feat(bookspec): rule identifiers from B-1 to B-45 (P13)

Every rule of `docs/spec/rules.md` now has one bookspec identifier,
`BS-<area>-<n>`: eleven areas (entry, ledger, statement, period, partner,
asset, prepaid, arap, revenue, 1099, format), numbered in B-rule order
within its area. The table is `bookspec/spec/rules-index.md`, and each
stated rule carries its id under its heading in `docs/spec/rules.md`, so
a reader of either can find the other.

rules.md's DECISION status becomes bookspec's CHOICE: the specification
names the options and an engine declares its pick (`Claims::with_choice`),
which is what an example already meant by `status = "CHOICE"`. B-39 to
B-45 are allocated in `plan/served.md` 8.0.3 and not yet stated: they
carry an id and an area and no status, so a later unit fills them in
without moving anyone else's number.

The catalogue names the examples that demonstrate each rule (56 files,
each under at least one rule) and the rule each refusal reason belongs
to. A rule with no example cannot be claimed: a claim needs evidence.
`docs/architecture.md`, `docs/testing.md` (tests and the For-P12
mutation targets) and `docs/parity.md` record the new shape; the
bookspec README points at the checker, the runner and the adapter.

docs/architecture.md

@@ -134,3 +134,35 @@ tokio mutex never poisons. So the server fails closed: a panic in a
 request (its task, or while it holds the guard) sets `stopped`, and every
 later request, on every session, is refused until a restart, which
 re-verifies the journal.
+
+## bookspec (`bookspec/`, P13)
+
+bookspec is the formal accounting specification (D-34): every rule stated
+normatively, sourced, with a symbolic form and concrete examples, and a
+conformance harness any engine can be run against. It lives in its own
+Cargo workspace inside this repository until the harness is stable enough
+to move to its own repository (P13 step 6, D-34, Z-17):
+
+- `bookspec/checker` is engine-independent: the example schema and its
+  parser (`Example::from_toml`, every structure `deny_unknown_fields`, the
+  cross-field shape checked by `Example::validate`), the rule catalogue
+  (`rules()`, `RuleId` `BS-<area>-<n>`, the refusal-to-rule table) and the
+  `Engine` trait (`load`, `apply`, `query`, `claims`, and `change` for a
+  `[[changes]]` entry, which posts no entry and so is neither a setup nor
+  an event).
+- `bookspec/runner` drives any `Engine` through the examples and reports
+  per rule: pass, fail or not claimed. It compares the engine's answers
+  with the examples' exact expected values; it never asks the engine
+  whether its own answer is right.
+- `bookspec/spec/rules-index.md` maps B-1 to B-45 to the bookspec ids;
+  `docs/spec/rules.md` carries each stated rule's id under its heading.
+- `crates/ledger-core/tests/bookspec.rs` is the wanderbooks adapter: it
+  implements `Engine` over `Store` (a dev-dependency only, so no engine
+  crate depends on the specification) and remains the loader that checks
+  every figure. `ledger-package` answers the formats appendix's IIF
+  queries through the same adapter, as the package test does.
+
+Neither bookspec crate depends on `ledger-core`; the dependency points
+inward from the adapter. `just check` runs the bookspec workspace's
+format, clippy and tests beside the wanderbooks workspace's, so an example
+cannot rot (P13 step 1).