refactor: introduce SubmitBlock helper

diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index edb73628..28f8f2e8 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -920,7 +920,9 @@ public:
     bool submitSolution(uint32_t version, uint32_t timestamp, uint32_t nonce, CTransactionRef coinbase) override
     {
         AddMerkleRootAndCoinbase(m_block_template->block, std::move(coinbase), version, timestamp, nonce);
-        return chainman().ProcessNewBlock(std::make_shared<const CBlock>(m_block_template->block), /*force_processing=*/true, /*min_pow_checked=*/true, /*new_block=*/nullptr);
+        std::string reason;
+        std::string debug;
+        return SubmitBlock(chainman(), std::make_shared<const CBlock>(m_block_template->block), /*new_block=*/nullptr, reason, debug);
     }
 
     std::unique_ptr<BlockTemplate> waitNext(BlockWaitOptions options) override
diff --git a/src/node/miner.cpp b/src/node/miner.cpp
index 5c0df502..ccd9cc7c 100644
--- a/src/node/miner.cpp
+++ b/src/node/miner.cpp
@@ -38,6 +38,7 @@
 #include <util/time.h>
 #include <util/translation.h>
 #include <validation.h>
+#include <validationinterface.h>
 #include <versionbits.h>
 
 #include <algorithm>
@@ -357,6 +358,62 @@ void AddMerkleRootAndCoinbase(CBlock& block, CTransactionRef coinbase, uint32_t
     block.fChecked = false;
 }
 
+namespace {
+class SubmitBlockStateCatcher final : public CValidationInterface
+{
+public:
+    uint256 m_hash;
+    bool m_found{false};
+    BlockValidationState m_state;
+
+    explicit SubmitBlockStateCatcher(const uint256& hash) : m_hash{hash} {}
+
+protected:
+    void BlockChecked(const std::shared_ptr<const CBlock>& block, const BlockValidationState& state) override
+    {
+        if (block->GetHash() != m_hash) return;
+        // ProcessNewBlock emits BlockChecked synchronously while holding cs_main,
+        // so SubmitBlock can read these fields after ProcessNewBlock returns
+        // without extra synchronization.
+        m_found = true;
+        m_state = state;
+    }
+};
+} // namespace
+
+bool SubmitBlock(ChainstateManager& chainman, const std::shared_ptr<const CBlock>& block, bool* new_block, std::string& reason, std::string& debug)
+{
+    reason.clear();
+    debug.clear();
+
+    // This follows the submitblock RPC's validation-state capture pattern, but
+    // is intentionally kept separate from the RPC implementation. The RPC entry
+    // point decodes hex, formats BIP22/JSONRPC results, and calls
+    // UpdateUncommittedBlockStructures() for legacy witness handling. IPC
+    // callers submit already-formed blocks and need bool + reason/debug
+    // results, while submitSolution() preserves its duplicate-as-success
+    // behavior.
+    auto sc = std::make_shared<SubmitBlockStateCatcher>(block->GetHash());
+    CHECK_NONFATAL(chainman.m_options.signals)->RegisterSharedValidationInterface(sc);
+    bool accepted = chainman.ProcessNewBlock(block, /*force_processing=*/true, /*min_pow_checked=*/true, /*new_block=*/new_block);
+    CHECK_NONFATAL(chainman.m_options.signals)->UnregisterSharedValidationInterface(sc);
+
+    if (new_block && !*new_block && accepted) {
+        reason = "duplicate";
+    } else if (!sc->m_found) {
+        // A block can be accepted and stored without being connected, for
+        // example if it does not have more work than the current tip. In that
+        // case no BlockChecked callback is emitted, so the validation result is
+        // inconclusive. Mining::submitBlock treats this as an error for mining
+        // clients, but it does not mean the block is invalid.
+        reason = "inconclusive";
+    } else if (!sc->m_state.IsValid()) {
+        reason = sc->m_state.GetRejectReason();
+        debug = sc->m_state.GetDebugMessage();
+    }
+    return accepted;
+}
+
 void InterruptWait(KernelNotifications& kernel_notifications, bool& interrupt_wait)
 {
     LOCK(kernel_notifications.m_tip_block_mutex);
diff --git a/src/node/miner.h b/src/node/miner.h
index 14780833..af327307 100644
--- a/src/node/miner.h
+++ b/src/node/miner.h
@@ -18,6 +18,7 @@
 #include <cstdint>
 #include <memory>
 #include <optional>
+#include <string>
 #include <vector>
 
 class CBlockIndex;
@@ -129,6 +130,9 @@ void RegenerateCommitments(CBlock& block, ChainstateManager& chainman);
 /* Compute the block's merkle root, insert or replace the coinbase transaction and the merkle root into the block */
 void AddMerkleRootAndCoinbase(CBlock& block, CTransactionRef coinbase, uint32_t version, uint32_t timestamp, uint32_t nonce);
 
+//! Submit a block and capture the validation state via the BlockChecked callback.
+//! Returns whether ProcessNewBlock accepted the block.
+bool SubmitBlock(ChainstateManager& chainman, const std::shared_ptr<const CBlock>& block, bool* new_block, std::string& reason, std::string& debug);
 
 /* Interrupt a blocking call. */
 void InterruptWait(KernelNotifications& kernel_notifications, bool& interrupt_wait);