The embedded Hindsight daemon's profile env file carries the plaintext
HINDSIGHT_API_LLM_API_KEY but was written via bare write_text(), leaving
it with umask-derived (typically world-readable) permissions.
- Create/truncate the file via os.open(..., 0o600); chmod a pre-existing
file to 0600 BEFORE writing new secret bytes.
- Post-write validation on POSIX: verify 0600, retry chmod, and raise if
the file still isn't owner-only.
- If validation fails, unlink the secret file so a plaintext key is never
left behind with unverified permissions.
- Regression tests under tests/plugins/ for fresh-write mode, tightening a
pre-existing 0644 file, and cleanup on validation failure.
Narrowed reimplementation of #74236 confined to plugins/memory/hindsight/;
the core utils.py atomic-replace opt-out from the PR was dropped.
Co-authored-by: carrion256 <carrion256@proton.me>
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