safe_load() raises ComposerError on multi-document streams (k8s manifests)
and ConstructorError on application-defined tags (CloudFormation !Sub,
Ansible !vault) — both valid YAML syntax. Now that the linter's verdict is
a fail-closed write gate, those false positives would refuse legitimate
writes outright. Switch to yaml.parse() (scanner+parser only), which still
catches real syntax failures.
write_file() previously called _atomic_write() first and only ran the
JSON/YAML/TOML/Python syntax check afterward as an informational lint
delta -- a parse failure never set the top-level `error` key, so a
corrupt structured-data write still landed on disk (and file_tools.py's
files_modified gating, which keys off `error`, silently reported it as
a successful modification).
Move the in-process syntax check for JSON/YAML/TOML ahead of
_atomic_write() and refuse the write outright on a parse failure: no
temp file, no rename, nothing touches disk, and the result carries a
top-level `error` so callers correctly see it as unmodified.
Deliberately scoped to _FAIL_CLOSED_INPROC_EXTS (JSON/YAML/TOML), not
all of LINTERS_INPROC -- .py is excluded because this codebase's own
test fixtures (TestPatchReplacePostWriteVerification et al.) write
arbitrary non-Python text through *.py paths purely to exercise
write-mechanics; a hard block there broke 3 previously-passing tests
during development. Python keeps its pre-existing non-blocking
lint-delta report.
Adds tests/tools/test_write_file_syntax_gate.py: invalid JSON/YAML/YML/
TOML refused with nothing written (new file) and nothing modified
(existing file); valid JSON/YAML still written byte-for-byte; a
non-linted extension with garbage content is unaffected; invalid Python
is confirmed NOT hard-refused (still just reported).
