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/testing.md

@@ -2847,3 +2847,71 @@ nine-digit check), `full_tin_runs`'s `extend(grouped_tin_runs(..))`;
 Deleting any one of them leaves a TIN that the old scanner passed
 either readable or unmasked, which the truth table and the property
 catch.
+## P13: bookspec, the checker crate and the runner (2026-10-26)
+
+bookspec's example schema moved out of the loader into
+`bookspec/checker`, its own Cargo workspace inside the repository (P13
+step 1, D-34). `crates/ledger-core/tests/bookspec.rs` is now the
+wanderbooks adapter: it imports `Example`, `Setup`, `Event`, `Expect`,
+`Query`, `Refusal` and the rest from the checker by a path dev-dependency,
+and it is unchanged in what it proves. The loader parses every example
+with `Example::from_toml` (the parser plus the schema's own cross-field
+checks), so a malformed example fails before an engine sees it.
+
+Step 2 adds the `Engine` trait (`bookspec/checker/src/engine.rs`: `load`,
+`apply`, `query`, `claims`, and `change` for a `[[changes]]` entry), the
+runner (`bookspec/runner`), and the adapter's implementation over `Store`.
+The runner runs all 56 examples, one fresh engine each, compares every
+answer with the example's exact values and every refusal with the reason
+the example names, and reports per rule: pass, fail or not claimed. The
+adapter claims the rules the catalogue gives an example; a rule with no
+example is not claimed, never silently passed.
+
+Step 3 adds the rule identifiers: `BS-<area>-<n>` for the eleven areas,
+`bookspec/spec/rules-index.md` as the table from B-1 to B-45, and each
+stated rule's id under its heading in `docs/spec/rules.md`. `DECISION`
+there is bookspec's `CHOICE`: the specification names the options, an
+engine declares its pick (`Claims::with_choice`). B-39 to B-45 are
+allocated (`plan/served.md` 8.0.3) and not yet stated; they carry an id and
+an area and no status.
+
+- **`bookspec/checker` `tests/schema.rs`:** `every_seed_example_parses_and_validates`
+  (all 56, the file named for its id, ids unique), `an_unknown_key_is_refused`,
+  `the_status_is_authority_convention_or_choice`, `a_line_amount_is_exact_and_positive`,
+  `an_event_is_exactly_one_kind`, `reverses_counts_events_from_one`,
+  `the_members_shares_sum_to_one`, `a_share_is_a_fraction_above_zero`,
+  `every_refusal_reason_names_a_rule`, `an_unknown_query_is_refused`,
+  `a_period_may_be_refused`, `a_command_shows_no_values`,
+  `a_figure_query_takes_exact_decimals`, `a_query_does_not_carry_its_expected_values`,
+  `a_format_query_is_of_the_formats_appendix`, `the_rule_index_lists_every_stated_rule`.
+- **`bookspec/checker` `tests/rules.rs`:** `every_b_rule_has_one_id`,
+  `the_index_matches_the_catalogue`, `every_example_is_listed_under_a_rule`,
+  `a_claimed_rule_has_an_example`, `an_id_has_one_spelling`,
+  `a_choice_rule_declares_its_option`.
+- **`bookspec/checker` `tests/docs.rs`:** `rules_md_carries_every_id`.
+- **`bookspec/runner` `tests/runner.rs`:** `a_passing_engine_passes`,
+  `a_wrong_answer_fails`, `an_engine_that_claims_nothing_is_not_claimed`,
+  `a_claim_without_an_example_fails`, `a_refused_query_fails`,
+  `an_example_listed_under_no_rule_fails`, `a_refused_change_fails`. The
+  fake engine proves the runner judges answers, not the engine's belief.
+- **`ledger-core` `tests/bookspec.rs`:** `the_runner_reports_every_claimed_rule_green`
+  (all 56 examples through the trait, every claimed rule pass) and
+  `every_bookspec_example_holds` (unchanged: the loader's own checks).
+- **`ledger-package` `tests/package.rs`:** `the_bookspec_iif_example_matches_the_engine`
+  unchanged; the adapter answers the formats appendix through
+  `ledger_package::export_iif`, the same code the package test checks.
+
+**For P12 (mutation targets):** `rules::build`'s area ordinals (a rule in
+the wrong area); `RuleId::parse`'s prefix, area, digit, leading-zero and
+zero checks; `rule_for_refusal`'s mapping arms; `schema::is_exact_decimal`
+(each character class and the single point), `is_date`, `is_month`,
+`is_month_day` and `check_amount`'s positivity; `Example::validate`'s
+closed-list arms, the one-kind rule, `reverses < n`, the shares summing to
+1, `after` bounds, the command's accepted-or-refused exclusivity and the
+`only` table; `Query::is_complete`'s membership; `Refusal::of_reason`'s
+fallback; the runner's `compare` (key equality, missing and extra keys,
+list and row equality), `Outcome`'s mapping and `run`'s "claimed but no
+example" arm; the adapter's `event_of`, its `depreciation_schedule` month
+span (acquisition through as-of, 0.00 where the schedule reaches no month)
+and every `answer_*` figure against the loader's same check (the two must
+agree on all 56 examples).>>>>>>> 382e9406 (feat(bookspec): rule identifiers from B-1 to B-45 (P13))