feat(migrate): persist the sweep opid so a mid-sweep interruption can resume (W3-3)

Migrate-to-seed submits z_mergetoaddress -> an async opid, then only persists the resolved
txid once the op completes. An app-close during Sweeping (opid submitted, txid not yet
resolved) dropped the opid and resumed at the re-sweep gate, silently losing the tx.

Now the opid is persisted and re-tracked on resume. If the daemon forgot it (restart —
its op queue is in-memory only), the existing poller flags it stale and the callback falls
back to the dismissable Sweep gate; it can never hang (a thrown RPC aborts the poll, so a
stale classification only comes from a *successful* poll that omits the opid).

- New seed_migration_sweep_opid setting; adopted atomically with clearing any prior txid in
  the SAME settings.save(), and only once the submit succeeds — so a failed "Sweep remaining"
  re-sweep keeps the already-mined first sweep's Confirming context, and txid/opid are never
  both authoritative (resume checks txid first; torn-write safe).
- Resume routing extracted to a pure, unit-tested helper
  (data/seed_migration_resume.h::decideSeedMigrationResume): txid -> Confirming; opid AND
  connected -> re-track (Sweeping); else -> the dismissable Sweep gate. The connectivity gate
  keeps a disconnected resume out of the buttonless Sweeping spinner.
- Shared makeSweepCompletionCallback(resumed): success -> Confirming; resumed-stale -> Sweep
  gate (re-fetch balance + "may have already completed" copy); fresh-fail -> Error.

Fund safety unchanged: adopt still gated on legacy balance ~0 AND sweep tx mined; legacy
wallet.dat only ever moved to a never-deleted timestamped .bak.

Reviewed in two adversarial rounds (design + implementation) per the migration-code mandate;
both safety facts (no fund loss, no hang) held, and the resume-UX traps they surfaced are
fixed. Build-clean; ctest 1/1 (adds testSeedMigrationResume). See docs/wallet-hardening.md.

*** Still requires a live mainnet interrupted-sweep run before release (human gate). ***

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

docs/wallet-hardening.md

@@ -18,7 +18,7 @@ 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-A** | W3-1, W3-2, W3-4, W3-3 ✓ | Migrate-to-seed correctness (fund-adjacent) | ☑ 4/4 (W3-3 pending a live-mainnet run) |
 | **P1-B** | W1-1, W1-2, W1-3, W1-4 ✓ + startup guard | Missing/wrong wallet-file safety | ☑ |
 | **P2**  | W5-1, W5-2, W6-1, W6-3, W6-2 ✓ | Stale state & lite save-failure surfacing | ☑ 5/5 |
 | **F**   | W7-2, W7-3, W7-4 ✓ · QoL: copy-diag + open-log + node-error-banner + staleness-badge + alert-history ✓ | Diagnostics foundation + QoL bundle | ☑ |
@@ -136,7 +136,11 @@ Land W7-2 first — it unblocks the rest.
   - **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-A / W3-3 (sweep opid persistence)** — ☑ **implemented + two rounds of adversarial review** (the "live mainnet run" the migration code mandates is the remaining gate — see below). The deferral's core fear (re-tracking a stale opid hangs forever) was **refuted by the code**: the opid poller (`app.cpp:1122`) + `parseOperationStatusPoll` classify a tracked opid absent from a *successful* `z_getoperationstatus` as stale, remove it, and fire the callback `ok=false` — a thrown RPC aborts the poll so there's never a *false* stale. So re-tracking yields at worst one clean failure, never a hang.
+  - **What landed:** a persisted `seed_migration_sweep_opid` setting; the opid is adopted **atomically** with clearing any prior txid in the *same* `settings.save()` **only once the submit succeeds** (torn-write safe; txid always outranks opid on resume). Resume routing is a pure, unit-tested helper (`data/seed_migration_resume.h::decideSeedMigrationResume`): txid → Confirming; opid **and connected** → re-track (`Sweeping`); otherwise → the dismissable Sweep gate. The shared `makeSweepCompletionCallback(resumed)`: success → Confirming; resumed-stale → Sweep gate (re-fetch balance, honest "may have already completed" copy); fresh-fail → Error.
+  - **Round 1 (design review, 4 skeptics)** confirmed both safety facts (no fund loss — adopt gate + never-deleted `.bak` untouched; no hang) and caught 3 real resume-UX traps, all fixed: a missing **connectivity gate** (would trap the user in the buttonless `Sweeping` spinner while offline), a **missing balance re-fetch** on the stale fallback (permanent "Checking balance…"), and honest messaging since a daemon restart makes even a *successful* sweep read "stale".
+  - **Round 2 (implementation review, 3 reviewers)** caught one regression — clearing the old txid at sweep *entry* would forget an already-mined first sweep if a remainder re-sweep's submit failed; fixed by the atomic-on-success swap above. All other fixes verified present + correct.
+  - **⚑ Remaining gate — live mainnet run (user):** per CLAUDE.md this fund-moving path must be exercised once on mainnet before it ships. The self-verifiable parts (build, unit test, both review rounds) are green; a real interrupted-sweep resume on mainnet is the human gate I cannot perform.
 - **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".