Lock stacks during compose runs, cache stats, persist runtime state (0.47.0)

F7 — Nothing stopped two compose operations landing on the same stack. There
was a busy flag, but is_busy() was only ever read to colour the status column;
no lifecycle handler consulted it before acting. Two tabs, or auto-update
picking up a stack somebody had just clicked, both ran pull + up -d against the
same project and raced over recreating containers.

Lifecycle calls, the two deploy WebSockets and the auto-update pass now take a
real lock; a second caller gets 409 (or an error frame and close 4409) and
auto-update skips and retries next cycle. The lock is a row rather than a set
in one worker's memory, so it holds across workers and across a restart, and it
carries an expiry — a worker killed mid-deploy would otherwise strand the stack
with no fix short of editing the database.

F10 — /api/stacks/stats sampled every running container on every call, one
blocking daemon request each, and both the dashboard and the stacks list poll
it every five seconds. Two tabs on a 40-container host meant a sustained ~16
samples a second. Cached for 4s behind a lock so concurrent callers share one
sweep, the same shape dashboard_service already used for its fleet aggregate.

F11 — Three module dicts assumed exactly one uvicorn worker without saying so
and were lost on restart. The busy set is the lock above. The image update
cache is now mirrored to SQLite, so a restart shows the badges immediately
instead of blanking them for up to an hour, and the already-notified marks come
back with them rather than re-announcing the same updates. The login rate
limiter is a table, so it cannot be cleared by getting the process to restart
and no longer multiplies by the worker count.

The constraint that shaped this: compose_service and update_service are shared
with the agent, which has no database. Neither may import one. So the lock is a
separate service the central app enforces at its own entry points, and update
persistence is an opt-in callback the central app registers in its lifespan —
the agent registers nothing and behaves exactly as before. A test asserts
update_service never imports the database, since that is the kind of thing a
later change breaks silently.

Both new nets were checked by reverting the fix: dropping the lock from
_lifecycle fails six tests, removing the stats cache fails the one that names
the behaviour.

Also wires up cache pruning in the same sweep — without it both the dict and
the table grew one entry per image tag ever run, for the life of the install.

31 new tests (729 total).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Dk43rmEeRfYi5wsLDbmfyG

backend/services/auto_update_service.py

@@ -20,7 +20,13 @@ from database import engine
 from models.agent import Agent
 from models.auto_update import AutoUpdate
 from models.setting import EVENT_PULL_FAILED, EVENT_STACK_AUTO_UPDATED
-from services import agent_service, compose_service, notify_service, update_service
+from services import (
+    agent_service,
+    compose_service,
+    notify_service,
+    stack_lock_service,
+    update_service,
+)
 
 logger = logging.getLogger("stackpilot.autoupdate")
 
@@ -104,8 +110,15 @@ async def _run_local(session: Session, policy: AutoUpdate) -> None:
     prev = policy.last_status
     if policy.redeploy:
         try:
-            await compose_service.pull(stack_id)
-            await compose_service.up(stack_id)
+            # Never redeploy underneath somebody: if a user is mid-deploy on
+            # this stack, skip and pick it up next cycle rather than racing
+            # them over the same containers.
+            with stack_lock_service.hold(session, stack_id, "auto-update", "auto-update"):
+                await compose_service.pull(stack_id)
+                await compose_service.up(stack_id)
+        except stack_lock_service.StackBusy as exc:
+            _record(session, policy, "skipped", str(exc))
+            return
         except Exception as exc:  # noqa: BLE001
             _record(session, policy, "error", str(exc))
             await _safe_notify(EVENT_PULL_FAILED, f"Auto-update of '{stack_id}' failed", str(exc), session)