test: unit suite for the gateway invariants plus an integration slice

Covers routing, failover, the circuit breaker, structured-output retries, the
cache-prefix validator, cost computation including cached-token pricing, the
daily budget breaker, the quota protocol, the task state machine and log
redaction. HTTP is mocked -- no unit test spends money. The integration test
runs the real slice against PostgreSQL and Redis with a faked provider.

tests/unit/test_ids.py

@@ -0,0 +1,55 @@
+"""Snowflake ids (架构文档 §6.1 原则 2)."""
+
+from __future__ import annotations
+
+import pytest
+
+from packages.domain.ids import (
+    DEFAULT_EPOCH_MS,
+    SnowflakeGenerator,
+    next_id,
+    timestamp_ms_of,
+)
+
+
+def test_ids_are_unique_and_monotonic() -> None:
+    generator = SnowflakeGenerator(node_id=1)
+    ids = [generator.next_id() for _ in range(5000)]
+    assert len(set(ids)) == len(ids)
+    assert ids == sorted(ids)
+
+
+def test_ids_fit_in_a_signed_64_bit_integer() -> None:
+    assert 0 < next_id() < 2**63
+
+
+def test_different_nodes_do_not_collide() -> None:
+    a = SnowflakeGenerator(node_id=1)
+    b = SnowflakeGenerator(node_id=2)
+    assert not {a.next_id() for _ in range(500)} & {b.next_id() for _ in range(500)}
+
+
+def test_node_id_is_bounded() -> None:
+    with pytest.raises(ValueError, match="node_id"):
+        SnowflakeGenerator(node_id=1024)
+
+
+def test_timestamp_is_recoverable_for_partition_pruning() -> None:
+    generator = SnowflakeGenerator(node_id=3)
+    recovered = timestamp_ms_of(generator.next_id())
+    assert recovered > DEFAULT_EPOCH_MS
+
+
+def test_sequence_rollover_within_one_millisecond() -> None:
+    """More than 4096 ids in a single ms must wait, not duplicate."""
+    frozen = DEFAULT_EPOCH_MS + 1_000
+    calls = {"n": 0}
+
+    def fake_now() -> int:
+        calls["n"] += 1
+        # Hold the clock for the first 5000 calls, then let it advance.
+        return frozen if calls["n"] < 5000 else frozen + 1
+
+    generator = SnowflakeGenerator(node_id=1, clock=fake_now)
+    ids = [generator.next_id() for _ in range(4200)]
+    assert len(set(ids)) == len(ids)