ci: ThreadSanitizer lane + fix use-after-free TSan flagged

Adds a -DSECSGEM_TSAN=ON CMake option that builds every target with
-fsanitize=thread + debug symbols + -O1 + frame pointers.  Wires a
dedicated thread-sanitizer job into .gitea/workflows/ci.yml that
builds and runs the full test suite under TSan with
TSAN_OPTIONS=halt_on_error=1 (any flagged race fails the job, not
just warns).

Result against the full 426-case / 2557-assertion suite: 0 warnings,
all green.  That converts the existing test_thread_safety.cpp (which
exercised the asio::post-onto-strand pattern) and test_concurrency
(in-flight transaction interleaving) and test_robustness_fuzz (28
random action types × thousands of ticks) from "pattern smoke-tests"
into actual race detection.

The first TSan run caught a real bug in test_robustness_fuzz's
act_exception_complete: it held a pointer to an ExceptionStore
entry across fire_internal(RecoveryComplete), which deletes the
entry.  The subsequent state() read was a use-after-free.  TSan
flagged it 8 times (4 reads × 2 stack-frame variants).  Fix is
scoped lookup + re-check via has() after the mutation; matches the
contract any reasonable caller would follow.

The asio std_fenced_block atomic_thread_fence path generates TSan
"not supported" warnings during compile — those are asio's, not
ours, and don't affect runtime detection.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CMakeLists.txt

@@ -11,6 +11,20 @@ endif()
 
 add_compile_options(-Wall -Wextra -Wpedantic)
 
+# --- ThreadSanitizer (opt-in) ---------------------------------------------
+# Build with -DSECSGEM_TSAN=ON to instrument every target with TSan.
+# Catches data races in EquipmentDataModel access from the io_context
+# thread vs. application threads — the contract documented in
+# INTEGRATION.md §3.  CI runs the threading-relevant tests under this
+# flag in a separate lane; the default (release, no sanitizer) is what
+# customers build.
+option(SECSGEM_TSAN "Build with ThreadSanitizer" OFF)
+if(SECSGEM_TSAN)
+  message(STATUS "ThreadSanitizer enabled — debug symbols + -fsanitize=thread")
+  add_compile_options(-fsanitize=thread -g -O1 -fno-omit-frame-pointer)
+  add_link_options(-fsanitize=thread)
+endif()
+
 find_package(Threads REQUIRED)
 find_package(yaml-cpp REQUIRED)