Enforce the Devii task quotas with atomic reservations

The creation and run quotas were checked and then acted on, so two concurrent
create_task calls or two schedulers could both pass the check and overshoot the
limit. Both are now a single conditional INSERT decided on the driver rowcount:
reserve_run takes a run slot after the claim and releases the claim by deferring
when the quota is spent, and insert_task_within_quota does the same for the task
row itself. Racing twelve and sixteen processes now yields exactly the limit.

The atomic insert names its columns, and dataset skips a None valued key when it
creates a table lazily, so the store declares the full task column set up front.
Both the column and index ensures now tolerate a concurrent duplicate, since
several processes build a store at once and SQLite DDL is not idempotent.

Adds the quota, task-run context, guard, store and scheduler test suites, and
documents the chokepoints and the unhackable task-run flag.

tests/unit/services/devii/tasks/guards.py

@@ -24,6 +24,8 @@ from devplacepy.services.devii.tasks.limits import reserve_run
 from devplacepy.services.devii.tasks.schedule import now_utc, to_iso
 from devplacepy.utils import generate_uid
 
+SIGNUP_AFTER_PRIMARY_ADMIN = "2099-01-01T00:00:00"
+
 
 def _account(local_db, role):
     uid = generate_uid()
@@ -33,7 +35,7 @@ def _account(local_db, role):
             "username": f"guard-{uid[-10:]}",
             "role": role,
             "deleted_at": None,
-            "created_at": to_iso(now_utc()),
+            "created_at": SIGNUP_AFTER_PRIMARY_ADMIN,
         }
     )
     invalidate_admins_cache()
@@ -55,11 +57,7 @@ def _row(owner_uid, **overrides):
 def _burn_runs(local_db, owner, count, reference):
     for index in range(count):
         limits.record_run(
-            local_db,
-            "user",
-            owner,
-            generate_uid(),
-            reference - timedelta(minutes=index),
+            local_db, "user", owner, generate_uid(), reference - timedelta(minutes=index)
         )
 
 
@@ -94,6 +92,13 @@ def test_exhausted_task_is_retired(local_db):
     assert retire_reason(_row(owner, max_runs=5, run_count=5), now_utc()) == REASON_MAX_RUNS
 
 
+def test_task_without_an_expiry_stops_at_the_fallback_ceiling(local_db):
+    owner = _account(local_db, "Member")
+    now = now_utc()
+    row = _row(owner, created_at=to_iso(now - timedelta(days=40)))
+    assert retire_reason(row, now) == REASON_EXPIRED
+
+
 def test_repeated_failures_retire_the_task(local_db):
     owner = _account(local_db, "Member")
     row = _row(owner, failure_count=3)
@@ -133,13 +138,11 @@ def test_administrator_run_quota_is_larger(local_db):
 def test_budget_defers_the_task(local_db):
     owner = _account(local_db, "Member")
     now = now_utc()
-    postponement = budget_deferral(
-        _row(owner), now, budget_exceeded=lambda kind, uid: True
-    )
+    postponement = budget_deferral(_row(owner), now, budget_exceeded=lambda k, u: True)
     assert postponement is not None
     assert postponement.reason == REASON_BUDGET
     assert postponement.retry_at > now
-    assert budget_deferral(_row(owner), now, lambda kind, uid: False) is None
+    assert budget_deferral(_row(owner), now, lambda k, u: False) is None
     assert budget_deferral(_row(owner), now, None) is None