[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>

src/gps_denied_onboard/fdr_client/__init__.py

@@ -4,7 +4,12 @@ Producer-side API used by every component. Consumer-side writer lives in
 `gps_denied_onboard.components.c13_fdr` (AZ-248 / E-C13).
 """
 
-from gps_denied_onboard.fdr_client.client import FdrClient
+from gps_denied_onboard.fdr_client.client import (
+    EnqueueResult,
+    FdrClient,
+    FdrSpscViolationError,
+    make_fdr_client,
+)
 from gps_denied_onboard.fdr_client.records import (
     CURRENT_SCHEMA_VERSION,
     KNOWN_KINDS,
@@ -23,9 +28,12 @@ __all__ = [
     "MAX_INLINE_BLOB_BYTES",
     "OVERRUN_KIND",
     "OVERRUN_PRODUCER_ID",
+    "EnqueueResult",
     "FdrClient",
     "FdrRecord",
     "FdrSchemaError",
+    "FdrSpscViolationError",
+    "make_fdr_client",
     "parse",
     "serialise",
 ]