BIP95: Change proposed Testnet 5 genesis block structure

This moves the anti-pre-mine commitment back into `pszTimestamp` and
keeps it as ASCII text, rather than using it as a fake public key. The
genesis transaction's output is replaced by an `OP_RETURN` to avoid
confusion over spendability. Using the `OP_RETURN` output and `nVersion`
rolling for additional nonce bits are explicitly allowed.

bip-0095.md

@@ -9,7 +9,7 @@
   Assigned: 2026-06-22
   License: CC0-1.0
   Discussion: 2026-06-02: https://groups.google.com/g/bitcoindev/c/kGUMTxOvdJA
-  Version: 0.2.0
+  Version: 0.3.0
   Requires: 54
   Replaces: 94
 ```
@@ -76,30 +76,35 @@ from block 1, as specified above.
 
 ### Genesis Block
 
-TODO: Mine the block. The values below are placeholders inherited from Testnet 4. They are
+TODO: Mine the block. The values below are placeholders. They are
-the genesis block's header fields together with the `Message` and `Pubkey` of its coinbase
+the genesis block's header fields together with the `Message` and
-transaction. Notes for the miner:
+`scriptPubKey` of its coinbase transaction. Notes for the miner:
 
-- `Pubkey` is the public key in the coinbase transaction's pay-to-public-key (P2PK) output. Use a
+- `scriptPubKey` is the script public key in the coinbase transaction's
-  recent Bitcoin mainnet block hash.[^pubkey-methodology]
+  output. It is `OP_RETURN` followed by a push of 8-bytes of extranonce
-- `Message` is an arbitrary string in the coinbase input script, like the newspaper headline in
+  space, as it is unspendable in any event, and this avoids bike shedding
-  Bitcoin's mainnet genesis block. Testnet 4 used it to carry the anti-pre-mine commitment, but
+  over its content.
-  Testnet 5 places that in the `Pubkey` instead, so the `Message` should be left empty, which also
+- `Message` is a string in the coinbase input script, and carries a
-  avoids bike shedding over its content.
+  recent Bitcoin mainnet block hash as an anti-pre-mine commitment,
-- `Time stamp` time of mining or that of the block which hash is used in `Pubkey`
+  serving the same purpose as the newspaper headline in Bitcoin's mainnet
-- `nBits`: `0x1a0fffff`, per the raised minimum difficulty.
+  genesis block.
-- `Version: 1`
+- `Time stamp` is the time of mining or that of the block which hash is
+  used in `Message`
+- `nBits` is `0x1a0fffff`, per the raised minimum difficulty.
+- `Version` is used for version-rolling to meet the difficulty.
 
-Testnet 4 placeholders:
+Placeholders:
 
-> * Message: <code>03/May/2024 000000000000000000001ebd58c244970b3aa9d783bb001011fbe8ea8e98e00e</code>
+> (Note, these values have the wrong nBits value (too low difficulty) and are pre-mined so are not suitable for use)
-> * Pubkey: <code>000000000000000000000000000000000000000000000000000000000000000000</code>
+>
-> * Time stamp: 1714777860
+> * Message: "2026-11-03 974343 00000000000000000000a86d6da2c1563d08668d9ec18cce58cb8c865d4a31c8"
-> * Nonce: 393743547
+> * scriptPubKey: <code>0x6a089763e96a00000000</code>
-> * Difficulty: <code>0x1d00ffff</code>
+> * Time stamp: 1793680278
-> * Version: 1
+> * Nonce: <code>0x73ba1699</code>
-> 
+> * nBits: <code>0x1b07fff8</code>
-> The resulting Genesis block hash is <code>00000000da84f2bafbbc53dee25a72ae507ff4914b867c565be350b0da8bf043</code>, and the block hex is <code>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</code>.
+> * Version: <code>0x201c4000</code>
+>
+> The resulting Genesis block hash is <code>000000000001bd3ade1e24d07c1a3677d4868c34f2f1696fa419e3b9f061b1e0</code>, and the block hex is <code>00401c200000000000000000000000000000000000000000000000000000000000000000de48bbaa869592873fc4e5042f2931f9b42bb7e8ddeccd373df845d80983409b9663e96af8ff071b9916ba730101000000010000000000000000000000000000000000000000000000000000000000000000ffffffff5b04ffff001d01044c52323032362d31312d3033203937343334332030303030303030303030303030303030303030306138366436646132633135363364303836363864396563313863636535386362386338363564346133316338ffffffff0100f2052a010000000a6a089763e96a0000000000000000</code>.
 
 ### Message Start
 
@@ -173,13 +178,10 @@ This document is licensed under the Creative Commons CC0 1.0 Universal license.
 
 ## Changelog
 
+* __0.3.0__ (2026-11-05):
+    * Move commitment back to scriptSig, and use `OP_RETURN` for output.
 * __0.2.0__ (2026-11-05):
     * Change default P2P port from 18335 to 18353
 * __0.1.0__ (2026-06-02):
     * Initial draft
 
-[^pubkey-methodology]: The `Pubkey` field is the public key placed in the coinbase transaction's
-  output as a pay-to-public-key (P2PK) script. Setting it to a recent Bitcoin mainnet block hash
-  serves two purposes: the resulting output is provably unspendable, and the referenced block hash
-  acts as an anti-pre-mine commitment, since the genesis block cannot have been created before that
-  mainnet block existed.