svcforge: reference implementation

Complete working build of the system learn-python/ teaches.
164 tests, mypy --strict clean, domain coverage 99%.

tests/integration/test_claim.py

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+"""The claim race. If only one test in this repo survives, it should be this one."""
+
+from __future__ import annotations
+
+import asyncio
+
+from svcforge_core.domain.models import TaskKind
+from svcforge_core.repo.db import DictPool
+from svcforge_core.repo.tasks import TaskRepo
+from tests.integration.helpers import make_instance
+
+
+async def test_skip_locked_claims_each_task_exactly_once(pool: DictPool) -> None:
+    """50 workers, 50 tasks, one claim each — no double-claims, no lost tasks.
+
+    This is the test that fails if you split the claim into select-then-update.
+    """
+    repo = TaskRepo(pool)
+    inst = await make_instance(pool)
+    ids = {await repo.enqueue_standalone(inst, TaskKind.PROVISION) for _ in range(50)}
+
+    async with asyncio.TaskGroup() as tg:
+        claims = [tg.create_task(repo.claim(f"w{i}")) for i in range(50)]
+    got = [c.result() for c in claims]
+
+    assert all(t is not None for t in got)
+    assert sorted(t.id for t in got if t is not None) == sorted(ids)  # each exactly once
+    assert all(t.attempts == 1 for t in got if t is not None)
+
+
+async def test_more_workers_than_tasks_get_none_not_a_duplicate(pool: DictPool) -> None:
+    """Contention must produce None for the losers, never a second claim on one row."""
+    repo = TaskRepo(pool)
+    inst = await make_instance(pool)
+    await repo.enqueue_standalone(inst, TaskKind.PROVISION)
+
+    async with asyncio.TaskGroup() as tg:
+        claims = [tg.create_task(repo.claim(f"w{i}")) for i in range(10)]
+    got = [c.result() for c in claims]
+
+    won = [t for t in got if t is not None]
+    assert len(won) == 1
+    assert len([t for t in got if t is None]) == 9