feat(audit): fit the audit tools into the agent surface (P8)

After P5 merged first: a close leads to the audit and the period's
attestation, an audit run to its workpaper and the claims behind it, the
attest tools to the attestations and the CPA package; a refusal for want of
a standing audit is the guard audit_required with books.audit as its
remedy; the audit prompt runs the audit tools. policy.cpa_package_requires_audit,
unset, refuses once the books hold an audit run and warns before, so a
book that has not begun the programme is not stopped from its first handoff
by a rule it has not met; set to refuse, it holds from the start.
bookspec states B-45 (convention) in its checker.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

checker/src/rules.rs

@@ -123,7 +123,7 @@ pub struct Rule {
     /// Its normative title, as `docs/spec/rules.md` states it.
     pub title: &'static str,
     /// What its statement rests on; `None` for a rule allocated but not
-    /// yet stated (B-39 to B-45, `plan/served.md` 8.0.3).
+    /// yet stated (B-39, B-40 and B-43, `plan/served.md` 8.0.3).
     pub status: Option<Status>,
     /// The example ids that demonstrate it, by `Example::id`.
     pub examples: &'static [&'static str],
@@ -587,8 +587,8 @@ const SPEC: Spec = &[
     (
         45,
         Area::Ledger,
-        "Audits and attestations (allocated, not yet stated)",
+        "An audit is deterministic over the books; an attestation is a claim by a named client",
-        None,
+        Some(Status::Convention),
         &[],
     ),
 ];