fix(banks): enforce unique bank display names in-model + B3 review minors

src/bank_book.cpp

@@ -77,6 +77,43 @@ void BankBook::normalizeOrdinals() {
         banks_[i].ordinal = static_cast<int>(i);
 }
 
+// ---------------------------------------------------------------------------
+// Display-name uniqueness (trimmed + case-insensitive, ASCII)
+// ---------------------------------------------------------------------------
+
+namespace {
+
+// Folds a display name to its uniqueness key: strip leading/trailing ASCII
+// whitespace, lower-case ASCII letters. So "Drums", "drums", and " Drums " share one
+// key and cannot coexist. ASCII-only by design — the pure core carries no locale
+// facility and must not grow one; bank names are short user labels, not full Unicode
+// case-folding candidates.
+std::string nameKey(const std::string& s) {
+    std::size_t b = 0, e = s.size();
+    auto isWs = [](char c) { return c == ' ' || c == '\t' || c == '\n' || c == '\r'; };
+    while (b < e && isWs(s[b])) ++b;
+    while (e > b && isWs(s[e - 1])) --e;
+    std::string out;
+    out.reserve(e - b);
+    for (std::size_t i = b; i < e; ++i) {
+        char c = s[i];
+        if (c >= 'A' && c <= 'Z') c = static_cast<char>(c - 'A' + 'a');
+        out += c;
+    }
+    return out;
+}
+
+}  // namespace
+
+// True if any bank OTHER than `exceptId` already carries `name`'s uniqueness key. The
+// exception lets renameBank accept a bank keeping (or re-casing/-spacing) its own name.
+bool BankBook::displayNameTaken(const std::string& name, const std::string& exceptId) const {
+    const std::string key = nameKey(name);
+    for (const auto& b : banks_)
+        if (b.id != exceptId && nameKey(b.displayName) == key) return true;
+    return false;
+}
+
 // ---------------------------------------------------------------------------
 // Bank lifecycle
 // ---------------------------------------------------------------------------
@@ -84,7 +121,10 @@ void BankBook::normalizeOrdinals() {
 bool BankBook::createBank(const std::string& id, const std::string& displayName) {
     if (id.empty()) return false;              // ids key the registry
     if (id == kPoolBankId) return false;       // reserved pool id
-    if (bank(id) != nullptr) return false;     // duplicate
+    if (bank(id) != nullptr) return false;     // duplicate id
+    // Display names are unique (trimmed + case-insensitive); the pool's "Pool" is a
+    // reserved name and is caught here like any other collision.
+    if (displayNameTaken(displayName, /*exceptId=*/id)) return false;
 
     Bank b;
     b.id = id;
@@ -99,6 +139,10 @@ bool BankBook::renameBank(const std::string& id, const std::string& displayName)
     if (id == kPoolBankId) return false;  // pool is un-renamable
     Bank* b = bank(id);
     if (b == nullptr) return false;
+    // Reject a name already used by a DIFFERENT bank. Renaming a bank to its own
+    // current name (or a case/space variant of it) is a no-op success, not a
+    // rejection — exceptId=id excludes the bank itself from the collision scan.
+    if (displayNameTaken(displayName, /*exceptId=*/id)) return false;
     b->displayName = displayName;
     return true;
 }