oasdiff does not enforce --allow-external-refs=false on the git-revision load path (SSRF / local file read)

From v1.13.2 through v1.18.0, oasdiff did not enforce --allow-external-refs=false (library: openapi3.Loader.IsExternalRefsAllowed = false) when loading a spec from a git revision (the rev:path form, e.g. main:openapi.yaml). External $refs were resolved on that load path even when external refs were explicitly disabled, so the mitigation silently did not apply there.

A caller who set --allow-external-refs=false specifically to safely process untrusted specs remained exposed — on the git-revision load path only — to:

• SSRF via $ref: "http://<internal-host>/…", and
• Local file reads via $ref: "/path" or file://.

Affected callers:

• CLI: oasdiff diff main:openapi.yaml HEAD:openapi.yaml --allow-external-refs=false (and breaking / changelog / summary, and the git-diff-driver) run over untrusted spec content.
• Go library consumers of github.com/oasdiff/oasdiff/load that set IsExternalRefsAllowed = false and load from a git-revision source via load.NewSpecInfo.

The file and URL load paths correctly enforced the setting; only the git-revision path was affected. Callers that left external refs at the default (true) are not in scope for this advisory.

v1.18.1 enforces the external-refs policy on the git-revision path (so --allow-external-refs=false now blocks external $refs there) and returns a dedicated exit code (123) when an external $ref is refused.

• Upgrade to v1.18.1, or
• Avoid the git-revision input form when processing untrusted specs with external refs disabled.

• Introduced in v1.13.2 (#832, which added $ref-chain resolution on the git-revision path); fixed in v1.18.1 (#974, #975).
• The permissive default (allow-external-refs: true) and its zero-interaction exposure in CI via the GitHub Action is tracked separately in GHSA-fhj3-7267-7vv5 (oasdiff-action).