feat(chat): per-conversation delete (revive + block); memoize chat/badge render

Adds a per-conversation "delete" with two modes, and removes the per-frame
rescans of the chat history that shared these files.

Delete conversation (header trash icon → confirm dialog):
- Delete (revive-on-new-message): clears local history and tombstones the
  messages (new chat_deleted table, keyed dedup hashes) so the every-few-
  seconds memo re-scan can't re-import them; a genuinely NEW message (new
  txid) revives the thread.
- Delete & block: removes history WITHOUT a tombstone and records the cid as
  blocked (settings); ChatService::ingest drops that conversation's messages
  — old and future — until unblocked from the "Blocked" manager, which then
  re-imports the conversation from chain.
- Local-only (messages remain on-chain; the peer keeps their copy).
  deleteConversation() deletes the DB rows FIRST and only then mutates the
  store, so a failed write can't leave the two diverged.
Unit-tested (revive / tombstone-survives-reload / block / unblock) and
adversarially reviewed (store/DB divergence, half-open DB, revive-unread).

Performance (chat + badge hot paths, from the perf audit):
- ChatStore gains revision(); the Chat unread badge is now a single O(N)
  no-alloc pass cached on it (was O(conversations x messages) copy+sort every
  frame). The conversation list and open thread are memoized on revision()
  (+ show-hidden and AddressBook::revision() for peer-name resolution).
- AddressBook gains revision() so an in-place contact rename invalidates the
  chat memo (an edit keeps entries().size() constant).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/chat/chat_database.cpp

@@ -89,6 +89,7 @@ bool ChatDatabase::unlockWithSecret(const std::string& secret)
         lock();
         return false;
     }
+    loadTombstones();
     return true;
 }
 
@@ -97,11 +98,13 @@ void ChatDatabase::lock()
     sodium_memzero(key_.data(), key_.size());
     key_ready_ = false;
     wallet_tag_.clear();
+    tombstones_.clear();
 }
 
 bool ChatDatabase::append(const ChatMessage& message)
 {
     if (!key_ready_ || !ensureOpen()) return false;
+    if (isTombstoned(message)) return false;  // locally deleted — don't re-persist on a chain re-scan
 
     std::vector<unsigned char> nonce;
     std::vector<unsigned char> cipher;
@@ -193,13 +196,79 @@ std::vector<ChatMessage> ChatDatabase::load()
 void ChatDatabase::clearWallet()
 {
     if (wallet_tag_.empty() || !ensureOpen()) return;
+    for (const char* sql : {"DELETE FROM chat_messages WHERE wallet_tag = ?",
+                            "DELETE FROM chat_deleted WHERE wallet_tag = ?"}) {
+        sqlite3_stmt* stmt = nullptr;
+        if (sqlite3_prepare_v2(db_, sql, -1, &stmt, nullptr) != SQLITE_OK) continue;
+        sqlite3_bind_text(stmt, 1, wallet_tag_.c_str(), -1, SQLITE_TRANSIENT);
+        sqlite3_step(stmt);
+        sqlite3_finalize(stmt);
+    }
+    tombstones_.clear();
+}
+
+bool ChatDatabase::deleteMessages(const std::vector<ChatMessage>& messages, bool tombstone)
+{
+    if (!key_ready_ || !ensureOpen()) return false;
+    if (messages.empty()) return true;
+
+    if (!exec("BEGIN")) return false;
+    bool ok = true;
+    for (const auto& m : messages) {
+        const std::string dedup = dedupHash(m.txid, m.payload_position);
+
+        sqlite3_stmt* del = nullptr;
+        if (sqlite3_prepare_v2(db_, "DELETE FROM chat_messages WHERE wallet_tag = ? AND dedup_hash = ?",
+                               -1, &del, nullptr) == SQLITE_OK) {
+            sqlite3_bind_text(del, 1, wallet_tag_.c_str(), -1, SQLITE_TRANSIENT);
+            sqlite3_bind_text(del, 2, dedup.c_str(), -1, SQLITE_TRANSIENT);
+            if (sqlite3_step(del) != SQLITE_DONE) ok = false;
+            sqlite3_finalize(del);
+        } else {
+            ok = false;
+        }
+
+        if (tombstone) {
+            sqlite3_stmt* ins = nullptr;
+            if (sqlite3_prepare_v2(db_,
+                    "INSERT OR IGNORE INTO chat_deleted (wallet_tag, dedup_hash) VALUES (?, ?)",
+                    -1, &ins, nullptr) == SQLITE_OK) {
+                sqlite3_bind_text(ins, 1, wallet_tag_.c_str(), -1, SQLITE_TRANSIENT);
+                sqlite3_bind_text(ins, 2, dedup.c_str(), -1, SQLITE_TRANSIENT);
+                if (sqlite3_step(ins) != SQLITE_DONE) ok = false;
+                sqlite3_finalize(ins);
+            } else {
+                ok = false;
+            }
+        }
+    }
+    if (!exec(ok ? "COMMIT" : "ROLLBACK")) ok = false;
+    // Only reflect the tombstones in the in-memory cache once they are durably committed.
+    if (ok && tombstone)
+        for (const auto& m : messages) tombstones_.insert(dedupHash(m.txid, m.payload_position));
+    return ok;
+}
+
+bool ChatDatabase::isTombstoned(const ChatMessage& message) const
+{
+    if (!key_ready_ || tombstones_.empty()) return false;
+    return tombstones_.count(dedupHash(message.txid, message.payload_position)) > 0;
+}
+
+void ChatDatabase::loadTombstones()
+{
+    tombstones_.clear();
+    if (!key_ready_ || !ensureOpen()) return;
     sqlite3_stmt* stmt = nullptr;
-    if (sqlite3_prepare_v2(db_, "DELETE FROM chat_messages WHERE wallet_tag = ?", -1, &stmt, nullptr)
-        != SQLITE_OK) {
+    if (sqlite3_prepare_v2(db_, "SELECT dedup_hash FROM chat_deleted WHERE wallet_tag = ?",
+                           -1, &stmt, nullptr) != SQLITE_OK) {
         return;
     }
     sqlite3_bind_text(stmt, 1, wallet_tag_.c_str(), -1, SQLITE_TRANSIENT);
-    sqlite3_step(stmt);
+    while (sqlite3_step(stmt) == SQLITE_ROW) {
+        const auto* h = reinterpret_cast<const char*>(sqlite3_column_text(stmt, 0));
+        if (h) tombstones_.insert(h);
+    }
     sqlite3_finalize(stmt);
 }
 
@@ -260,11 +329,18 @@ bool ChatDatabase::exec(const char* sql)
 
 bool ChatDatabase::createSchema()
 {
-    return exec("CREATE TABLE IF NOT EXISTS chat_messages ("
+    if (!exec("CREATE TABLE IF NOT EXISTS chat_messages ("
+              "wallet_tag TEXT NOT NULL, "
+              "dedup_hash TEXT NOT NULL, "
+              "nonce BLOB NOT NULL, "
+              "payload BLOB NOT NULL, "
+              "PRIMARY KEY (wallet_tag, dedup_hash))"))
+        return false;
+    // Tombstones for locally-deleted messages (dedup_hash only — the same keyed, non-revealing hash the
+    // message rows use). A chain re-scan checks this so a deleted message never re-imports.
+    return exec("CREATE TABLE IF NOT EXISTS chat_deleted ("
                 "wallet_tag TEXT NOT NULL, "
                 "dedup_hash TEXT NOT NULL, "
-                "nonce BLOB NOT NULL, "
-                "payload BLOB NOT NULL, "
                 "PRIMARY KEY (wallet_tag, dedup_hash))");
 }