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.

devplacepy/services/devii/tasks/limits.py

@@ -85,12 +85,12 @@ def window_start(reference: datetime) -> datetime:
     return reference - timedelta(hours=WINDOW_HOURS)
 
 
-def _stamps(db: Any, sql: str, table: str, owner_kind: str, owner_id: str, cutoff: str) -> list[str]:
+def _stamps(
+    db: Any, sql: str, table: str, owner_kind: str, owner_id: str, cutoff: str
+) -> list[str]:
     if table not in db.tables:
         return []
-    rows = db.query(
-        sql, kind=owner_kind, owner=owner_id, cutoff=cutoff, cap=SAMPLE_CAP
-    )
+    rows = db.query(sql, kind=owner_kind, owner=owner_id, cutoff=cutoff, cap=SAMPLE_CAP)
     return [str(row["created_at"]) for row in rows if row.get("created_at")]
 
 
@@ -127,7 +127,9 @@ def create_quota(db: Any, owner_kind: str, owner_id: str, reference: datetime) -
     return _quota(stamps, limit)
 
 
-def record_run(db: Any, owner_kind: str, owner_id: str, task_uid: str, reference: datetime) -> None:
+def record_run(
+    db: Any, owner_kind: str, owner_id: str, task_uid: str, reference: datetime
+) -> None:
     from devplacepy.utils import generate_uid
 
     db[RUNS_TABLE].insert(
@@ -149,10 +151,7 @@ def reserve_run(
     from devplacepy.utils import generate_uid
 
     limit = run_limit(owner_is_admin(owner_id))
-    if RUNS_TABLE not in db.tables:
-        record_run(db, owner_kind, owner_id, task_uid, reference)
-        return True
-    if limit <= 0:
+    if limit <= 0 or RUNS_TABLE not in db.tables:
         record_run(db, owner_kind, owner_id, task_uid, reference)
         return True
     params = {

devplacepy/services/devii/tasks/scheduler.py

@@ -8,7 +8,7 @@ from typing import Any, Awaitable, Callable, Optional
 
 from .context import task_run_scope
 from .controller import compute_followup
-from .guards import BudgetProbe, Deferral, budget_deferral, run_deferral, retire_reason
+from .guards import BudgetProbe, Deferral, budget_deferral, retire_reason, run_deferral
 from .limits import reserve_run
 from .schedule import next_run, now_utc, to_iso
 from .store import TaskStore, claim, due_rows
@@ -102,10 +102,7 @@ def defer(store: TaskStore, row: dict[str, Any], postponement: Deferral) -> None
         },
     )
     logger.info(
-        "Task uid=%s postponed to %s: %s",
-        row.get("uid"),
-        retry_at,
-        postponement.reason,
+        "Task uid=%s postponed to %s: %s", row.get("uid"), retry_at, postponement.reason
     )
     _audit_task_deferred(row, postponement.reason, retry_at)
 

devplacepy/services/devii/tasks/store.py

@@ -148,9 +148,7 @@ class TaskStore:
     def require_creation_allowed(self) -> None:
         if self._operator:
             return
-        denial = creation_denial(
-            self._db, self._owner_kind, self._owner_id, now_utc()
-        )
+        denial = creation_denial(self._db, self._owner_kind, self._owner_id, now_utc())
         if denial is not None:
             raise denial