Add dual SHA256D block check for pool mining mode

Pool sends block_target (full 256-bit network target) with each job.
Miner checks SHA256D(header + RandomX solution) for every hash against
the block target, enabling block detection at full hashrate instead of
only on submitted shares.

src/base/net/stratum/Job.cpp

@@ -115,6 +115,40 @@ bool xmrig::Job::setSeedHash(const char *hash)
 }
 
 
+bool xmrig::Job::setBlockTarget(const char *target)
+{
+    if (!target) {
+        m_hasBlockTarget = false;
+        return false;
+    }
+
+    const size_t len = strlen(target);
+    if (len != 64) {  // 32 bytes = 64 hex chars
+        m_hasBlockTarget = false;
+        return false;
+    }
+
+    // Parse 64-char hex string (display order) into uint256-compatible internal byte order.
+    // Display "00072f0f...000" → internal: data[31]=0x00, data[30]=0x07, data[29]=0x2f, ...
+    // This matches how Bitcoin/Zcash uint256 stores values (LSB at data[0], MSB at data[31]).
+    // Raw SHA256D output from OpenSSL also goes into uint256.data[] without reversal,
+    // so both hash and target are in the same internal byte order for comparison.
+    uint8_t tmp[32];
+    if (!Cvt::fromHex(tmp, sizeof(tmp), target, len)) {
+        m_hasBlockTarget = false;
+        return false;
+    }
+
+    // Reverse display order to internal byte order (LSB-first / little-endian uint256)
+    for (int i = 0; i < 32; ++i) {
+        m_blockTarget[i] = tmp[31 - i];
+    }
+
+    m_hasBlockTarget = true;
+    return true;
+}
+
+
 bool xmrig::Job::setTarget(const char *target)
 {
     static auto parse = [](const char *target, size_t size, const Algorithm &algorithm) -> uint64_t {
@@ -297,6 +331,9 @@ void xmrig::Job::copy(const Job &other)
 #   endif
 
     m_hasMinerSignature = other.m_hasMinerSignature;
+    m_hasBlockTarget = other.m_hasBlockTarget;
+    m_isSoloMining = other.m_isSoloMining;
+    memcpy(m_blockTarget, other.m_blockTarget, sizeof(m_blockTarget));
 }
 
 
@@ -353,6 +390,9 @@ void xmrig::Job::move(Job &&other)
 #   endif
 
     m_hasMinerSignature = other.m_hasMinerSignature;
+    m_hasBlockTarget = other.m_hasBlockTarget;
+    m_isSoloMining = other.m_isSoloMining;
+    memcpy(m_blockTarget, other.m_blockTarget, sizeof(m_blockTarget));
 }