fix(wallet-switch): close gaps found verifying clusters A/B/C

Adversarial verification of the audit fixes found real gaps in them:

- HIGH throw-safety: the switch worker and the encryption-restart worker set
  daemon_restarting_=true but reset it only on their normal/early-return paths —
  a throw from stop/startEmbeddedDaemon left the flag stuck true, wedging
  reconnect and every future switch/rescan/encryption. Both now reset it on all
  paths (try/catch); a throw during a switch is treated as a failed switch and
  triggers the revert.
- HIGH residual chat leak: resetChatSession() cleared the flags but an already-
  posted z_exportmnemonic worker job still held wallet A's secret, and its
  completion callback (guarded only by isLocked(), false for an unencrypted
  wallet) would provision A's identity under B. Add a chat_session_generation_
  epoch bumped on every wallet change; the fetch captures it and its callback
  discards the (previous-wallet) secret if the epoch no longer matches.
- LOW vault-scope collision: the per-wallet vault tag was a lossy char-substitution
  (two distinct files could map to one vault). Append an 8-hex FNV-1a of the raw
  filename so distinct wallets never share a vault. +unit test.
- LOW seed-adopt: removeVault() on adopt so the legacy wallet's PIN passphrase
  isn't left associated with the new seed wallet (same file name).
- LOW: clear lock_unlock_in_progress_ on switch too.

Deferred (documented): the 1.5s start grace can't catch a wallet that fails LATE
in daemon init (the existing crash-wedge detection still applies); beginShutdown's
join of the switch task can briefly freeze the UI during quit (necessary to avoid
orphaning the daemon).

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

src/util/secure_vault.cpp

@@ -10,6 +10,7 @@
 #include <fstream>
 #include <filesystem>
 #include <cctype>
+#include <cstdio>
 #include <cstring>
 #include <algorithm>
 #include "../util/logger.h"
@@ -45,13 +46,20 @@ SecureVault::~SecureVault() = default;
 
 void SecureVault::setWalletScope(const std::string& walletFile) {
     // The default wallet keeps the legacy global "vault.dat" (empty scope) for backward compatibility;
-    // any other wallet gets a filesystem-safe per-wallet tag so its vault is separate.
+    // any other wallet gets a per-wallet tag. A readable sanitized prefix PLUS an 8-hex FNV-1a of the
+    // RAW filename — the hash disambiguates so two distinct files can never share a vault even if their
+    // sanitized forms collide (e.g. "wallet foo.dat" vs "wallet_foo.dat").
     if (walletFile.empty() || walletFile == "wallet.dat") { scope_.clear(); return; }
     std::string s;
     s.reserve(walletFile.size());
     for (unsigned char c : walletFile)
         s += (std::isalnum(c) || c == '-' || c == '_') ? static_cast<char>(c) : '_';
-    scope_ = s;
+    uint64_t h = 1469598103934665603ULL;                       // FNV-1a of the raw name
+    for (unsigned char c : walletFile) { h ^= c; h *= 1099511628211ULL; }
+    char suffix[9];
+    std::snprintf(suffix, sizeof(suffix), "%08x", static_cast<unsigned>(h & 0xffffffffu));
+    if (s.size() > 48) s.resize(48);
+    scope_ = s + "-" + suffix;
 }
 
 std::string SecureVault::getVaultPath() const {