Marks a Secret node whose value is interpolated into a CLI flag argument (e.g. -var "key=$(SECRET)").
CLI flag values appear in pipeline log output even when ADO secret masking is active,
because the command string is logged before masking runs and Terraform itself logs -var values.
Marks an Identity node as implicitly injected by the platform (e.g. ADO System.AccessToken).
Implicit tokens are structurally accessible to all tasks by platform design — exposure
to untrusted steps is Info-level (structural) rather than Critical (misconfiguration).
Returns true if ref_str is a SHA-pinned action reference.
Checks: contains @, part after @ is >= 40 hex chars.
Single source of truth — used by both parser and rules.