wallet: add default-on auto-shield-coinbase; drain miner coinbase into a z-addr

On this ac_private=1 chain miners accumulate one transparent coinbase UTXO per
block (the only transparent output the chain permits). It had to be shielded
manually via z_shieldcoinbase, and left unshielded it is the sole persistent
metadata leak on the chain and the source of miner UTXO-fragmentation send
failures.

Add AsyncRPCOperation_autoshieldcoinbase: a periodic, default-on wallet op
driven from CWallet::ChainTip alongside sweep/consolidation, draining matured
coinbase into a wallet-owned Sapling z-address in size-bounded batches.

- Enqueue-only driver (RunAutoShieldCoinbase): takes only cs_wallet in the
  notify context; all gathering runs on the async worker under LOCK2(cs_main,
  cs_wallet).
- Dedicated op (not a reuse of z_shieldcoinbase) so it never toggles mining.
- Default-ON but conditional: silent no-op on -disablewallet, external
  -mineraddress, non-mining, or locked wallets (explicit IsLocked() guard).
- Destination is reuse-then-create; -autoshieldaddress override is
  spend-key-validated at init so funds cannot be stranded.
- Sweep-model bookkeeping: advances nextAutoShield and clears the running flag
  on every terminal state; an op-id guard stops a stale op clobbering scheduler
  state; a self-guard stops cancel/re-enqueue churn.
- Sietch-padded output shape matches manual z_shieldcoinbase txns.

Config: -autoshield (default true), -autoshieldinterval, -autoshieldaddress,
-autoshieldfee (range-validated), -autoshieldminutxos.

Incorporates fixes from an 8-angle code review: CAmount fee type with init-time
range validation, op-id-guarded flag bookkeeping, driver self-guard, and a
tipHeight-consistent NU-activation guard.

Note: the fConsolidationRunning / nextConsolidation consolidation-scheduler
wedge is a pre-existing bug, left for a separate change.

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

src/Makefile.am

@@ -243,6 +243,7 @@ BITCOIN_CORE_H = \
   wallet/asyncrpcoperation_mergetoaddress.h \
   wallet/asyncrpcoperation_saplingconsolidation.h \
   wallet/asyncrpcoperation_sweep.h \
+  wallet/asyncrpcoperation_autoshieldcoinbase.h \
   wallet/asyncrpcoperation_sendmany.h \
   wallet/asyncrpcoperation_shieldcoinbase.h \
   wallet/crypter.h \
@@ -321,6 +322,7 @@ libbitcoin_wallet_a_SOURCES = \
   wallet/asyncrpcoperation_mergetoaddress.cpp \
   wallet/asyncrpcoperation_saplingconsolidation.cpp \
   wallet/asyncrpcoperation_sweep.cpp \
+  wallet/asyncrpcoperation_autoshieldcoinbase.cpp \
   wallet/asyncrpcoperation_sendmany.cpp \
   wallet/asyncrpcoperation_shieldcoinbase.cpp \
   wallet/crypter.cpp \

src/init.cpp

@@ -489,6 +489,12 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-zsweepexternal", _("Enable sweeping to an external wallet (default false)"));
     strUsage += HelpMessageOpt("-zsweepexclude", _("Addresses to exclude from sweeping (default none)"));
 
+    strUsage += HelpMessageOpt("-autoshield", _("Automatically shield matured coinbase (mining rewards) into a wallet z-address (default: true). No-op when not mining or wallet is locked."));
+    strUsage += HelpMessageOpt("-autoshieldinterval", strprintf(_("Block interval between automatic coinbase-shielding rounds (default: %i, min 5)"), 25));
+    strUsage += HelpMessageOpt("-autoshieldaddress=<zaddr>", _("Destination Sapling z-address for auto-shielded coinbase (default: reuse or create a wallet z-address). Must be spendable by this wallet."));
+    strUsage += HelpMessageOpt("-autoshieldfee", strprintf(_("Fee in puposhis for automatic coinbase-shielding transactions (default: %i)"), 10000));
+    strUsage += HelpMessageOpt("-autoshieldminutxos", strprintf(_("Only auto-shield once at least this many matured coinbase UTXOs exist (default: %i)"), 1));
+
     strUsage += HelpMessageOpt("-deletetx", _("Enable Old Transaction Deletion"));
     strUsage += HelpMessageOpt("-deleteinterval", strprintf(_("Delete transaction every <n> blocks during inital block download (default: %i)"), DEFAULT_TX_DELETE_INTERVAL));
     strUsage += HelpMessageOpt("-keeptxnum", strprintf(_("Keep the last <n> transactions (default: %i)"), DEFAULT_TX_RETENTION_LASTTX));
@@ -2451,6 +2457,55 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
             }
         }
 
+        //Set Automatic Coinbase Shielding (default ON, conditional: self-guards
+        //on nodes where it cannot act - no owned coinbase, external mineraddress,
+        //or locked wallet). Closes the transparent-coinbase leak for miners.
+        pwalletMain->fAutoShieldEnabled = GetBoolArg("-autoshield", true);
+        if (pwalletMain->fAutoShieldEnabled) {
+            int autoShieldInterval = GetArg("-autoshieldinterval", 25);
+            if (autoShieldInterval < 5) {
+                fprintf(stderr,"%s: Invalid autoshield interval of %d < 5, setting to default of 25\n", __func__, autoShieldInterval);
+                autoShieldInterval = 25;
+            }
+            pwalletMain->autoShieldInterval = autoShieldInterval;
+            pwalletMain->nextAutoShield     = pwalletMain->autoShieldInterval + chainActive.Height();
+
+            // Validate the fee: floor it above the relay minimum and cap it to
+            // guard against a fat-finger (e.g. -autoshieldfee=5000000000) that
+            // would otherwise build an over-fee or malformed shield tx that
+            // fails mempool admission every round.
+            CAmount autoShieldFee = GetArg("-autoshieldfee", 10000);
+            const CAmount AUTOSHIELD_MIN_FEE = 1000;      // comfortably above minRelayTxFee for a small tx
+            const CAmount AUTOSHIELD_MAX_FEE = 10000000;  // 0.1 DRGX; no sane autoshield fee exceeds this
+            if (autoShieldFee < AUTOSHIELD_MIN_FEE || autoShieldFee > AUTOSHIELD_MAX_FEE) {
+                fprintf(stderr,"%s: -autoshieldfee=%lld out of range [%lld,%lld], using default 10000\n",
+                        __func__, (long long)autoShieldFee, (long long)AUTOSHIELD_MIN_FEE, (long long)AUTOSHIELD_MAX_FEE);
+                autoShieldFee = 10000;
+            }
+            pwalletMain->autoShieldFee      = autoShieldFee;
+            pwalletMain->autoShieldMinUtxos = GetArg("-autoshieldminutxos", 1);
+            if (pwalletMain->autoShieldMinUtxos < 1) {
+                pwalletMain->autoShieldMinUtxos = 1;
+            }
+            LogPrintf("%s: autoshield enabled, nextAutoShield=%d interval=%d\n", __func__, pwalletMain->nextAutoShield, pwalletMain->autoShieldInterval);
+
+            //Optional explicit destination z-address. Must be a Sapling zaddr the
+            //wallet can spend, else the shielded coinbase would be unrecoverable.
+            std::string autoShieldAddress = GetArg("-autoshieldaddress", "");
+            if (!autoShieldAddress.empty()) {
+                auto zdest = DecodePaymentAddress(autoShieldAddress);
+                if (!IsValidPaymentAddress(zdest) ||
+                    boost::get<libzcash::SaplingPaymentAddress>(&zdest) == nullptr) {
+                    return InitError("Invalid -autoshieldaddress: must be a Sapling z-address");
+                }
+                auto hasSpendingKey = boost::apply_visitor(HaveSpendingKeyForPaymentAddress(pwalletMain), zdest);
+                if (!hasSpendingKey) {
+                    return InitError("Wallet must hold the spending key of -autoshieldaddress (else shielded coinbase would be unrecoverable)");
+                }
+                pwalletMain->autoShieldAddress = autoShieldAddress;
+            }
+        }
+
         //Set Transaction Deletion Options
         fTxDeleteEnabled = GetBoolArg("-deletetx", false);
         fTxConflictDeleteEnabled = GetBoolArg("-deleteconflicttx", true);

src/wallet/asyncrpcoperation_autoshieldcoinbase.cpp

@@ -0,0 +1,315 @@
+// Copyright (c) 2016-2024 The Hush developers
+// Copyright (c) 2024-2026 The DragonX developers
+// Distributed under the GPLv3 software license, see the accompanying
+// file COPYING or https://www.gnu.org/licenses/gpl-3.0.en.html
+#include "asyncrpcoperation_autoshieldcoinbase.h"
+#include "asyncrpcoperation_shieldcoinbase.h" // for ShieldCoinbaseUTXO
+#include "consensus/upgrades.h"
+#include "hush_defs.h" // ASSETCHAINS_TIMELOCKGTE
+#include "init.h"
+#include "key_io.h"
+#include "main.h"
+#include "rpc/protocol.h"
+#include "sync.h"
+#include "tinyformat.h"
+#include "transaction_builder.h"
+#include "util.h"
+#include "utilmoneystr.h"
+#include "wallet.h"
+
+// Sietch dummy zaddr generator (defined in wallet/rpcwallet.cpp)
+extern std::string randomSietchZaddr();
+
+// Serialized-size estimates for one spent input (kept in sync with rpcwallet.cpp)
+static const size_t AUTOSHIELD_CTXIN_DUST_SIZE = 148;
+static const size_t AUTOSHIELD_CTXIN_P2SH_SIZE = 400;
+// Expire unmined autoshield txs after this many blocks, so a tx cannot straddle
+// a network-upgrade activation.
+static const int AUTOSHIELD_EXPIRY_DELTA = 15;
+
+AsyncRPCOperation_autoshieldcoinbase::AsyncRPCOperation_autoshieldcoinbase(int targetHeight)
+    : targetHeight_(targetHeight) {}
+
+AsyncRPCOperation_autoshieldcoinbase::~AsyncRPCOperation_autoshieldcoinbase() {}
+
+void AsyncRPCOperation_autoshieldcoinbase::main() {
+    if (isCancelled()) {
+        // Only the CURRENT op owns the scheduler flag; a stale/cancelled op must
+        // not clear it out from under a freshly-enqueued successor.
+        if (pwalletMain) {
+            LOCK(pwalletMain->cs_wallet);
+            if (getId() == pwalletMain->saplingAutoShieldOperationId) {
+                pwalletMain->fAutoShieldRunning = false;
+            }
+        }
+        return;
+    }
+
+    set_state(OperationStatus::EXECUTING);
+    start_execution_clock();
+
+    bool success = false;
+
+    try {
+        success = main_impl();
+    } catch (const UniValue& objError) {
+        int code = find_value(objError, "code").get_int();
+        std::string message = find_value(objError, "message").get_str();
+        set_error_code(code);
+        set_error_message(message);
+    } catch (const runtime_error& e) {
+        set_error_code(-1);
+        set_error_message("runtime error: " + string(e.what()));
+    } catch (const logic_error& e) {
+        set_error_code(-1);
+        set_error_message("logic error: " + string(e.what()));
+    } catch (const exception& e) {
+        set_error_code(-1);
+        set_error_message("general exception: " + string(e.what()));
+    } catch (...) {
+        set_error_code(-2);
+        set_error_message("unknown error");
+    }
+
+    stop_execution_clock();
+
+    // ALWAYS advance the interval and clear the running flag, on success AND
+    // failure AND exception, so a failed/oversized/locked round still lets the
+    // next round fire. Only the CURRENT op does this bookkeeping: if a newer op
+    // has already superseded this one, leave its state untouched.
+    if (pwalletMain) {
+        LOCK2(cs_main, pwalletMain->cs_wallet);
+        if (getId() == pwalletMain->saplingAutoShieldOperationId) {
+            int tipHeight = (chainActive.Tip() != NULL) ? chainActive.Tip()->GetHeight() : targetHeight_;
+            pwalletMain->nextAutoShield    = pwalletMain->autoShieldInterval + tipHeight;
+            pwalletMain->fAutoShieldRunning = false;
+        }
+    }
+
+    set_state(success ? OperationStatus::SUCCESS : OperationStatus::FAILED);
+    setResult();
+
+    LogPrintf("%s: autoshield operation finished (status=%s, txs=%d, shielded=%s)\n",
+              getId(), getStateAsString(), numTxCreated_, FormatMoney(amountShielded_));
+}
+
+// Enumerate wallet-owned Sapling addresses and pick a spendable one; if none
+// exists, generate a fresh one (needs an unlocked wallet, which the caller has
+// already ensured). Caller must hold cs_wallet.
+bool AsyncRPCOperation_autoshieldcoinbase::resolveDestination(
+        libzcash::SaplingPaymentAddress& destOut, std::string& destStrOut) {
+
+    // 1. Explicit -autoshieldaddress override (validated + spend-key-checked at init)
+    if (!pwalletMain->autoShieldAddress.empty()) {
+        auto decoded = DecodePaymentAddress(pwalletMain->autoShieldAddress);
+        if (boost::get<libzcash::SaplingPaymentAddress>(&decoded) != nullptr) {
+            destOut    = boost::get<libzcash::SaplingPaymentAddress>(decoded);
+            destStrOut = pwalletMain->autoShieldAddress;
+            return true;
+        }
+        LogPrintf("%s: configured -autoshieldaddress is not a valid Sapling address\n", getId());
+        return false;
+    }
+
+    // 2. Reuse the first spendable wallet-owned Sapling address (std::set order
+    //    is deterministic, so this is stable across rounds/restarts).
+    std::set<libzcash::SaplingPaymentAddress> addrs;
+    pwalletMain->GetSaplingPaymentAddresses(addrs);
+    for (const auto& a : addrs) {
+        libzcash::SaplingExtendedSpendingKey extsk;
+        if (pwalletMain->GetSaplingExtendedSpendingKey(a, extsk)) {
+            destOut    = a;
+            destStrOut = EncodePaymentAddress(a);
+            // Cache it so we keep reusing the same address.
+            pwalletMain->autoShieldAddress = destStrOut;
+            return true;
+        }
+    }
+
+    // 3. No spendable z-addr yet: create one (requires unlocked wallet / HD seed).
+    if (pwalletMain->IsLocked()) {
+        return false;
+    }
+    try {
+        destOut    = pwalletMain->GenerateNewSaplingZKey();
+        destStrOut = EncodePaymentAddress(destOut);
+        pwalletMain->autoShieldAddress = destStrOut;
+        LogPrintf("%s: generated new autoshield destination z-address %s\n", getId(), destStrOut);
+        return true;
+    } catch (const std::exception& e) {
+        LogPrintf("%s: could not generate a destination z-address: %s\n", getId(), e.what());
+        return false;
+    }
+}
+
+bool AsyncRPCOperation_autoshieldcoinbase::main_impl() {
+    auto opid = getId();
+    LogPrintf("%s: Beginning asyncrpcoperation_autoshieldcoinbase.\n", opid);
+    auto consensusParams = Params().GetConsensus();
+
+    int tipHeight;
+    {
+        LOCK(cs_main);
+        tipHeight = (chainActive.Tip() != NULL) ? chainActive.Tip()->GetHeight() : targetHeight_;
+    }
+
+    // Don't create a tx that could be mined before, but expire after, a NU
+    // activation. Key this off tipHeight (the height we actually set the expiry
+    // from below), not the stale enqueue-time targetHeight_, so a queue delay
+    // cannot slip a straddling expiry past this guard.
+    auto nextActivationHeight = NextActivationHeight(tipHeight, consensusParams);
+    if (nextActivationHeight && tipHeight + AUTOSHIELD_EXPIRY_DELTA >= nextActivationHeight.get()) {
+        LogPrintf("%s: autoshield tx could expire across a NU activation. Skipping this round.\n", opid);
+        return true;
+    }
+
+    libzcash::SaplingPaymentAddress destZaddr;
+    std::string destStr;
+    std::vector<ShieldCoinbaseUTXO> inputs;
+    CAmount shieldedValue      = 0;
+    unsigned int max_tx_size   = MAX_TX_SIZE_AFTER_SAPLING;
+
+    {
+        LOCK2(cs_main, pwalletMain->cs_wallet);
+
+        // Defensive: the scheduler already skips while locked, but the wallet
+        // could have been locked between enqueue and execution.
+        if (pwalletMain->IsLocked()) {
+            LogPrintf("%s: wallet is locked, skipping autoshield round\n", opid);
+            return true;
+        }
+
+        if (!resolveDestination(destZaddr, destStr)) {
+            LogPrintf("%s: no spendable destination z-address available, skipping\n", opid);
+            return true;
+        }
+
+        // Gather matured, spendable coinbase UTXOs, byte-capped to a single tx.
+        // AvailableCoins with fOnlySpendable already excludes immature coinbase
+        // (< COINBASE_MATURITY) and outputs we don't own, so external
+        // -mineraddress / pool coinbase naturally yields zero inputs.
+        size_t estimatedTxSize = 2000; // header + sietch outputs headroom
+        std::vector<COutput> vecOutputs;
+        pwalletMain->AvailableCoins(vecOutputs, true, NULL, false, true);
+        for (const COutput& out : vecOutputs) {
+            if (!out.fSpendable || !out.tx->IsCoinBase()) {
+                continue;
+            }
+            CTxDestination address;
+            if (!ExtractDestination(out.tx->vout[out.i].scriptPubKey, address)) {
+                continue;
+            }
+            size_t increase = (boost::get<CScriptID>(&address) != nullptr)
+                                  ? AUTOSHIELD_CTXIN_P2SH_SIZE : AUTOSHIELD_CTXIN_DUST_SIZE;
+            if (estimatedTxSize + increase >= max_tx_size) {
+                // Size-safe batch; the remainder is shielded next round.
+                LogPrintf("%s: reached per-tx size cap; deferring remaining coinbase to next round\n", opid);
+                break;
+            }
+            estimatedTxSize += increase;
+            ShieldCoinbaseUTXO utxo = { out.tx->GetHash(), out.i,
+                                        out.tx->vout[out.i].scriptPubKey,
+                                        out.tx->vout[out.i].nValue };
+            inputs.push_back(utxo);
+            shieldedValue += out.tx->vout[out.i].nValue;
+        }
+    }
+
+    CAmount fee = pwalletMain->autoShieldFee;
+
+    if (inputs.size() < (size_t)pwalletMain->autoShieldMinUtxos) {
+        LogPrintf("%s: %d matured coinbase utxo(s) < min %d, skipping this round\n",
+                  opid, (int)inputs.size(), pwalletMain->autoShieldMinUtxos);
+        return true;
+    }
+    if (shieldedValue <= fee) {
+        LogPrintf("%s: matured coinbase value %s <= fee %s, skipping\n",
+                  opid, FormatMoney(shieldedValue), FormatMoney(fee));
+        return true;
+    }
+
+    // Common outgoing viewing key derived from the HD seed, exactly as
+    // z_shieldcoinbase does for t->z (keeps the note recoverable).
+    HDSeed seed;
+    if (!pwalletMain->GetHDSeedForDerivation(seed)) {
+        LogPrintf("%s: HD seed not available, skipping\n", opid);
+        return true;
+    }
+    uint256 ovk = ovkForShieldingFromTaddr(seed);
+
+    // Build the t->z shield tx. Proof generation happens in Build() WITHOUT
+    // holding cs_wallet (mirrors the sweep op) so we don't stall wallet RPCs.
+    auto builder = TransactionBuilder(consensusParams, targetHeight_, pwalletMain);
+    builder.SetExpiryHeight(tipHeight + AUTOSHIELD_EXPIRY_DELTA);
+    builder.SetFee(fee);
+
+    for (const auto& t : inputs) {
+        if (t.amount >= ASSETCHAINS_TIMELOCKGTE) {
+            builder.SetLockTime((uint32_t)tipHeight);
+            builder.AddTransparentInput(COutPoint(t.txid, t.vout), t.scriptPubKey, t.amount, 0xfffffffe);
+        } else {
+            builder.AddTransparentInput(COutPoint(t.txid, t.vout), t.scriptPubKey, t.amount);
+        }
+    }
+
+    // All input value (less fee) goes back to our own z-address as change.
+    builder.SendChangeTo(destZaddr, ovk);
+
+    // Sietch padding: mirror z_shieldcoinbase's two dummy zouts so autoshield
+    // txs are structurally indistinguishable from manual coinbase shields.
+    for (int i = 0; i < 2; i++) {
+        auto zdust = DecodePaymentAddress(randomSietchZaddr());
+        if (IsValidPaymentAddress(zdust)) {
+            builder.AddSaplingOutput(ovk, boost::get<libzcash::SaplingPaymentAddress>(zdust), 0);
+        }
+    }
+
+    auto maybe_tx = builder.Build();
+    if (!maybe_tx) {
+        LogPrintf("%s: Failed to build autoshield transaction.\n", opid);
+        return false;
+    }
+    CTransaction tx = maybe_tx.get();
+
+    if (isCancelled()) {
+        LogPrintf("%s: Cancelled before commit.\n", opid);
+        return false;
+    }
+
+    if (pwalletMain->CommitAutomatedTx(tx)) {
+        LogPrintf("%s: shielded %s coinbase (%d utxos) into %s via txid=%s\n",
+                  opid, FormatMoney(shieldedValue - fee), (int)inputs.size(),
+                  destStr, tx.GetHash().ToString());
+        amountShielded_ += shieldedValue - fee;
+        shieldTxIds_.push_back(tx.GetHash().ToString());
+        numTxCreated_++;
+        return true;
+    }
+
+    LogPrintf("%s: autoshield tx FAILED in CommitTransaction, txid=%s\n", opid, tx.GetHash().ToString());
+    return false;
+}
+
+void AsyncRPCOperation_autoshieldcoinbase::setResult() {
+    UniValue res(UniValue::VOBJ);
+    res.push_back(Pair("num_tx_created", numTxCreated_));
+    res.push_back(Pair("amount_shielded", FormatMoney(amountShielded_)));
+    UniValue txIds(UniValue::VARR);
+    for (const std::string& txId : shieldTxIds_) {
+        txIds.push_back(txId);
+    }
+    res.push_back(Pair("shield_txids", txIds));
+    set_result(res);
+}
+
+void AsyncRPCOperation_autoshieldcoinbase::cancel() {
+    set_state(OperationStatus::CANCELLED);
+}
+
+UniValue AsyncRPCOperation_autoshieldcoinbase::getStatus() const {
+    UniValue v = AsyncRPCOperation::getStatus();
+    UniValue obj = v.get_obj();
+    obj.push_back(Pair("method", "autoshieldcoinbase"));
+    obj.push_back(Pair("target_height", targetHeight_));
+    return obj;
+}

src/wallet/asyncrpcoperation_autoshieldcoinbase.h

@@ -0,0 +1,58 @@
+// Copyright (c) 2016-2024 The Hush developers
+// Copyright (c) 2024-2026 The DragonX developers
+// Distributed under the GPLv3 software license, see the accompanying
+// file COPYING or https://www.gnu.org/licenses/gpl-3.0.en.html
+#ifndef ASYNCRPCOPERATION_AUTOSHIELDCOINBASE_H
+#define ASYNCRPCOPERATION_AUTOSHIELDCOINBASE_H
+
+#include "amount.h"
+#include "asyncrpcoperation.h"
+#include "univalue.h"
+#include "zcash/Address.hpp"
+#include "zcash/zip32.h"
+
+// Default fee for automatic coinbase-shielding transactions
+static const CAmount DEFAULT_AUTOSHIELD_FEE = 10000;
+
+// A periodic, wallet-local operation that drains matured *transparent* coinbase
+// UTXOs into a wallet-owned Sapling z-address in size-bounded batches. It is the
+// automatic sibling of the manual z_shieldcoinbase RPC and mirrors the dispatch
+// model of AsyncRPCOperation_sweep (self-gathers on the async worker thread,
+// commits via CWallet::CommitAutomatedTx). It never mints a transparent output,
+// so it respects the ac_private=1 transparent-output ban, and it deliberately
+// does NOT toggle mining (unlike z_shieldcoinbase) so it can run every interval
+// on a mining node without thrashing the miner.
+class AsyncRPCOperation_autoshieldcoinbase : public AsyncRPCOperation
+{
+public:
+    AsyncRPCOperation_autoshieldcoinbase(int targetHeight);
+    virtual ~AsyncRPCOperation_autoshieldcoinbase();
+
+    // We don't want to be copied or moved around
+    AsyncRPCOperation_autoshieldcoinbase(AsyncRPCOperation_autoshieldcoinbase const&) = delete;
+    AsyncRPCOperation_autoshieldcoinbase(AsyncRPCOperation_autoshieldcoinbase&&) = delete;
+    AsyncRPCOperation_autoshieldcoinbase& operator=(AsyncRPCOperation_autoshieldcoinbase const&) = delete;
+    AsyncRPCOperation_autoshieldcoinbase& operator=(AsyncRPCOperation_autoshieldcoinbase&&) = delete;
+
+    virtual void main();
+    virtual void cancel();
+    virtual UniValue getStatus() const;
+
+private:
+    int targetHeight_;
+    int numTxCreated_        = 0;
+    CAmount amountShielded_  = 0;
+    std::vector<std::string> shieldTxIds_;
+
+    bool main_impl();
+
+    // Resolve a spendable, wallet-owned Sapling destination: the configured
+    // -autoshieldaddress if set, else the first spendable z-addr the wallet
+    // holds, else a freshly generated one (requires an unlocked wallet).
+    // Returns false if none is available (e.g. locked wallet with no z-addr).
+    bool resolveDestination(libzcash::SaplingPaymentAddress& destOut, std::string& destStrOut);
+
+    void setResult();
+};
+
+#endif /* ASYNCRPCOPERATION_AUTOSHIELDCOINBASE_H */

src/wallet/wallet.cpp

@@ -40,6 +40,7 @@
 #include "coins.h"
 #include "wallet/asyncrpcoperation_saplingconsolidation.h"
 #include "wallet/asyncrpcoperation_sweep.h"
+#include "wallet/asyncrpcoperation_autoshieldcoinbase.h"
 #include <random>
 #include <limits>
 #include <thread>
@@ -555,6 +556,9 @@ void CWallet::ChainTip(const CBlockIndex *pindex,
             if (fSweepEnabled) {
                 RunSaplingSweep(pindex->GetHeight());
             }
+            if (fAutoShieldEnabled) {
+                RunAutoShieldCoinbase(pindex->GetHeight());
+            }
             if (fTxDeleteEnabled) {
                 DeleteWalletTransactions(pindex);
             }
@@ -604,6 +608,12 @@ void CWallet::RunSaplingSweep(int blockHeight) {
         return;
     }
 
+    //Don't Run While auto-shield is running.
+    if (fAutoShieldRunning) {
+        LogPrintf("%s: not sweeping since autoshield is currently running at height=%d\n", __func__, blockHeight);
+        return;
+    }
+
     fSweepRunning = true;
 
     std::shared_ptr<AsyncRPCQueue> q = getAsyncRPCQueue();
@@ -641,6 +651,11 @@ void CWallet::RunSaplingConsolidation(int blockHeight) {
         return;
     }
 
+    if (fAutoShieldRunning) {
+        LogPrintf("%s: not consolidating since autoshield is currently running at height=%d\n", __func__, blockHeight);
+        return;
+    }
+
     LogPrintf("%s:  creating consolidation operation at blockHeight=%d\n", __func__,  blockHeight);
     std::shared_ptr<AsyncRPCQueue> q = getAsyncRPCQueue();
     std::shared_ptr<AsyncRPCOperation> lastOperation = q->getOperationForId(saplingConsolidationOperationId);
@@ -653,6 +668,63 @@ void CWallet::RunSaplingConsolidation(int blockHeight) {
     q->addOperation(operation);
 }
 
+// Periodically drain matured transparent coinbase into a wallet-owned Sapling
+// z-address. Default-ON but conditional: this is enqueue-only (all gathering
+// happens on the async worker thread inside the op, which is why we must not
+// take cs_main here — ChainTip runs from the wallet-notify context). It is a
+// silent no-op wherever it cannot act (locked wallet, no owned coinbase,
+// external -mineraddress), so it is safe to run on every node.
+void CWallet::RunAutoShieldCoinbase(int blockHeight) {
+    // Sapling is always active from height 1 on DragonX+HACs.
+    if (blockHeight == 0)
+        return;
+
+    LOCK(cs_wallet);
+
+    if (!fAutoShieldEnabled) {
+        return;
+    }
+
+    if (nextAutoShield > blockHeight) {
+        return;
+    }
+
+    // Self-guard: an op is already in flight (nextAutoShield only advances when
+    // it completes). Don't cancel + re-enqueue a fresh op every block.
+    if (fAutoShieldRunning) {
+        return;
+    }
+
+    // Mutual exclusion: sweep/consolidation share the single async worker and
+    // cs_wallet; don't queue an autoshield in the same connected block.
+    // NOTE: fConsolidationRunning is currently never set true (a pre-existing
+    // consolidation-scheduler bug); this half of the guard only becomes
+    // effective once that is fixed on the consolidation side.
+    if (fSweepRunning || fConsolidationRunning) {
+        LogPrintf("%s: not autoshielding since sweep/consolidation is running at height=%d\n", __func__, blockHeight);
+        return;
+    }
+
+    // Silent no-op while locked: we can neither sign the shield nor derive a
+    // destination z-addr. Advance the interval so we don't retry every block.
+    if (IsLocked()) {
+        LogPrintf("%s: wallet locked; matured coinbase will accumulate until unlocked (height=%d)\n", __func__, blockHeight);
+        nextAutoShield = autoShieldInterval + blockHeight;
+        return;
+    }
+
+    fAutoShieldRunning = true;
+
+    std::shared_ptr<AsyncRPCQueue> q = getAsyncRPCQueue();
+    std::shared_ptr<AsyncRPCOperation> lastOperation = q->getOperationForId(saplingAutoShieldOperationId);
+    if (lastOperation != nullptr) {
+        lastOperation->cancel();
+    }
+    std::shared_ptr<AsyncRPCOperation> operation(new AsyncRPCOperation_autoshieldcoinbase(blockHeight + 5));
+    saplingAutoShieldOperationId = operation->getId();
+    q->addOperation(operation);
+}
+
 bool CWallet::CommitAutomatedTx(const CTransaction& tx) {
   CWalletTx wtx(this, tx);
   CReserveKey reservekey(pwalletMain);

src/wallet/wallet.h

@@ -809,6 +809,12 @@ public:
     bool fSweepExternalEnabled        = false;
     bool fSweepRunning                = false;
 
+    // Automatic coinbase shielding (t->z). Default ON but conditional: it is a
+    // silent no-op on nodes where it cannot act (no wallet, external
+    // -mineraddress, non-mining, or locked wallet). See RunAutoShieldCoinbase.
+    bool fAutoShieldEnabled           = true;
+    bool fAutoShieldRunning           = false;
+
     std::atomic<bool> fAbortRescan{false};
     // abort current rescan
     void AbortRescan() { fAbortRescan = true; }
@@ -833,6 +839,19 @@ public:
     std::vector<std::string> sweepExcludeAddresses;
     std::string consolidationAddress  = "";
 
+    int nextAutoShield                = 0;
+    int autoShieldInterval            = 25;
+    CAmount autoShieldFee             = 10000;
+    // Minimum matured coinbase UTXOs before a round fires, to avoid per-interval
+    // fee churn on a single freshly-matured reward.
+    int autoShieldMinUtxos            = 1;
+    // Configured destination z-addr override; also used to cache the resolved
+    // wallet-owned destination so we keep reusing one address.
+    std::string autoShieldAddress     = "";
+    // Id of the in-flight autoshield op; read by the op to confirm it is still
+    // the current one before mutating scheduler state.
+    AsyncRPCOperationId saplingAutoShieldOperationId;
+
     void ClearNoteWitnessCache();
 
     int64_t NullifierCount();
@@ -1224,6 +1243,7 @@ public:
         const CBlock *pblock,
         boost::optional<std::pair<SproutMerkleTree, SaplingMerkleTree>> added);
     void RunSaplingConsolidation(int blockHeight);
+    void RunAutoShieldCoinbase(int blockHeight);
     bool CommitAutomatedTx(const CTransaction& tx);
     /** Saves witness caches and best block locator to disk. */
     void SetBestChain(const CBlockLocator& loc);