P3 review: P2 can read the books until the owner consents

A schedule-convention setting, the two new tax categories, a disposal
before the in-service date and a depreciation catch-up each need their
feature now (tax_categories_gain_exempt, disposal_before_service,
depreciation_catch_up), so no write before consent leaves books P2 refuses
or misreads; replayed names are read with P2's TIN detector (B-28). The
cutover runs end to end through the real P2 and P3 binaries in a test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-store/src/format.rs

@@ -56,6 +56,9 @@ pub const KNOWN_FEATURES: &[&str] = &[
     MONTH_REPOSTING,
     SCHEDULE_CONVENTION,
     ASSET_BASIS,
+    TAX_CATEGORIES_GAIN_EXEMPT,
+    DISPOSAL_BEFORE_SERVICE,
+    DEPRECIATION_CATCH_UP,
 ];
 
 /// Feature: `period.closed` closes to members with `"rounding":
@@ -75,13 +78,46 @@ pub const FEATURE_REQUIRE_TAX_CATEGORY: &str = "require_tax_category";
 
 /// The feature a `settings.set` naming `key` needs the books to have
 /// declared: a key an earlier version doesn't know.
+///
+/// Every key P3 added is one (P3 review, 2026-10-21: `books.schedule_convention`
+/// wasn't, so setting it left books P2 refuses to open, before consent).
 pub(crate) fn setting_feature(key: &str) -> Option<&'static str> {
     match key {
         "policy.require_tax_category" => Some(FEATURE_REQUIRE_TAX_CATEGORY),
+        "books.schedule_convention" => Some(SCHEDULE_CONVENTION),
         _ => None,
     }
 }
 
+/// Feature: an `account.tax_set` naming a tax category P3 added
+/// (`form_4797_gain_loss`, `tax_exempt_income`). An earlier version
+/// refuses the category, so it can't open the books (P3 review,
+/// 2026-10-21).
+pub const TAX_CATEGORIES_GAIN_EXEMPT: &str = "tax_categories_gain_exempt";
+
+/// The feature an `account.tax_set` naming `category` needs the books to
+/// have declared: a category an earlier version doesn't know.
+pub fn tax_category_feature(category: &str) -> Option<&'static str> {
+    match category {
+        "form_4797_gain_loss" | "tax_exempt_income" => Some(TAX_CATEGORIES_GAIN_EXEMPT),
+        _ => None,
+    }
+}
+
+/// Feature: an `asset.disposed` dated before the asset's in-service date
+/// (on or after the day it was acquired, P3 defect 13). An earlier version
+/// refuses a disposal before its `purchase_date`, so it can't open the
+/// books (P3 review, 2026-10-21).
+pub const DISPOSAL_BEFORE_SERVICE: &str = "disposal_before_service";
+
+/// Feature: an `asset.depreciation_posted` whose amount is not its month's
+/// own depreciation: earlier months skipped or reversed caught up in it, or
+/// a final month left over past the life (P3's run rule, B-15). An earlier
+/// version reads every run as its month's own: it would show the caught-up
+/// months as not yet run, and running them post their depreciation twice
+/// (P3 review, 2026-10-21).
+pub const DEPRECIATION_CATCH_UP: &str = "depreciation_catch_up";
+
 /// The feature `party.creditor_set` lines need: a party named the
 /// creditor of a liability (rules.md B-35, P3 defect 24).
 pub const PARTY_CREDITORS: &str = "party_creditors";
@@ -883,4 +919,101 @@ mod tests {
             other => panic!("expected NewerJournal, got {other:?}"),
         }
     }
+
+    /// The setting keys and tax categories P2 (9c99a0cf, the last version
+    /// before P3) read: a `settings.set` or `account.tax_set` naming any
+    /// other makes P2 refuse the books, so each other needs a feature
+    /// (P3 review, 2026-10-21: `books.schedule_convention` and two tax
+    /// categories didn't have one).
+    const P2_SETTING_KEYS: &[&str] = &[
+        "company.name",
+        "company.entity_type",
+        "company.tax_classification",
+        "company.tax_form",
+        "company.fiscal_year_start",
+        "company.timezone",
+        "company.formation_state",
+        "company.formed",
+        "company.state_entity_number",
+        "company.ein",
+        "company.irs_name_control",
+        "company.duns",
+        "company.address",
+        "company.registered_agent",
+        "company.partnership_representative",
+        "company.cpa",
+        "company.members",
+        "books.accounting_basis",
+        "books.cash_accounts",
+        "books.financing_accounts",
+        "books.investing_accounts",
+        "books.close_into",
+        "books.close_sweep",
+        "books.asset_tag_prefix",
+        "policy.evidence.threshold",
+        "policy.evidence.required_accounts",
+        "policy.evidence.exempt_accounts",
+        "policy.parties",
+        "policy.approval_rules",
+        "backup.git_remote",
+        "backup.folder",
+    ];
+    const P2_TAX_CATEGORIES: &[&str] = &[
+        "gross_receipts",
+        "returns_allowances",
+        "interest_income",
+        "other_income",
+        "cost_of_goods_sold",
+        "advertising",
+        "bad_debts",
+        "car_truck",
+        "charitable_contributions",
+        "commissions_fees",
+        "contract_labor",
+        "depreciation",
+        "employee_benefits",
+        "guaranteed_payments",
+        "insurance",
+        "interest_expense",
+        "legal_professional",
+        "meals",
+        "office_expense",
+        "officer_compensation",
+        "organization_startup",
+        "pension_profit_sharing",
+        "rent_equipment",
+        "rent_property",
+        "repairs",
+        "salaries_wages",
+        "supplies",
+        "taxes_licenses",
+        "travel",
+        "utilities",
+        "other_deductions",
+        "nondeductible",
+    ];
+
+    #[test]
+    fn every_setting_key_and_tax_category_p2_didnt_read_needs_a_feature() {
+        for k in ledger_core::settings::KEYS {
+            let known = P2_SETTING_KEYS.contains(&k.name);
+            assert_eq!(
+                setting_feature(k.name).is_none(),
+                known,
+                "{}: P2 {} it",
+                k.name,
+                if known { "reads" } else { "refuses" }
+            );
+        }
+        for c in ledger_core::tax::CATEGORIES {
+            let known = P2_TAX_CATEGORIES.contains(&c.key);
+            assert_eq!(tax_category_feature(c.key).is_none(), known, "{}", c.key);
+        }
+        for f in [
+            setting_feature("books.schedule_convention"),
+            tax_category_feature("tax_exempt_income"),
+        ] {
+            assert!(KNOWN_FEATURES.contains(&f.unwrap()));
+        }
+    }
 }

crates/ledger-store/src/store.rs

@@ -1137,6 +1137,11 @@ impl Store {
         })?;
         self.ledger
             .check_tax_category_required(code, name, account_type, placeholder, category)?;
+        // A category an earlier version doesn't know needs its feature:
+        // asked before the account's first line, never between the two.
+        if let Some(f) = category.and_then(crate::format::tax_category_feature) {
+            self.ensure_feature(f)?;
+        }
         let id =
             self.journal_account_added(code, name, account_type, parent, placeholder, |l| {
                 l.add_account(code, name, account_type, parent, placeholder)
@@ -2045,6 +2050,11 @@ impl Store {
         if self.depreciation_period_was_run(asset_id, period) {
             self.ensure_feature(crate::format::MONTH_REPOSTING)?;
         }
+        // More or less than the month's own (another month caught up in
+        // it): a run an earlier version would read as the month's own.
+        if amount != due.scheduled {
+            self.ensure_feature(crate::format::DEPRECIATION_CATCH_UP)?;
+        }
         let entry_id = self.create_entry(period_end, &description)?;
         self.add_line(entry_id, asset.expense_account, Side::Debit, money)?;
         self.add_line(entry_id, asset.accum_depr_account, Side::Credit, money)?;
@@ -2517,6 +2527,13 @@ impl Store {
         if depreciation.is_some() && self.depreciation_period_was_run(asset_id, &preview.period) {
             self.ensure_feature(crate::format::MONTH_REPOSTING)?;
         }
+        // Disposed before it was placed in service (acquired, not yet in
+        // use): an earlier version refuses that line (its floor was the
+        // in-service date), so it needs its feature, asked here, before
+        // the first line.
+        if date < asset.in_service_date {
+            self.ensure_feature(crate::format::DISPOSAL_BEFORE_SERVICE)?;
+        }
         if let Some((description, lines)) = &depreciation {
             let eid = self.create_entry(date, description)?;
             for (account, side, amount) in lines {
@@ -3806,6 +3823,9 @@ impl Store {
     ) -> Result<(), StoreError> {
         self.ledger
             .check_account_tax(account, category, deductible_percent)?;
+        if let Some(f) = category.and_then(crate::format::tax_category_feature) {
+            self.ensure_feature(f)?;
+        }
         let line = self.append_journal(
             "account.tax_set",
             json!({
@@ -5484,10 +5504,24 @@ fn get_str<'a>(p: &'a Value, key: &str) -> Result<&'a str, StoreError> {
 /// Replay one journal line into a ledger, asserting recorded ids. Used by
 /// hydration, `verify`, and `rebuild`: the journal is the script, the engine
 /// is the actor.
+///
+/// A full TIN is found as the version before P3 found one
+/// (`ledger_core::parties::replaying`): a name, reason or fact an earlier
+/// version took replays, however the commands' detector has widened since
+/// (rules.md B-28).
 pub(crate) fn replay_line_into_ledger(
     ledger: &mut Ledger,
     line: &JournalLine,
     base_currency: Currency,
+) -> Result<(), StoreError> {
+    ledger_core::parties::replaying(|| replay_line(ledger, line, base_currency))
+}
+
+/// [`replay_line_into_ledger`]'s work.
+fn replay_line(
+    ledger: &mut Ledger,
+    line: &JournalLine,
+    base_currency: Currency,
 ) -> Result<(), StoreError> {
     let p = &line.payload;
     match line.line_type.as_str() {