fix(wallet): stamp syncedHere only after identity verified + guard the startup wallet file (W1-3)

- W1-3 (Med): updateWalletIndexForActiveWallet stamped syncedHere in the markOpened block
  at bare connect (idHash still empty), letting a freshly-restored wallet skip its needed
  rescan. syncedHere is now stamped only once the wallet's identity is verified (idHash
  non-empty), so it takes effect at the post-address-refresh index update; lastOpenedEpoch
  still records at open.

- Startup guard (the W1-1 launch counterpart): App::init now exists()-checks the recorded
  active wallet before the daemon is configured. A non-default active wallet moved/deleted
  between sessions falls back to the default wallet.dat with a warning, instead of the
  daemon silently auto-creating an empty wallet under the missing name. Runs before the PIN
  vault init so the vault is scoped to the wallet actually opened.

Completes P1-B. Remaining P1: W3-3 (sweep opid persistence) deferred for careful
adversarially-reviewed work — re-tracking a stale opid could hang the migration if the op
poller doesn't time out; the existing balance/mined gates already prevent fund loss. See
docs/wallet-hardening.md.

Build-clean; ctest 1/1.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/wallet-hardening.md

@@ -18,8 +18,8 @@ Status legend: ☐ not started · ◐ in progress · ☑ landed & verified
 |-------|----------|-------|--------|
 | **P0-A** | W7-1, W2-1, W4-1, W4-3, W2-3, W4-5, W5-3 ✓ | Secret hardening (console redaction + delete-export + memzero + lite encrypt-at-create) | ☑ 7/7 |
 | **P0-B** | W2-2/W4-2, W2-4 | Encryption integrity (never silently unencrypted) | ☑ |
-| **P1-A** | W3-1, W3-2, W3-4 ✓ · W3-3 ☐ | Migrate-to-seed correctness (fund-adjacent) | ◐ 3/4 |
-| **P1-B** | W1-1, W1-2, W1-4 ✓ · W1-3 ☐ | Missing/wrong wallet-file safety | ◐ 3/4 |
+| **P1-A** | W3-1, W3-2, W3-4 ✓ · W3-3 ⚑ | Migrate-to-seed correctness (fund-adjacent) | ◐ 3/4 |
+| **P1-B** | W1-1, W1-2, W1-3, W1-4 ✓ + startup guard | Missing/wrong wallet-file safety | ☑ |
 | **P2**  | W6-2, W5-1, W5-2, W6-1, W6-3 | Stale state & lite save-failure surfacing | ☐ |
 | **F**   | W7-2, W7-3, W7-4, QoL | Diagnostics foundation + QoL bundle | ☐ |
 
@@ -112,6 +112,11 @@ Land W7-2 first — it unblocks the rest.
 
 ## Progress log
 
+- **P1-B / W1-3 + startup wallet-existence guard** — ☑ landed:
+  - **W1-3 (Med):** `syncedHere` was stamped in the `markOpened` block at bare connect (idHash still empty), letting a freshly-restored wallet skip its needed rescan. It's now stamped only once the identity is verified (idHash non-empty), so it takes effect at the post-address-refresh index update (`updateWalletIndexForActiveWallet` after addresses load), while `lastOpenedEpoch` still records at open.
+  - **Startup guard (the W1-1 launch counterpart):** `App::init` now `exists()`-checks the recorded active wallet before the daemon is configured; a **non-default** active wallet that was moved/deleted between sessions falls back to the default `wallet.dat` with a warning, instead of the daemon silently auto-creating an empty wallet under the missing name. Runs before the PIN-vault init so the vault is scoped to the wallet actually opened.
+  Build-clean; `ctest` 1/1.
+- **P1-A / W3-3 (sweep opid persistence)** — ⚑ **deferred for careful, adversarially-reviewed work** (not rushed). `trackOperation` only enqueues the opid for a background poller; a resume that re-tracks a persisted opid is only safe if the poller times out a *stale* opid (daemon restarted → op gone) rather than polling forever — otherwise a resume would hang the migration permanently, worse than today's re-sweep. Verifying that (and the double-sweep interactions) is exactly the "two rounds of adversarial review + a live mainnet run" the migration code mandates. The existing safety gates (adopt requires the legacy balance ~0 AND the sweep tx mined) already prevent fund *loss* on a mid-sweep interruption; W3-3 is a stuck-state robustness improvement, so it can wait for a dedicated pass.
 - **P1-B / W1-1 (+ W1-4) · W1-2 (wallet-file safety)** — ☑ landed:
   - **W1-1 (High):** `switchToWallet` never checked the target wallet file exists, so a moved/deleted file "opened" as a fresh empty wallet (dragonxd auto-creates for a missing `-wallet=`), looking exactly like fund loss. It now `std::filesystem::exists`-checks `datadir + "/" + walletFile` before switching and blocks with a "not found (moved or deleted?)" warning. Placed before the daemon-stop prompt, and — since the check runs no matter how `switchToWallet` is invoked — it also **closes W1-4** (the stale-switcher-row TOCTOU).
   - **W1-2 (Med):** `walletOutputLooksCorrupt` matched the generic "Error loading wallet" string, so a `DB_TOO_NEW` (newer-version) wallet was offered a `-salvagewallet` repair that can't fix it. Now the generic match is excluded when the output also contains "newer version".