mining: add submitBlock IPC method to Mining interface

diff --git a/src/interfaces/mining.h b/src/interfaces/mining.h
index a95bc220..ff4f8710 100644
--- a/src/interfaces/mining.h
+++ b/src/interfaces/mining.h
@@ -60,8 +60,10 @@ public:
      * @param[in] nonce nonce block header field
      * @param[in] coinbase complete coinbase transaction (including witness)
      *
-     * @note unlike the submitblock RPC, this method does NOT add the
-     *       coinbase witness automatically.
+     * @note Unlike the submitblock RPC, this method does not call
+     *       UpdateUncommittedBlockStructures to add a missing coinbase witness
+     *       reserved value. Callers must provide a complete coinbase transaction,
+     *       including the witness when a witness commitment is present.
      *
      * @note for heights <= 16, the BIP34 height push in getCoinbaseTx().script_sig_prefix
      *       is only one byte long, so the coinbase scriptSig needs at least
@@ -157,6 +159,27 @@ public:
      */
     virtual bool checkBlock(const CBlock& block, const node::BlockCheckOptions& options, std::string& reason, std::string& debug) = 0;
 
+    /**
+     * Process a fully assembled block.
+     *
+     * Similar to the submitblock RPC. Accepts a complete block, validates
+     * it, and if accepted as new, processes it into chainstate. Accepted
+     * blocks may then be announced to peers through normal validation signals.
+     *
+     * @param[in]  block  the complete block to submit
+     * @param[out] reason failure reason (BIP22)
+     * @param[out] debug  more detailed rejection reason
+     * @returns           true if the block was accepted as a new block. Returns
+     *                    false and sets reason if the block is a duplicate or
+     *                    the validation result is inconclusive.
+     *
+     * @note Unlike the submitblock RPC, this method does not call
+     *       UpdateUncommittedBlockStructures to add a missing coinbase witness
+     *       reserved value. Callers must submit a fully formed block, including
+     *       the coinbase witness when a witness commitment is present.
+     */
+    virtual bool submitBlock(const CBlock& block, std::string& reason, std::string& debug) = 0;
+
     //! Get internal node context. Useful for RPC and testing,
     //! but not accessible across processes.
     virtual const node::NodeContext* context() { return nullptr; }
diff --git a/src/ipc/capnp/mining.capnp b/src/ipc/capnp/mining.capnp
index 64cad4d4..a6dd8d71 100644
--- a/src/ipc/capnp/mining.capnp
+++ b/src/ipc/capnp/mining.capnp
@@ -25,6 +25,7 @@ interface Mining $Proxy.wrap("interfaces::Mining") {
     createNewBlock @4 (context :Proxy.Context, options: BlockCreateOptions, cooldown: Bool = true) -> (result: BlockTemplate);
     checkBlock @5 (context :Proxy.Context, block: Data, options: BlockCheckOptions) -> (reason: Text, debug: Text, result: Bool);
     interrupt @6 () -> ();
+    submitBlock @7 (context :Proxy.Context, block: Data) -> (reason: Text, debug: Text, result: Bool);
 }
 
 interface BlockTemplate $Proxy.wrap("interfaces::BlockTemplate") {
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index 28f8f2e8..2f68f414 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -1023,6 +1023,17 @@ public:
         return state.IsValid();
     }
 
+    bool submitBlock(const CBlock& block_in, std::string& reason, std::string& debug) override
+    {
+        auto block = std::make_shared<const CBlock>(block_in);
+        bool new_block;
+        const bool accepted = SubmitBlock(chainman(), block, &new_block, reason, debug);
+        // ProcessNewBlock() can accept and store a block before it is checked
+        // for validity. Treat duplicates as errors for mining clients, and only
+        // return success when validation completed without setting a reason.
+        return accepted && new_block && reason.empty();
+    }
+
     const NodeContext* context() override { return &m_node; }
     ChainstateManager& chainman() { return *Assert(m_node.chainman); }
     KernelNotifications& notifications() { return *Assert(m_node.notifications); }
diff --git a/src/test/miner_tests.cpp b/src/test/miner_tests.cpp
index 2ddc1307..fd9559b5 100644
--- a/src/test/miner_tests.cpp
+++ b/src/test/miner_tests.cpp
@@ -858,12 +858,20 @@ BOOST_AUTO_TEST_CASE(CreateNewBlock_validity)
             block.hashMerkleRoot = BlockMerkleRoot(block);
             block.nNonce = bi.nonce;
         }
-        std::shared_ptr<const CBlock> shared_pblock = std::make_shared<const CBlock>(block);
-        // Alternate calls between Chainman's ProcessNewBlock and submitSolution
-        // via the Mining interface. The former is used by net_processing as well
-        // as the submitblock RPC.
+        // Alternate calls between submitBlock and submitSolution via the
+        // Mining interface.
         if (current_height % 2 == 0) {
-            BOOST_REQUIRE(Assert(m_node.chainman)->ProcessNewBlock(shared_pblock, /*force_processing=*/true, /*min_pow_checked=*/true, nullptr));
+            std::string reason{"stale reason"};
+            std::string debug{"stale debug"};
+            BOOST_REQUIRE(mining->submitBlock(block, reason, debug));
+            BOOST_REQUIRE_EQUAL(reason, "");
+            BOOST_REQUIRE_EQUAL(debug, "");
+
+            reason = "stale reason";
+            debug = "stale debug";
+            BOOST_REQUIRE(!mining->submitBlock(block, reason, debug));
+            BOOST_REQUIRE_EQUAL(reason, "duplicate");
+            BOOST_REQUIRE_EQUAL(debug, "");
         } else {
             BOOST_REQUIRE(block_template->submitSolution(block.nVersion, block.nTime, block.nNonce, MakeTransactionRef(txCoinbase)));
         }