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SECURITY.md

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+# Security policy
+
+`schedls` writes scheduler configuration and, when run as root, writes files in
+privileged locations. Security is therefore a primary design concern.
+
+## Reporting a vulnerability
+
+Report suspected vulnerabilities privately to the maintainer listed in
+`pyproject.toml`. Do not open a public issue for a security-sensitive report.
+
+## Promises
+
+`schedls` does not:
+
+- run a background daemon;
+- listen on a network port;
+- make network requests;
+- automatically invoke `sudo`, `su`, `pkexec`, or any other privilege
+  escalation mechanism;
+- execute discovered scheduled commands;
+- open an editor or pager while managing jobs;
+- use a shell internally for helper commands (`shell=True` is forbidden);
+- modify unmanaged schedules by default.
+
+## Security model
+
+See [docs/security-model.md](docs/security-model.md) for the threat model and
+the mitigations implemented in this repository.
+
+## Release checklist
+
+Before every release:
+
+```text
+[ ] No new shell=True usage
+[ ] No automatic privilege escalation
+[ ] No new implicit command execution
+[ ] No pager/editor invocation under privilege
+[ ] Unit serialization tests pass
+[ ] Cron serialization tests pass
+[ ] Symlink tests pass
+[ ] Atomic-write tests pass
+[ ] Trusted-directory ownership/mode tests pass
+[ ] Helper resolution ownership tests pass
+[ ] Unit-name path traversal tests pass
+[ ] Log sanitization tests pass
+[ ] Dependency audit passes
+[ ] JSON schema changes reviewed
+[ ] New mutating operations support --dry-run
+[ ] New mutating operations have clear confirmation behavior
+[ ] Documentation describes new filesystem/state changes
+```