feat(consensus): make block-1 premine mainnet-only so testnet can bootstrap

GetBlockValue(1) returned the 5,000,000 FAIR premine unconditionally, but
ConnectBlock validates a block's mint against GetBlockValue(prev_height) — so
for a brand-new chain, block 1 mints 5M while consensus expects the normal
reward at height 0, and the block is rejected ("reward pays too much"). Mainnet
is unaffected (its block 1 is long since mined and checkpointed), but it makes a
fresh testnet impossible to launch.

Gate the premine to non-testnet so testnet block 1 mints the normal subsidy and
is mineable. Mainnet consensus is byte-identical. release.yml marks *-testnet*
tags as prereleases so they never become releases/latest (tracked by mainnet).

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

Author: NateIsern

.github/workflows/release.yml

@@ -201,7 +201,9 @@ jobs:
         with:
           name: FairCoin ${{ github.ref_name }}
           draft: false
-          prerelease: false
+          # Mark *-testnet* tags as prereleases so they never become releases/latest
+          # (the mainnet node tracks releases/latest). Normal v* tags stay full releases.
+          prerelease: ${{ contains(github.ref_name, '-testnet') }}
           generate_release_notes: true
           fail_on_unmatched_files: false
           files: |

src/main.cpp

@@ -1617,8 +1617,14 @@ double ConvertBitsToDouble(unsigned int nBits)
 
 int64_t GetBlockValue(int nHeight)
 {
-    if (nHeight == 1)
-        return 5000000 * COIN; // premine on block 1 (block 0 coinbase is unspendable by protocol)
+    // Premine is a one-time mainnet launch event (block 0 coinbase is unspendable
+    // by protocol). It is mainnet-only: a fresh testnet must be bootstrappable, but
+    // the miner pays GetBlockValue(1) while ConnectBlock validates against
+    // GetBlockValue(prev=0)=normal subsidy, so a premined block 1 is rejected on a
+    // brand-new chain. Excluding testnet lets testnet block 1 mint the normal reward
+    // and be mined; mainnet consensus is unchanged.
+    if (nHeight == 1 && Params().NetworkID() != CBaseChainParams::TESTNET)
+        return 5000000 * COIN;
 
     int halvings = nHeight / 525600; // halving every ~2 years (2-min blocks)
     int64_t nSubsidy = 10 * COIN;