migrations can't be run."""
+
+
+def _version_table(plugin: Plugin) -> str:
+    # plugin.name is validated [a-z][a-z0-9_]* at construction, so this is safe to
+    # interpolate into DDL.
+    return f"alembic_version_plg_{plugin.name}"
+
+
+def _config(plugin: Plugin) -> Config:
+    if not plugin.migrations:
+        raise PluginMigrationError(f"plugin {plugin.name!r} declares no migrations")
+    cfg = Config()
+    cfg.set_main_option("script_location", _SHARED_ENV)
+    cfg.set_main_option("version_locations", plugin.migrations)
+    cfg.set_main_option("path_separator", "os")  # split version_locations on os.pathsep only
+    cfg.set_main_option("version_table", _version_table(plugin))
+    return cfg
+
+
+def upgrade(plugin: Plugin, revision: str = "head") -> None:
+    """Run the plugin's migrations up to ``revision`` (default: head)."""
+    command.upgrade(_config(plugin), revision)
+
+
+def downgrade(plugin: Plugin, revision: str = "base") -> None:
+    """Run the plugin's downgrades to ``revision`` (default: base = drop all)."""
+    command.downgrade(_config(plugin), revision)
+
+
+async def _drop_version_table(plugin: Plugin) -> None:
+    # Fresh engine (not the shared global one) so this is safe to call from any loop.
+    engine = create_async_engine(get_settings().database_url, poolclass=NullPool)
+    try:
+        async with engine.begin() as conn:
+            await conn.execute(text(f"DROP TABLE IF EXISTS {_version_table(plugin)}"))
+    finally:
+        await engine.dispose()
+
+
+def install(name: str) -> None:
+    """Apply a plugin's migrations (create its ``plg_*`` tables). No-op if none."""
+    plugin = loader.get_plugin(name)
+    if plugin is None:
+        raise PluginMigrationError(f"unknown plugin {name!r}")
+    if plugin.migrations is None:
+        logger.info("plugin %s has no migrations; nothing to install", name)
+        return
+    logger.info("installing plugin %s: upgrade -> head", name)
+    upgrade(plugin, "head")
+
+
+def uninstall(name: str, *, drop_data: bool = False) -> None:
+    """Uninstall a plugin. Refuses builtin plugins.
+
+    Without ``drop_data`` the schema/data are kept (a reversible disable). With
+    ``drop_data`` the downgrade chain runs and the version table is removed, so
+    nothing remains in the database (SPEC §12 M3 acceptance)."""
+    plugin = loader.assert_removable(name)  # raises PluginRemovalError for builtin/unknown
+    if not drop_data:
+        logger.info("uninstalling plugin %s (data kept)", name)
+        return
+    if plugin.migrations is None:
+        return
+    logger.info("uninstalling plugin %s --drop-data: downgrade -> base", name)
+    downgrade(plugin, "base")
+    asyncio.run(_drop_version_table(plugin))
diff --git a/backend/app/plugins/rls.py b/backend/app/plugins/rls.py
new file mode 100644
index 0000000..0156b90
--- /dev/null
+++ b/backend/app/plugins/rls.py
@@ -0,0 +1,46 @@
+"""Row-Level Security for plugin-owned tables (SPEC §11.1 + privacy hardening).
+
+Per-user isolation for ``plg_*`` tables is enforced by Postgres, not by remembering
+a ``WHERE user_id = ?`` in every query. Each user-data table gets RLS enabled +
+forced, with a policy comparing ``user_id`` to the transaction-local GUC
+``app.current_user_id``. Plugin code reaches these tables only through
+``sdk.session(user_id)`` (see :mod:`app.plugins.db`), which drops to the
+least-privilege :data:`PLUGIN_ROLE` and binds that GUC — so even a query that
+forgets to filter cannot see or write another user's rows.
+
+Plugin migrations call :func:`enable_rls` right after creating a user-data table.
+"""
+
+from __future__ import annotations
+
+# NOLOGIN, non-superuser, NOBYPASSRLS role plugin sessions SET LOCAL ROLE into
+# (created by core migration 0014). RLS is skipped for superusers / table owners /
+# BYPASSRLS roles, so plugin access must run as this restricted role to be enforced.
+PLUGIN_ROLE = "webmail_plugin"
+
+_USER_CTX = "current_setting('app.current_user_id', true)::uuid"
+
+
+def rls_ddl(table: str, *, user_column: str = "user_id") -> list[str]:
+    """SQL statements that lock ``table`` to the current user (SPEC §11.1).
+
+    Pure/testable: returns the DDL rather than executing it. ``FORCE`` makes even
+    the table owner subject to the policy; ``WITH CHECK`` blocks inserting/updating
+    rows for a different user."""
+    policy = f"{table}_user_isolation"
+    return [
+        f"ALTER TABLE {table} ENABLE ROW LEVEL SECURITY",
+        f"ALTER TABLE {table} FORCE ROW LEVEL SECURITY",
+        f"CREATE POLICY {policy} ON {table} "
+        f"USING ({user_column} = {_USER_CTX}) "
+        f"WITH CHECK ({user_column} = {_USER_CTX})",
+        f"GRANT SELECT, INSERT, UPDATE, DELETE ON {table} TO {PLUGIN_ROLE}",
+    ]
+
+
+def enable_rls(table: str, *, user_column: str = "user_id") -> None:
+    """Apply :func:`rls_ddl` via Alembic ``op`` — call from a plugin migration."""
+    from alembic import op
+
+    for statement in rls_ddl(table, user_column=user_column):
+        op.execute(statement)
diff --git a/backend/app/plugins/sdk.py b/backend/app/plugins/sdk.py
new file mode 100644
index 0000000..e96e06c
--- /dev/null
+++ b/backend/app/plugins/sdk.py
@@ -0,0 +1,116 @@
+"""The plugin SDK — the ONLY ``app.*`` surface a plugin may import (SPEC §11).
+
+Everything a plugin needs is reached through :func:`sdk`, which returns a
+:class:`PluginSdk` bound to the plugin's name: a plugin-scoped DB session, the
+event bus (publishing under ``plugin.{name}.*``), the blob store, outbox
+draft/send helpers, the settings accessor, an SSRF-guarded HTTP client
+(§10.6), and the namespaced KV store (§11).
+
+The frozen contract types (:class:`Plugin`, :class:`UiManifest`, :class:`JobSpec`,
+…) are re-exported here so plugin packages import only from ``app.plugins.sdk``.
+"""
+
+from __future__ import annotations
+
+import uuid
+from contextlib import AbstractAsyncContextManager
+from dataclasses import dataclass
+from typing import Any
+
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.accounts.ssrf import guarded_get
+from app.config import Settings, get_settings
+from app.events import get_event_bus
+from app.indexer import blobstore
+from app.outbox import service as outbox_service
+from app.plugins.db import plugin_session
+from app.plugins.kv import PluginKvStore
+from app.plugins.types import (
+    Hook,
+    JobFunc,
+    JobSpec,
+    Page,
+    PageNav,
+    Plugin,
+    Slot,
+    UiManifest,
+)
+from app.queue import enqueue_job
+
+__all__ = [
+    "Hook",
+    "JobFunc",
+    "JobSpec",
+    "Page",
+    "PageNav",
+    "Plugin",
+    "PluginSdk",
+    "Slot",
+    "UiManifest",
+    "blobstore",
+    "sdk",
+]
+
+
+@dataclass(frozen=True)
+class PluginSdk:
+    """A lightweight facade over shared services, scoped to one plugin.
+
+    Cheap to construct (wraps process-wide singletons + the plugin name), so
+    handlers/routes obtain it on demand via ``sdk("<name>")``."""
+
+    name: str
+
+    # --- config -------------------------------------------------------------
+    @property
+    def settings(self) -> Settings:
+        return get_settings()
+
+    # --- database -----------------------------------------------------------
+    def session(self, user_id: uuid.UUID) -> AbstractAsyncContextManager[AsyncSession]:
+        """An RLS-enforced transactional session scoped to ``user_id`` (SPEC §11.1).
+
+        Row-level security limits every query to this user's rows on ``plg_*``
+        tables — even a query that forgets ``WHERE user_id`` cannot leak or write
+        across users (see :mod:`app.plugins.db`)."""
+        return plugin_session(user_id)
+
+    def kv(self, user_id: uuid.UUID) -> PluginKvStore:
+        """The namespaced KV store for this plugin and ``user_id`` (SPEC §11)."""
+        return PluginKvStore(self.name, user_id)
+
+    # --- events -------------------------------------------------------------
+    async def publish(self, event: str, payload: dict[str, object]) -> None:
+        """Publish ``plugin.{name}.{event}`` on the bus (payload needs ``user_id``)."""
+        await get_event_bus().publish(f"plugin.{self.name}.{event}", payload)
+
+    # --- background jobs ----------------------------------------------------
+    async def enqueue(self, job_func: JobFunc, **kwargs: Any) -> None:
+        """Enqueue one of this plugin's jobs on the shared worker (SPEC §11.2).
+
+        ``job_func`` must be a job declared in this plugin's ``jobs=[...]``. Pass
+        ``user_id=`` for singleton jobs so the per-user lock applies."""
+        await enqueue_job(f"plg.{self.name}.{job_func.__name__}", **kwargs)
+
+    # --- blob store ---------------------------------------------------------
+    @property
+    def blob(self) -> object:
+        """The blob store (``store``/``load``/``exists``/``remove``), keyed by user."""
+        return blobstore
+
+    # --- outbox -------------------------------------------------------------
+    @property
+    def outbox(self) -> object:
+        """Draft/send helpers (``upsert_draft``, ``create_outbox``, …)."""
+        return outbox_service
+
+    # --- outbound HTTP ------------------------------------------------------
+    async def http_get(self, url: str) -> str | None:
+        """GET ``url`` through the §10.6 SSRF guard (blocks private IPs/oversize)."""
+        return await guarded_get(url)
+
+
+def sdk(name: str) -> PluginSdk:
+    """Return the SDK facade bound to plugin ``name`` (SPEC §11)."""
+    return PluginSdk(name)
diff --git a/backend/app/plugins/types.py b/backend/app/plugins/types.py
new file mode 100644
index 0000000..b27ae83
--- /dev/null
+++ b/backend/app/plugins/types.py
@@ -0,0 +1,106 @@
+# INTERFACE VERSION: 1
+"""Frozen plugin contract types (SPEC §11).
+
+A plugin is a Python package ``webmail_plugin_<name>`` exposing a module-level
+``plugin = Plugin(...)``, discovered via the ``webmail.plugins`` entry-point group.
+
+These dataclasses are the frozen surface (SPEC §11 "freeze in M3"): fields may be
+added with defaults, but existing names/meanings may not change without bumping
+the INTERFACE VERSION above.
+"""
+
+from __future__ import annotations
+
+import re
+from collections.abc import Awaitable, Callable
+from dataclasses import dataclass, field
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    from fastapi import APIRouter
+
+# A hook handler receives an event payload (always carrying ``user_id``, SPEC §5.3).
+Hook = Callable[[dict[str, object]], Awaitable[None]]
+# A background job body: receives the arq context dict plus job-specific kwargs.
+JobFunc = Callable[..., Awaitable[Any]]
+
+# The frozen slot catalog (SPEC §11.3). Bundles are injected into these UI points.
+SLOT_NAMES: frozenset[str] = frozenset(
+    {"thread.toolbar", "message.actions", "message.banner", "sidebar.section", "settings.page"}
+)
+
+_NAME_RE = re.compile(r"[a-z][a-z0-9_]*")
+
+
+@dataclass(frozen=True)
+class Slot:
+    """A lazy-loaded ESM bundle injected into a named mail-UI slot (SPEC §11.3)."""
+
+    name: str
+    bundle: str  # path served by the plugin router, resolved by the frontend loader
+
+    def __post_init__(self) -> None:
+        if self.name not in SLOT_NAMES:
+            raise ValueError(f"unknown slot {self.name!r} (SPEC §11.3 slot catalog)")
+
+
+@dataclass(frozen=True)
+class PageNav:
+    """Nav entry for a page-plugin (SPEC §11.3)."""
+
+    icon: str
+    label: str
+    order: int = 100
+
+
+@dataclass(frozen=True)
+class Page:
+    """A full-content-area view mounted at ``route`` with a nav entry (SPEC §11.3)."""
+
+    route: str
+    nav: PageNav
+    bundle: str
+
+
+@dataclass(frozen=True)
+class UiManifest:
+    """A plugin's declared frontend surfaces (SPEC §11.3)."""
+
+    slots: list[Slot] = field(default_factory=list)
+    pages: list[Page] = field(default_factory=list)
+    capabilities: dict[str, str] = field(default_factory=dict)  # name -> endpoint path
+
+
+@dataclass(frozen=True)
+class JobSpec:
+    """A background task on the shared arq worker (SPEC §11.2).
+
+    ``schedule`` is a cron string for periodic jobs (None = enqueue on demand);
+    ``singleton`` caps it to one running instance per (plugin, user) via a Redis
+    lock. Registration onto the worker is done by the loader (M3 §11.2)."""
+
+    func: JobFunc
+    schedule: str | None = None
+    singleton: bool = False
+
+
+@dataclass(frozen=True)
+class Plugin:
+    """The object a plugin package exposes as module-level ``plugin`` (SPEC §11)."""
+
+    name: str
+    version: str
+    hooks: dict[str, Hook] = field(default_factory=dict)
+    router: APIRouter | None = None
+    ui_manifest: UiManifest | None = None
+    migrations: str | None = None  # path to the plugin's Alembic version branch (11.1)
+    jobs: list[JobSpec] = field(default_factory=list)
+    # Core plugins (calendar, contacts) ship builtin=True: always installed, never
+    # offered for removal in the UI, and the uninstall path refuses --drop-data.
+    builtin: bool = False
+
+    def __post_init__(self) -> None:
+        if not _NAME_RE.fullmatch(self.name):
+            raise ValueError(
+                f"invalid plugin name {self.name!r}: must match [a-z][a-z0-9_]* (SPEC §11)"
+            )
diff --git a/backend/migrations/versions/0013_plugin_kv.py b/backend/migrations/versions/0013_plugin_kv.py
new file mode 100644
index 0000000..4046a29
--- /dev/null
+++ b/backend/migrations/versions/0013_plugin_kv.py
@@ -0,0 +1,39 @@
+"""add plugin_kv (SPEC §11 plugin namespaced key/value store)
+
+Core-owned table backing ``plugin_kv(plugin, user_id, key)`` — the light-state
+store every plugin gets (SPEC §11). Not a ``plg_``-prefixed plugin-owned table;
+plugin-owned tables ship in each plugin's own Alembic branch (§11.1).
+
+Revision ID: 0013
+Revises: 0012
+Create Date: 2026-07-26
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+from alembic import op
+
+revision: str = "0013"
+down_revision: str | None = "0012"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.execute(
+        """
+        CREATE TABLE plugin_kv (
+            plugin  text NOT NULL,
+            user_id uuid NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+            key     text NOT NULL,
+            value   jsonb NOT NULL,
+            PRIMARY KEY (plugin, user_id, key)
+        )
+        """
+    )
+
+
+def downgrade() -> None:
+    op.execute("DROP TABLE IF EXISTS plugin_kv")
diff --git a/backend/migrations/versions/0014_plugin_role.py b/backend/migrations/versions/0014_plugin_role.py
new file mode 100644
index 0000000..dda3e4e
--- /dev/null
+++ b/backend/migrations/versions/0014_plugin_role.py
@@ -0,0 +1,61 @@
+"""create the least-privilege plugin DB role (SPEC §11.1 RLS enforcement)
+
+Plugin table access runs as ``webmail_plugin`` — a NOLOGIN, NOSUPERUSER,
+NOBYPASSRLS role that plugin sessions ``SET LOCAL ROLE`` into per transaction.
+Row-Level Security is skipped for superusers, table owners, and BYPASSRLS roles,
+so per-user isolation on ``plg_*`` tables is only real when access runs as this
+restricted role. The app role is granted membership so it can SET ROLE into it
+(the dev role happens to be superuser, but this keeps prod parity where it isn't).
+
+Per-table SELECT/INSERT/UPDATE/DELETE grants + policies are added by each plugin's
+own migration via ``app.plugins.rls.enable_rls`` (§11.1); this only provisions the
+role and schema usage.
+
+Revision ID: 0014
+Revises: 0013
+Create Date: 2026-07-26
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+from alembic import op
+
+revision: str = "0014"
+down_revision: str | None = "0013"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.execute(
+        """
+        DO $$
+        BEGIN
+            IF NOT EXISTS (SELECT 1 FROM pg_roles WHERE rolname = 'webmail_plugin') THEN
+                CREATE ROLE webmail_plugin NOLOGIN NOSUPERUSER NOBYPASSRLS NOCREATEDB NOCREATEROLE;
+            END IF;
+        END
+        $$;
+        """
+    )
+    op.execute("GRANT USAGE ON SCHEMA public TO webmail_plugin")
+    # Let the connecting application role drop into the restricted role via SET ROLE.
+    op.execute("GRANT webmail_plugin TO CURRENT_USER")
+
+
+def downgrade() -> None:
+    op.execute(
+        """
+        DO $$
+        BEGIN
+            IF EXISTS (SELECT 1 FROM pg_roles WHERE rolname = 'webmail_plugin') THEN
+                EXECUTE 'REVOKE webmail_plugin FROM CURRENT_USER';
+                EXECUTE 'DROP OWNED BY webmail_plugin';
+                EXECUTE 'DROP ROLE webmail_plugin';
+            END IF;
+        END
+        $$;
+        """
+    )
diff --git a/backend/tests/fixtures/plugin_demo/versions/0001_note.py b/backend/tests/fixtures/plugin_demo/versions/0001_note.py
new file mode 100644
index 0000000..f4c70b9
--- /dev/null
+++ b/backend/tests/fixtures/plugin_demo/versions/0001_note.py
@@ -0,0 +1,35 @@
+"""demo plugin: a user-owned note table with RLS (skeleton for SPEC §11.1 tests)
+
+Revision ID: demo0001
+Revises:
+Create Date: 2026-07-26
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+from alembic import op
+
+from app.plugins.rls import enable_rls
+
+revision: str = "demo0001"
+down_revision: str | None = None
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.execute(
+        "CREATE TABLE plg_demo_note ("
+        "id uuid PRIMARY KEY DEFAULT gen_random_uuid(), "
+        "user_id uuid NOT NULL, "
+        "body text NOT NULL DEFAULT '')"
+    )
+    # Per-user isolation enforced by Postgres (SPEC §11.1); every plg_ user-data
+    # table calls this right after creation.
+    enable_rls("plg_demo_note")
+
+
+def downgrade() -> None:
+    op.execute("DROP TABLE IF EXISTS plg_demo_note")
diff --git a/backend/tests/plugins/__init__.py b/backend/tests/plugins/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/backend/tests/plugins/conftest.py b/backend/tests/plugins/conftest.py
new file mode 100644
index 0000000..040c697
--- /dev/null
+++ b/backend/tests/plugins/conftest.py
@@ -0,0 +1,16 @@
+"""Reset the plugin registry after each test so a test override never leaks into
+other suites that call ``create_app`` (which mounts discovered plugins)."""
+
+from __future__ import annotations
+
+from collections.abc import Iterator
+
+import pytest
+
+from app.plugins import loader
+
+
+@pytest.fixture(autouse=True)
+def _reset_plugins() -> Iterator[None]:
+    yield
+    loader.set_plugins_for_test(None)
diff --git a/backend/tests/plugins/test_builtin.py b/backend/tests/plugins/test_builtin.py
new file mode 100644
index 0000000..325d8ec
--- /dev/null
+++ b/backend/tests/plugins/test_builtin.py
@@ -0,0 +1,38 @@
+"""Builtin (non-removable core) plugin handling (SPEC §11 / §12)."""
+
+from __future__ import annotations
+
+import pytest
+
+from app.plugins import loader
+from app.plugins.sdk import Plugin
+
+
+def test_builtin_defaults_false() -> None:
+    assert Plugin(name="filters", version="1").builtin is False
+    assert Plugin(name="calendar", version="1", builtin=True).builtin is True
+
+
+def test_assert_removable_blocks_builtin() -> None:
+    loader.set_plugins_for_test(
+        [
+            Plugin(name="filters", version="1"),  # removable
+            Plugin(name="calendar", version="1", builtin=True),  # core, non-removable
+        ]
+    )
+    assert loader.assert_removable("filters").name == "filters"
+
+    with pytest.raises(loader.PluginRemovalError, match="builtin"):
+        loader.assert_removable("calendar")
+    with pytest.raises(loader.PluginRemovalError, match="unknown"):
+        loader.assert_removable("nope")
+
+
+def test_builtin_surfaces_in_ui_manifest() -> None:
+    from app.plugins.sdk import UiManifest
+
+    loader.set_plugins_for_test(
+        [Plugin(name="calendar", version="1", builtin=True, ui_manifest=UiManifest())]
+    )
+    entry = loader.build_ui_manifest()["plugins"][0]
+    assert entry["name"] == "calendar" and entry["builtin"] is True
diff --git a/backend/tests/plugins/test_jobs.py b/backend/tests/plugins/test_jobs.py
new file mode 100644
index 0000000..e231430
--- /dev/null
+++ b/backend/tests/plugins/test_jobs.py
@@ -0,0 +1,115 @@
+"""Plugin background jobs: registration, cron parsing, singleton lock (SPEC §11.2)."""
+
+from __future__ import annotations
+
+from typing import Any
+
+import pytest
+
+from app.plugins import jobs, loader
+from app.plugins.jobs import job_name, parse_cron, plugin_arq_functions, plugin_cron_jobs
+from app.plugins.sdk import JobSpec, Plugin, sdk
+from app.redis_client import get_redis
+
+
+async def _noop(ctx: dict[str, Any], **kwargs: Any) -> None:
+    return None
+
+
+def test_job_name_is_namespaced() -> None:
+    assert job_name("calendar", JobSpec(func=_noop)) == "plg.calendar._noop"
+
+
+def test_parse_cron() -> None:
+    assert parse_cron("*/15 * * * *") == {
+        "minute": {0, 15, 30, 45},
+        "hour": None,
+        "day": None,
+        "month": None,
+        "weekday": None,
+    }
+    assert parse_cron("0 9-11 1 * 1,3") == {
+        "minute": {0},
+        "hour": {9, 10, 11},
+        "day": {1},
+        "month": None,
+        "weekday": {1, 3},
+    }
+    with pytest.raises(ValueError, match="5 fields"):
+        parse_cron("* * *")
+
+
+def test_functions_and_cron_registered() -> None:
+    async def refresh(ctx: dict[str, Any], **kwargs: Any) -> None:
+        return None
+
+    async def poll(ctx: dict[str, Any], **kwargs: Any) -> None:
+        return None
+
+    loader.set_plugins_for_test(
+        [
+            Plugin(
+                name="cal",
+                version="1",
+                jobs=[JobSpec(func=refresh), JobSpec(func=poll, schedule="*/5 * * * *")],
+            )
+        ]
+    )
+    fn_names = {f.name for f in plugin_arq_functions()}
+    assert fn_names == {"plg.cal.refresh", "plg.cal.poll"}  # both enqueueable
+
+    crons = plugin_cron_jobs()
+    assert [c.name for c in crons] == ["plg.cal.poll.cron"]  # only the scheduled one
+
+
+async def test_singleton_lock_prevents_overlap() -> None:
+    calls: list[str] = []
+
+    async def work(ctx: dict[str, Any], **kwargs: Any) -> None:
+        calls.append(str(kwargs.get("user_id")))
+
+    plugin = Plugin(name="cal", version="1", jobs=[JobSpec(func=work, singleton=True)])
+    runner, _ = jobs._make_runner(plugin, plugin.jobs[0])
+
+    await runner({}, user_id="u1")  # runs; lock acquired then released
+    assert calls == ["u1"]
+
+    # Simulate an instance already holding the lock for u2 -> the run is skipped.
+    held = jobs._lock_key("cal", "work", "u2")
+    await get_redis().set(held, b"1", nx=True, ex=60)
+    await runner({}, user_id="u2")
+    assert calls == ["u1"]  # unchanged
+
+    await get_redis().delete(held)
+    await runner({}, user_id="u2")  # lock free now -> runs
+    assert calls == ["u1", "u2"]
+
+
+async def test_non_singleton_always_runs() -> None:
+    calls: list[int] = []
+
+    async def work(ctx: dict[str, Any], **kwargs: Any) -> None:
+        calls.append(1)
+
+    plugin = Plugin(name="cal", version="1", jobs=[JobSpec(func=work)])
+    runner, _ = jobs._make_runner(plugin, plugin.jobs[0])
+    await runner({}, user_id="u1")
+    await runner({}, user_id="u1")
+    assert calls == [1, 1]  # no lock, both run
+
+
+async def test_sdk_enqueue_uses_namespaced_name(monkeypatch: pytest.MonkeyPatch) -> None:
+    captured: dict[str, Any] = {}
+
+    async def fake_enqueue(name: str, **kwargs: Any) -> None:
+        captured["name"] = name
+        captured["kwargs"] = kwargs
+
+    monkeypatch.setattr("app.plugins.sdk.enqueue_job", fake_enqueue)
+
+    async def refresh(ctx: dict[str, Any], **kwargs: Any) -> None:
+        return None
+
+    await sdk("cal").enqueue(refresh, user_id="u1")
+    assert captured["name"] == "plg.cal.refresh"
+    assert captured["kwargs"] == {"user_id": "u1"}
diff --git a/backend/tests/plugins/test_kv.py b/backend/tests/plugins/test_kv.py
new file mode 100644
index 0000000..bf4a53e
--- /dev/null
+++ b/backend/tests/plugins/test_kv.py
@@ -0,0 +1,52 @@
+"""Namespaced plugin KV store round-trips (SPEC §11 plugin_kv)."""
+
+from __future__ import annotations
+
+import uuid
+
+from sqlalchemy import delete
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import get_settings
+from app.db import session_scope
+from app.identity.passwords import hash_password
+from app.models import User
+from app.plugins.sdk import sdk
+
+
+async def test_plugin_kv_crud_is_namespaced() -> None:
+    engine = create_async_engine(get_settings().database_url, poolclass=NullPool)
+    sm = async_sessionmaker(engine, expire_on_commit=False)
+    session = sm()
+    user = User(handle=f"kv{uuid.uuid4().hex[:8]}@test.local", password_hash=hash_password("pw"))
+    session.add(user)
+    await session.commit()
+
+    try:
+        kv = sdk("filters").kv(user.id)
+        other = sdk("labels").kv(user.id)  # different plugin, same user
+
+        assert await kv.get("rules", default=[]) == []  # missing key -> default
+        await kv.set("rules", [{"match": "boss", "flag": "important"}])
+        await kv.set("count", 3)
+        assert await kv.get("rules") == [{"match": "boss", "flag": "important"}]
+        assert await kv.get("count") == 3
+
+        # Namespacing: the labels plugin sees nothing filters wrote.
+        assert await other.get("rules") is None
+        assert await other.items() == {}
+
+        assert await kv.items() == {"rules": [{"match": "boss", "flag": "important"}], "count": 3}
+
+        await kv.set("count", 4)  # upsert overwrites
+        assert await kv.get("count") == 4
+
+        await kv.delete("count")
+        assert await kv.get("count") is None
+        assert set((await kv.items()).keys()) == {"rules"}
+    finally:
+        async with session_scope() as cleanup:  # cascade drops plugin_kv rows
+            await cleanup.execute(delete(User).where(User.id == user.id))
+        await session.close()
+        await engine.dispose()
diff --git a/backend/tests/plugins/test_loader.py b/backend/tests/plugins/test_loader.py
new file mode 100644
index 0000000..a50e0e8
--- /dev/null
+++ b/backend/tests/plugins/test_loader.py
@@ -0,0 +1,117 @@
+"""Plugin discovery + core wiring (SPEC §11)."""
+
+from __future__ import annotations
+
+import httpx
+import pytest
+from fastapi import APIRouter, FastAPI
+from httpx import ASGITransport
+
+from app.events import get_event_bus
+from app.plugins import loader
+from app.plugins.sdk import Page, PageNav, Plugin, Slot, UiManifest
+
+
+class _FakeEP:
+    def __init__(self, name: str, obj: object) -> None:
+        self.name = name
+        self._obj = obj
+
+    def load(self) -> object:
+        return self._obj
+
+
+def test_discover_reads_entry_points(monkeypatch: pytest.MonkeyPatch) -> None:
+    plugin = Plugin(name="filters", version="1.2")
+    monkeypatch.setattr(loader, "entry_points", lambda group: [_FakeEP("filters", plugin)])
+    loader.set_plugins_for_test(None)  # force rediscovery through the fake
+    found = loader.discover_plugins()
+    assert [(p.name, p.version) for p in found] == [("filters", "1.2")]
+
+
+def test_discover_accepts_module_exposing_plugin(monkeypatch: pytest.MonkeyPatch) -> None:
+    class _Mod:
+        plugin = Plugin(name="labels", version="0.1")
+
+    monkeypatch.setattr(loader, "entry_points", lambda group: [_FakeEP("labels", _Mod())])
+    loader.set_plugins_for_test(None)
+    assert [p.name for p in loader.discover_plugins()] == ["labels"]
+
+
+def test_discover_skips_duplicate_names(monkeypatch: pytest.MonkeyPatch) -> None:
+    eps = [
+        _FakeEP("a", Plugin(name="dup", version="1")),
+        _FakeEP("b", Plugin(name="dup", version="2")),
+    ]
+    monkeypatch.setattr(loader, "entry_points", lambda group: eps)
+    loader.set_plugins_for_test(None)
+    found = loader.discover_plugins()
+    assert [p.version for p in found] == ["1"]  # first wins, duplicate dropped
+
+
+async def test_register_hooks_forwards_events() -> None:
+    seen: list[dict[str, object]] = []
+
+    async def on_new(payload: dict[str, object]) -> None:
+        seen.append(payload)
+
+    loader.set_plugins_for_test(
+        [Plugin(name="watcher", version="1", hooks={"message.new": on_new})]
+    )
+    bus = get_event_bus()
+    loader.register_hooks(bus)
+    loader.register_hooks(bus)  # idempotent: no double subscription
+
+    await bus.publish("message.new", {"user_id": "u", "message_id": "m"})
+    assert seen == [{"user_id": "u", "message_id": "m"}]
+
+
+async def test_mount_routers_prefixes_by_name() -> None:
+    r = APIRouter()
+
+    @r.get("/ping")
+    async def _ping() -> dict[str, str]:
+        return {"ok": "1"}
+
+    loader.set_plugins_for_test([Plugin(name="demo", version="1", router=r)])
+    app = FastAPI()
+    loader.mount_routers(app)
+    transport = ASGITransport(app=app)
+    async with httpx.AsyncClient(transport=transport, base_url="http://testserver") as client:
+        resp = await client.get("/api/plugins/demo/ping")
+    assert resp.status_code == 200
+    assert resp.json() == {"ok": "1"}
+
+
+def test_build_ui_manifest_aggregates() -> None:
+    manifest = UiManifest(
+        slots=[Slot(name="message.actions", bundle="/a.js")],
+        pages=[
+            Page(
+                route="/notes",
+                nav=PageNav(icon="note", label="Notes", order=5),
+                bundle="/p.js",
+            )
+        ],
+        capabilities={"recipients.suggest": "/api/plugins/contacts/suggest"},
+    )
+    loader.set_plugins_for_test([Plugin(name="notes", version="2.0", ui_manifest=manifest)])
+    out = loader.build_ui_manifest()
+    assert out == {
+        "plugins": [
+            {
+                "name": "notes",
+                "version": "2.0",
+                "builtin": False,
+                "slots": [{"name": "message.actions", "bundle": "/a.js"}],
+                "pages": [
+                    {
+                        "route": "/notes",
+                        "bundle": "/p.js",
+                        "nav": {"icon": "note", "label": "Notes", "order": 5},
+                    }
+                ],
+                "capabilities": {"recipients.suggest": "/api/plugins/contacts/suggest"},
+            }
+        ]
+    }
diff --git a/backend/tests/plugins/test_migrate.py b/backend/tests/plugins/test_migrate.py
new file mode 100644
index 0000000..4c5c359
--- /dev/null
+++ b/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")
diff --git a/backend/tests/plugins/test_rls.py b/backend/tests/plugins/test_rls.py
new file mode 100644
index 0000000..2a97b19
--- /dev/null
+++ b/backend/tests/plugins/test_rls.py
@@ -0,0 +1,84 @@
+"""Row-Level Security enforcement for plugin tables (SPEC §11.1 + privacy).
+
+Proves that per-user isolation is enforced by Postgres — not by the query — so a
+plugin that forgets ``WHERE user_id`` still cannot read or write another user's
+rows. Requires the ``webmail_plugin`` role (migration 0014) to be applied.
+"""
+
+from __future__ import annotations
+
+import uuid
+
+import pytest
+from sqlalchemy import text
+
+from app.db import session_scope
+from app.plugins.db import plugin_session
+from app.plugins.rls import rls_ddl
+from app.plugins.sdk import sdk
+
+TABLE = "plg_rlsdemo_note"
+
+
+async def _create_demo_table() -> None:
+    async with session_scope() as s:
+        await s.execute(text(f"DROP TABLE IF EXISTS {TABLE}"))
+        await s.execute(
+            text(
+                f"CREATE TABLE {TABLE} ("
+                "id uuid PRIMARY KEY DEFAULT gen_random_uuid(), "
+                "user_id uuid NOT NULL, body text)"
+            )
+        )
+        for stmt in rls_ddl(TABLE):
+            await s.execute(text(stmt))
+
+
+async def test_rls_enforces_per_user_isolation() -> None:
+    user_a, user_b = uuid.uuid4(), uuid.uuid4()
+    await _create_demo_table()
+    try:
+        # Seed one row per user as the privileged role (superuser bypasses RLS).
+        async with session_scope() as s:
+            await s.execute(
+                text(f"INSERT INTO {TABLE}(user_id, body) VALUES (:u, 'a-note')"),
+                {"u": str(user_a)},
+            )
+            b_id = (
+                await s.execute(
+                    text(f"INSERT INTO {TABLE}(user_id, body) VALUES (:u, 'b-note') RETURNING id"),
+                    {"u": str(user_b)},
+                )
+            ).scalar_one()
+
+        # Scoped to user A: the query has NO user filter, yet only A's row is visible.
+        async with plugin_session(user_a) as s:
+            assert (await s.execute(text("SELECT current_user"))).scalar_one() == "webmail_plugin"
+            visible = (await s.execute(text(f"SELECT user_id FROM {TABLE}"))).scalars().all()
+            assert set(visible) == {user_a}
+            # IDOR blocked: fetching B's row by its exact id returns nothing.
+            got = (
+                await s.execute(text(f"SELECT id FROM {TABLE} WHERE id = :i"), {"i": str(b_id)})
+            ).first()
+            assert got is None
+
+        # WITH CHECK: A cannot insert a row owned by B (error aborts the txn).
+        with pytest.raises(Exception, match="row-level security"):
+            async with plugin_session(user_a) as s:
+                await s.execute(
+                    text(f"INSERT INTO {TABLE}(user_id, body) VALUES (:u, 'forged')"),
+                    {"u": str(user_b)},
+                )
+
+        # A can write its own rows via the SDK session; B's data stays invisible.
+        async with sdk("demo").session(user_a) as s:
+            await s.execute(
+                text(f"INSERT INTO {TABLE}(user_id, body) VALUES (:u, 'a-note-2')"),
+                {"u": str(user_a)},
+            )
+        async with plugin_session(user_a) as s:
+            count = (await s.execute(text(f"SELECT count(*) FROM {TABLE}"))).scalar_one()
+            assert count == 2  # both of A's rows, none of B's
+    finally:
+        async with session_scope() as s:
+            await s.execute(text(f"DROP TABLE IF EXISTS {TABLE}"))
diff --git a/backend/tests/plugins/test_sdk.py b/backend/tests/plugins/test_sdk.py
new file mode 100644
index 0000000..3d1dcd2
--- /dev/null
+++ b/backend/tests/plugins/test_sdk.py
@@ -0,0 +1,51 @@
+"""Plugin SDK facade behaviour (SPEC §11)."""
+
+from __future__ import annotations
+
+import uuid
+
+import pytest
+
+from app.events import get_event_bus
+from app.plugins.sdk import sdk
+
+
+async def test_publish_namespaces_under_plugin_name() -> None:
+    received: list[dict[str, object]] = []
+
+    async def handler(payload: dict[str, object]) -> None:
+        received.append(payload)
+
+    event = f"plugin.demo.thing_{uuid.uuid4().hex[:6]}"
+    suffix = event.removeprefix("plugin.demo.")
+    get_event_bus().subscribe(event, handler)
+
+    await sdk("demo").publish(suffix, {"user_id": "u1", "x": 1})
+    assert received == [{"user_id": "u1", "x": 1}]
+
+
+async def test_publish_requires_user_id() -> None:
+    with pytest.raises(ValueError, match="user_id"):
+        await sdk("demo").publish("thing", {"x": 1})
+
+
+async def test_http_get_uses_ssrf_guard(monkeypatch: pytest.MonkeyPatch) -> None:
+    calls: list[str] = []
+
+    async def fake_guarded_get(url: str) -> str | None:
+        calls.append(url)
+        return f"body:{url}"
+
+    monkeypatch.setattr("app.plugins.sdk.guarded_get", fake_guarded_get)
+    out = await sdk("demo").http_get("http://example.test/x")
+    assert out == "body:http://example.test/x"
+    assert calls == ["http://example.test/x"]
+
+
+def test_sdk_exposes_shared_services() -> None:
+    s = sdk("demo")
+    assert s.name == "demo"
+    assert s.settings is not None
+    # blob store + outbox helpers are reachable through the SDK namespace.
+    assert hasattr(s.blob, "store") and hasattr(s.blob, "load")
+    assert hasattr(s.outbox, "upsert_draft")
diff --git a/backend/tests/plugins/test_types.py b/backend/tests/plugins/test_types.py
new file mode 100644
index 0000000..4b495b5
--- /dev/null
+++ b/backend/tests/plugins/test_types.py
@@ -0,0 +1,34 @@
+"""Frozen plugin contract validation (SPEC §11)."""
+
+from __future__ import annotations
+
+import pytest
+
+from app.plugins.sdk import Plugin, Slot, UiManifest
+
+
+def test_slot_rejects_unknown_name() -> None:
+    Slot(name="message.actions", bundle="/b.js")  # a known slot is fine
+    with pytest.raises(ValueError, match="unknown slot"):
+        Slot(name="mail.everywhere", bundle="/b.js")
+
+
+def test_plugin_name_must_be_identifier_like() -> None:
+    Plugin(name="filters", version="1.0")
+    Plugin(name="my_plugin2", version="1.0")
+    for bad in ("Filters", "2cool", "has-dash", "with space", ""):
+        with pytest.raises(ValueError, match="invalid plugin name"):
+            Plugin(name=bad, version="1.0")
+
+
+def test_plugin_defaults_are_independent() -> None:
+    a = Plugin(name="a", version="1.0")
+    b = Plugin(name="b", version="1.0")
+    assert a.hooks == {} and a.jobs == [] and a.ui_manifest is None
+    a.hooks["x"] = lambda _p: None  # type: ignore[assignment,return-value]
+    assert b.hooks == {}  # default_factory gives each instance its own dict
+
+
+def test_ui_manifest_defaults() -> None:
+    m = UiManifest()
+    assert m.slots == [] and m.pages == [] and m.capabilities == {}
diff --git a/backend/tests/plugins/test_ui_manifest_api.py b/backend/tests/plugins/test_ui_manifest_api.py
new file mode 100644
index 0000000..42c6599
--- /dev/null
+++ b/backend/tests/plugins/test_ui_manifest_api.py
@@ -0,0 +1,73 @@
+"""GET /api/plugins/ui-manifest returns the aggregated manifest (SPEC §11.3)."""
+
+from __future__ import annotations
+
+import uuid
+
+import httpx
+from httpx import ASGITransport
+from sqlalchemy import delete
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import get_settings
+from app.identity.passwords import hash_password
+from app.identity.sessions import create_session
+from app.main import create_app
+from app.models import User
+from app.plugins import loader
+from app.plugins.sdk import Plugin, Slot, UiManifest
+
+
+async def test_ui_manifest_endpoint() -> None:
+    engine = create_async_engine(get_settings().database_url, poolclass=NullPool)
+    sm = async_sessionmaker(engine, expire_on_commit=False)
+    session = sm()
+    user = User(handle=f"ui{uuid.uuid4().hex[:8]}@test.local", password_hash=hash_password("pw"))
+    session.add(user)
+    await session.commit()
+
+    loader.set_plugins_for_test(
+        [
+            Plugin(
+                name="labels",
+                version="1.0",
+                ui_manifest=UiManifest(slots=[Slot(name="message.actions", bundle="/labels.js")]),
+            )
+        ]
+    )
+
+    token = await create_session(user.id, "pytest")
+    transport = ASGITransport(app=create_app())
+    client = httpx.AsyncClient(
+        transport=transport, base_url="http://testserver", cookies={"session": token}
+    )
+    try:
+        # Unauthenticated request is rejected.
+        async with httpx.AsyncClient(
+            transport=transport, base_url="http://testserver"
+        ) as anon:
+            assert (await anon.get("/api/plugins/ui-manifest")).status_code == 401
+
+        resp = await client.get("/api/plugins/ui-manifest")
+        assert resp.status_code == 200
+        body = resp.json()
+        assert body == {
+            "plugins": [
+                {
+                    "name": "labels",
+                    "version": "1.0",
+                    "builtin": False,
+                    "slots": [{"name": "message.actions", "bundle": "/labels.js"}],
+                    "pages": [],
+                    "capabilities": {},
+                }
+            ]
+        }
+    finally:
+        await client.aclose()
+        async with sm() as cleanup:
+            await cleanup.execute(delete(User).where(User.id == user.id))
+            await cleanup.commit()
+        await session.close()
+        await engine.dispose()
diff --git a/backend/workers/run.py b/backend/workers/run.py
index 9d4a4d5..7c84cfd 100644
--- a/backend/workers/run.py
+++ b/backend/workers/run.py
@@ -33,7 +33,13 @@ logger = logging.getLogger(__name__)
 _SHUTDOWN_DRAIN_S = 10.0  # §7: release leases + drain within this budget
 
 
-def _worker(functions: list[Any], queue_name: str, max_jobs: int, job_timeout: int) -> Worker:
+def _worker(
+    functions: list[Any],
+    queue_name: str,
+    max_jobs: int,
+    job_timeout: int,
+    cron_jobs: list[Any] | None = None,
+) -> Worker:
     return Worker(
         functions=functions,
         queue_name=queue_name,
@@ -41,6 +47,7 @@ def _worker(functions: list[Any], queue_name: str, max_jobs: int, job_timeout: i
         max_jobs=max_jobs,
         job_timeout=job_timeout,
         handle_signals=False,  # the runner owns signal handling (graceful shutdown)
+        cron_jobs=cron_jobs or [],
     )
 
 
@@ -49,8 +56,19 @@ def build_arq_workers(role: str) -> list[Worker]:
     s = get_settings()
     if role not in ("jobs", "all"):
         return []
+    # Plugin jobs (SPEC §11.2) join the interactive queue; cron-scheduled ones run
+    # on that worker too. With no plugins installed these are empty (inert).
+    from app.plugins.jobs import plugin_arq_functions, plugin_cron_jobs
+
+    interactive: list[Any] = [*INTERACTIVE_FUNCTIONS, *plugin_arq_functions()]
     return [
-        _worker(INTERACTIVE_FUNCTIONS, QUEUE_INTERACTIVE, s.interactive_concurrency, 120),
+        _worker(
+            interactive,
+            QUEUE_INTERACTIVE,
+            s.interactive_concurrency,
+            120,
+            cron_jobs=plugin_cron_jobs(),
+        ),
         _worker(BULK_FUNCTIONS, QUEUE_BULK, s.bulk_concurrency, 3600),
     ]
 
@@ -59,6 +77,13 @@ async def _run() -> None:
     logging.basicConfig(level=get_settings().log_level)
     role = get_settings().worker_role
 
+    # Subscribe plugin hooks so events published during sync (message.new, …) reach
+    # them in this process too (SPEC §11; the API process registers separately).
+    from app.events import get_event_bus
+    from app.plugins import loader
+
+    loader.register_hooks(get_event_bus())
+
     coordinator = SyncCoordinator() if role in ("sync", "all") else None
     if coordinator is not None:
         await coordinator.start()