miner: bugfix: fix duplicate weight reservation in block assembler

- This commit renamed coinbase_max_additional_weight to block_reserved_weight.

- Also clarify that the reservation is for block header, transaction count
  and coinbase transaction.

src/node/miner.cpp

@@ -67,11 +67,11 @@ void RegenerateCommitments(CBlock& block, ChainstateManager& chainman)
 
 static BlockAssembler::Options ClampOptions(BlockAssembler::Options options)
 {
-    Assert(options.coinbase_max_additional_weight <= DEFAULT_BLOCK_MAX_WEIGHT);
+    Assert(options.block_reserved_weight <= MAX_BLOCK_WEIGHT);
     Assert(options.coinbase_output_max_additional_sigops <= MAX_BLOCK_SIGOPS_COST);
-    // Limit weight to between coinbase_max_additional_weight and DEFAULT_BLOCK_MAX_WEIGHT for sanity:
-    // Coinbase (reserved) outputs can safely exceed -blockmaxweight, but the rest of the block template will be empty.
-    options.nBlockMaxWeight = std::clamp<size_t>(options.nBlockMaxWeight, options.coinbase_max_additional_weight, DEFAULT_BLOCK_MAX_WEIGHT);
+    // Limit weight to between block_reserved_weight and MAX_BLOCK_WEIGHT for sanity:
+    // block_reserved_weight can safely exceed -blockmaxweight, but the rest of the block template will be empty.
+    options.nBlockMaxWeight = std::clamp<size_t>(options.nBlockMaxWeight, options.block_reserved_weight, MAX_BLOCK_WEIGHT);
     return options;
 }
 
@@ -97,8 +97,8 @@ void BlockAssembler::resetBlock()
 {
     inBlock.clear();
 
-    // Reserve space for coinbase tx
-    nBlockWeight = m_options.coinbase_max_additional_weight;
+    // Reserve space for fixed-size block header, txs count, and coinbase tx.
+    nBlockWeight = m_options.block_reserved_weight;
     nBlockSigOpsCost = m_options.coinbase_output_max_additional_sigops;
 
     // These counters do not include coinbase tx
@@ -386,7 +386,7 @@ void BlockAssembler::addPackageTxs(int& nPackagesSelected, int& nDescendantsUpda
             ++nConsecutiveFailed;
 
             if (nConsecutiveFailed > MAX_CONSECUTIVE_FAILURES && nBlockWeight >
-                    m_options.nBlockMaxWeight - m_options.coinbase_max_additional_weight) {
+                    m_options.nBlockMaxWeight - m_options.block_reserved_weight) {
                 // Give up if we're close to full and haven't succeeded in a while
                 break;
             }

src/node/types.h

@@ -14,6 +14,7 @@
 #define BITCOIN_NODE_TYPES_H
 
 #include <cstddef>
+#include <policy/policy.h>
 #include <script/script.h>
 
 namespace node {
@@ -34,11 +35,10 @@ struct BlockCreateOptions {
      */
     bool use_mempool{true};
     /**
-     * The maximum additional weight which the pool will add to the coinbase
-     * scriptSig, witness and outputs. This must include any additional
-     * weight needed for larger CompactSize encoded lengths.
+     * The default reserved weight for the fixed-size block header,
+     * transaction count and coinbase transaction.
      */
-    size_t coinbase_max_additional_weight{4000};
+    size_t block_reserved_weight{DEFAULT_BLOCK_RESERVED_WEIGHT};
     /**
      * The maximum additional sigops which the pool will add in coinbase
      * transaction outputs.