wallet: break the sweep/consolidation/autoshield deadlock

A successful-but-incomplete sweep round deliberately returns with fSweepRunning
still set and nextSweep unadvanced, as a "keep draining next block" baton. Every
early return in RunSaplingSweep, though, leaves that baton set without
re-dispatching -- and RunSaplingConsolidation, which is gated on fSweepRunning,
then returns without advancing nextConsolidation. So the "consolidation is
within 5 blocks" blackout at the top of RunSaplingSweep never lifts: sweep waits
on consolidation, consolidation waits on sweep, and neither runs again.

That much is pre-existing. What is new is that autoshield now shares the gate --
RunAutoShieldCoinbase returns early on fSweepRunning || fConsolidationRunning --
so a wedged sweep silently disables coinbase shielding too, with
z_autoshieldstatus reporting autoshield true, running false, and no reason.

Only honour the baton while a sweep operation is genuinely in flight: if the
operation for saplingSweepOperationId is absent or has reached a terminal state,
drop the stale flag and let the checks below decide afresh. The drain model is
unchanged -- nextSweep is still unadvanced, so the next block re-dispatches.

Also report the deferral in z_autoshieldstatus, so mutual exclusion with sweep
or consolidation reads as a deferral rather than an unexplained idle.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/wallet/rpcwallet.cpp

@@ -3408,6 +3408,12 @@ UniValue z_autoshieldstatus(const UniValue& params, bool fHelp, const CPubKey& m
             why = "disabled by -autoshield=0";
     } else if (pwalletMain->IsLocked()) {
         why = "wallet is locked; rounds are skipped until it is unlocked";
+    } else if (pwalletMain->fSweepRunning || pwalletMain->fConsolidationRunning) {
+        // Autoshield is mutually exclusive with sweep and consolidation. Without
+        // this the RPC reports autoshield=true, running=false and an empty
+        // reason while no round can actually start.
+        why = strprintf("deferred while %s is running; rounds resume when it finishes",
+                        pwalletMain->fSweepRunning ? "z_sweep" : "sapling consolidation");
     } else if (pwalletMain->autoShieldAddress.empty()) {
         why = "";
     }