fix: add TSan suppressions file and use absolute path in CI

The TSan CI job referenced tsan_suppressions.txt with a relative path,
which resolved against the test binary directory instead of the repo root.

- Create tsan_suppressions.txt with Rust FFI suppressions
- Use $GITHUB_WORKSPACE absolute path in TSAN_OPTIONS

Author: siddimore

.github/workflows/builds.yml

@@ -343,7 +343,7 @@ jobs:
           - name: tsan
             preset: linux-debug-tsan
             build_dir: build-debug-tsan
-            env_vars: "TSAN_OPTIONS=suppressions=tsan_suppressions.txt:halt_on_error=1"
+            env_vars: "TSAN_OPTIONS=suppressions=$GITHUB_WORKSPACE/tsan_suppressions.txt:halt_on_error=1"
 
     name: Sanitizer (${{ matrix.name }})
     runs-on: ubuntu-latest

tsan_suppressions.txt

@@ -0,0 +1,16 @@
+# ThreadSanitizer suppressions for livekit client-sdk-cpp
+#
+# Rust FFI layer may trigger false positives in TSan because
+# TSan cannot see synchronization inside the Rust runtime.
+# Add specific suppressions here as needed.
+#
+# Syntax:
+#   race:<function_or_source_pattern>
+#   deadlock:<function_or_source_pattern>
+#   mutex:<function_or_source_pattern>
+
+# Rust standard library internals
+race:libstd-*.so
+
+# Rust FFI bridge (livekit_ffi)
+race:livekit_ffi_*