Sigil concerns verifiable agent identity and authority — the correctness of these mechanisms is the whole point of the project. We take security seriously and welcome responsible disclosure.

• Do not open a public issue for a security vulnerability.
• Report privately via GitHub's private vulnerability reporting (the repository's Security → Report a vulnerability).
• Please include: a description, the affected component and version/commit, reproduction steps, and the impact.

• An acknowledgement of your report, an assessment, and coordinated disclosure once a fix or mitigation is available.
• Credit for the reporter, if desired.

• In scope: the Sigil specification and reference implementation in this repository.
• Out of scope here: the underlying Archon infrastructure — report those to the Archon project.

Because Sigil is an identity/authority layer, the security-sensitive properties are not only memory-safety bugs but the invariants themselves: holder binding (a credential is never bearer), monotonic attenuation (delegation only narrows), fail-closed revocation, verify-before-interact, and "a published value carries no capability." A break in one of these is a security issue even if no code crashes. Report those too.