P3: the books' format moves only with the owner's go-ahead (D-39)

Books an update could write a newer format for open on their old format
and are asked at every open; anything needing a new feature is refused
until the owner agrees with the passphrase, after a verified backup that
includes the keys. New books start on the current format. Each projection
schema has its own database file, so an older version still opens the
books until the owner agrees.

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

crates/ledger-mcp/tests/spec_1099.rs

@@ -356,7 +356,25 @@ const CHART: &[(&str, &str, &str)] = &[
 
 /// Books with the chart; cash is 1000, financing 2100.
 fn books(name: &str) -> Mcp {
+    books_in(name, false)
+}
+
+/// [`books`], as P2 left them when `p2`: journal format 2 with none of
+/// P3's features, books an older version wrote, waiting for their format
+/// upgrade (rules.md B-27).
+fn books_in(name: &str, p2: bool) -> Mcp {
     let dir = test_dir(name);
+    if p2 {
+        ledger_store::Store::create_in_format(
+            &dir.join("books-data"),
+            ledger_core::Currency::USD,
+            &ledger_store::JournalFormat {
+                format: 2,
+                features: Vec::new(),
+            },
+        )
+        .unwrap();
+    }
     let toml = books_toml(&dir, "Spec Co", "financing_accounts = [\"2100\"]\n");
     let mut m = Mcp::start(&dir, &toml);
     m.accounts(CHART);
@@ -365,6 +383,23 @@ fn books(name: &str) -> Mcp {
 }
 
 impl Mcp {
+    /// The owner's go-ahead, as the app gives it (ledger-gui owner.rs,
+    /// after the passphrase and a verified backup; no tool can): the
+    /// server stopped, the books moved to this version's format, and
+    /// served again.
+    fn upgraded(mut self) -> Mcp {
+        let dir = self.books_dir.take().expect("books_dir");
+        drop(self);
+        ledger_store::Store::open(&dir.join("books-data"))
+            .unwrap()
+            .upgrade_format()
+            .unwrap()
+            .expect("P2's books wait for the upgrade");
+        let mut m = Mcp::start(&dir, &dir.join("wanderbooks.toml"));
+        m.books_dir = Some(dir);
+        m
+    }
+
     /// The same books, served again (a restart).
     fn restart(mut self) -> Mcp {
         let dir = self.books_dir.take().expect("books_dir");
@@ -553,7 +588,11 @@ fn set_vendor_1099_says_what_a_decision_needs() {
         assert!(why.contains(needle), "{args}: {why}");
     }
     assert_eq!(m.count("vendor.1099_set"), 0);
-    assert_eq!(m.count("journal.format_set"), 0, "nothing declared either");
+    assert_eq!(
+        m.count("journal.format_set"),
+        1,
+        "nothing declared either: only the books' own format, from their creation"
+    );
 }
 
 /// P3 brief 1.5 and review R8: tin_on_file omitted keeps the W-9 flag;
@@ -646,30 +685,37 @@ fn a_members_method_off_the_financing_accounts_warns() {
     assert!(out["warnings"].as_array().unwrap().is_empty(), "{out}");
 }
 
-/// B-27 and the format-upgrade gate (D-39): books.set_w9 on books that
-/// never used the vendor_1099_decisions feature journals the W-9 and then
-/// the vendor's W-9 flag, a line of that feature, so the feature is
-/// declared before the command's first line, never between its lines
-/// (where a refused upgrade would leave the W-9 recorded and the flag
-/// not).
+/// B-27 and the format-upgrade gate (D-39): books.set_w9 journals the W-9
+/// and then the vendor's W-9 flag, a line of the vendor_1099_decisions
+/// feature, so it asks for the feature before the command's first line,
+/// never between its lines. In books waiting for their format upgrade
+/// (P2's) the whole command is refused, journaling nothing (never the W-9
+/// recorded and the flag not); once the owner upgrades them, as in books
+/// this version made, it journals the W-9, then the flag, and declares
+/// nothing.
 #[test]
-fn set_w9_declares_the_w9_flags_feature_before_its_first_line() {
-    let mut m = books("set-w9-feature");
+fn set_w9_asks_for_the_w9_flags_feature_before_its_first_line() {
+    let w9 = json!({"party": "Harbor Design LLC", "received_on": "2026-03-02",
+                    "entity_type": "LLC (partnership)", "tin_last4": "4321", "kept_at": "CPA portal"});
+    let mut m = books_in("set-w9-feature", true);
     m.add_party("Harbor Design LLC", &["contractor"]);
     m.ok("books.add_vendor", json!({"name": "Harbor Design LLC"}));
-    let before = m.journal_types().len();
-    m.ok(
-        "books.set_w9",
-        json!({"party": "Harbor Design LLC", "received_on": "2026-03-02",
-               "entity_type": "LLC (partnership)", "tin_last4": "4321", "kept_at": "CPA portal"}),
+    let why = m.refuse("books.set_w9", w9.clone());
+    assert!(
+        why.starts_with("format_upgrade_pending:") && why.contains("vendor_1099_decisions"),
+        "{why}"
     );
-    let added = m.journal_types()[before..].to_vec();
-    assert_eq!(
-        added,
-        ["journal.format_set", "party.w9_set", "vendor.w9_flag_set"],
-        "the declaration comes first"
-    );
-    assert_eq!(decision(&mut m, "Harbor Design LLC")["tin_on_file"], true);
+    assert_eq!(m.count("party.w9_set"), 0, "nothing half done");
+    let mut fresh = books("set-w9-feature-new");
+    fresh.add_party("Harbor Design LLC", &["contractor"]);
+    fresh.ok("books.add_vendor", json!({"name": "Harbor Design LLC"}));
+    for mut m in [m.upgraded(), fresh] {
+        let before = m.journal_types().len();
+        m.ok("books.set_w9", w9.clone());
+        let added = m.journal_types()[before..].to_vec();
+        assert_eq!(added, ["party.w9_set", "vendor.w9_flag_set"]);
+        assert_eq!(decision(&mut m, "Harbor Design LLC")["tin_on_file"], true);
+    }
 }
 
 /// Defect 12 end to end, restarting between steps (P3 brief 8.2): payment