[AZ-273] [AZ-274] [AZ-275] [AZ-267] [AZ-268] FDR producer chain + log bridge + contract test

AZ-273: lock-free SPSC ring buffer with pre-allocated slots, power-of-
two capacity, opt-in SPSC guard, and EnqueueResult / FdrSpscViolationError
on the public surface. make_fdr_client caches one client per producer_id
and reads capacity from config.fdr.per_producer_capacity with fallback
to queue_size.
AZ-274: default_overrun_policy implements drop-oldest + retry + immediate
marker emission, with prior-marker dropped_count folding via _evict_one
so user-loss info is never lost across iterations. ERROR diagnostic is
rate-limited to <=1/sec per producer.
AZ-275: FakeFdrSink mirrors the FdrClient public surface and reuses the
production default_overrun_policy via a duck-typed _PolicyAdapter. The
test-only records/all_records_ever properties let component tests assert
both in-buffer and lifetime state. tests/conftest.py registers the
fake_fdr_sink fixture and an AST architecture lint forbids production
imports of fakes.
AZ-267: FdrLogBridgeHandler installs on the root logger via wire_log_bridge
and forwards only WARN+ERROR records into the FDR with kind="log".
Thread-local recursion guard short-circuits internal logging; saturated-
queue diagnostics go to stderr every N=1000 drops.
AZ-268: tests/contract/log_schema.py covers every row of the schema's
Test Cases table plus the "DEBUG+INFO never reach FDR" invariant.
pyproject.toml registers the contract pytest marker and the
contract-mandated log_schema.py file-name.
251 unit + contract tests pass (48 new). Review verdict:
PASS_WITH_WARNINGS; findings are NFR-perf deferrals + documented
relaxation of AZ-274 AC-2 coalescing under permanently-stalled consumer.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/conftest.py

@@ -10,9 +10,12 @@ Tier-2-only tests are guarded by `pytest.mark.tier2` and auto-skipped on Tier-1.
 from __future__ import annotations
 
 import os
+from collections.abc import Iterator
 
 import pytest
 
+from gps_denied_onboard.fdr_client.fakes import FakeFdrSink
+
 
 def pytest_collection_modifyitems(config: pytest.Config, items: list[pytest.Item]) -> None:
     """Auto-skip `tier2` tests when GPS_DENIED_TIER != 2."""
@@ -28,3 +31,11 @@ def pytest_collection_modifyitems(config: pytest.Config, items: list[pytest.Item
             item.add_marker(skip_gpu)
         if "docker" in item.keywords:
             item.add_marker(skip_docker)
+
+
+@pytest.fixture
+def fake_fdr_sink() -> Iterator[FakeFdrSink]:
+    """Default-configuration FakeFdrSink with overrun policy disabled (AZ-275 AC-5)."""
+    sink = FakeFdrSink(producer_id="test.producer")
+    yield sink
+    sink.flush()