[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>

pyproject.toml

@@ -69,6 +69,10 @@ include = ["gps_denied_onboard*"]
 minversion = "7.0"
 testpaths = ["tests"]
 pythonpath = ["src"]
+# log_schema.py is the contract-mandated file name (AZ-245 AC-4); kept
+# in python_files so the contract test is discovered alongside the
+# standard `test_*.py` pattern.
+python_files = ["test_*.py", "*_test.py", "log_schema.py"]
 addopts = [
     "--strict-markers",
     "-ra",
@@ -79,6 +83,7 @@ markers = [
     "docker: tests that require Docker compose services",
     "ardupilot_sitl: tests that require ArduPilot SITL container",
     "slow: tests slower than ~5s",
+    "contract: contract-suite test (frozen public surfaces)",
 ]
 
 [tool.coverage.run]