Add a root-overridable self-test harness for scripts/check-source-safety.sh so the guard can be tested against synthetic trees without scanning the real repository.
Cover clean input, MCP/server stdout writes, unsafe string APIs, and new raw filesystem APIs in production diffs. Add a dedicated lint-source-safety target because the broader lint-no-suppress path is currently blocked by existing NOLINT audit failures before this guard can run.
Validation: bash scripts/test-source-safety.sh; bash scripts/check-source-safety.sh; git diff --check; make -f Makefile.cbm lint-source-safety.
Signed-off-by: Andrew Hundt <ATHundt@gmail.com>