From 89f6d045c8e3dacbfbb369a3ac89c0c33de22b4c Mon Sep 17 00:00:00 2001
From: mtg0001 <106211915+mtg0001@users.noreply.github.com>
Date: Sun, 2 Aug 2026 10:56:50 -0300
Subject: Keep HD change recoverable and bound message stalls (#109)

Change from an HD wallet now goes to a newly derived phrase-backed key instead of reusing a spent input's key. Reusing an input key silently moved value back to a key the phrase cannot reproduce; if derivation fails the transaction is refused rather than creating unrecoverable change. Legacy wallets with no seed keep the 0.1.0 behaviour. Restore also scans past the pre-generated key-pool window before treating an empty batch as the end.

The message parser no longer consumes a header it cannot complete: it reads from a copy, so the O(n) reinsert and the 100 ms sleep inside the shared message thread are gone, and a peer that sits on an incomplete payload is disconnected after two minutes. The wire cap drops from 256 MB to MAX_SIZE. New net-message self-test covers complete, incomplete, stale and oversized headers.

Verified here: clean rebuild, all self-tests pass, lock order checked (no path takes cs_keyPool before cs_mapWallet), and a node built from this branch synced from genesis to the chain tip on the live network with zero rejections.
---
 src/walletcmd.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

(limited to 'src/walletcmd.cpp')

diff --git a/src/walletcmd.cpp b/src/walletcmd.cpp
index 8eb3592..fae2095 100644
--- a/src/walletcmd.cpp
+++ b/src/walletcmd.cpp
@@ -25,6 +25,10 @@
 // would restore a wallet that looks empty.
 static const int RESTORE_BATCH   = 100;
 static const int RESTORE_MAX     = 10000;
+// The wallet may have a full unused key pool in front of a change address
+// created while spending pre-phrase coins. Looking only one empty batch ahead
+// can stop just before that change output.
+static const int RESTORE_MIN_SCAN = KEYPOOL_SIZE + RESTORE_BATCH;
 
 int CmdNewPhrase()
 {
@@ -105,6 +109,7 @@ bool RestoreFromPhrase(const std::string& strMnemonic,
     // up nothing. Every derived key is written to the wallet before the scan,
     // because the scan asks the wallet what belongs to it.
     int nTotalDerived = (int)nHDNext;
+    int nStopDepth = max(nMinDepth, RESTORE_MIN_SCAN);
     while (nTotalDerived < RESTORE_MAX)
     {
         // Count wallet transactions, not scan hits.
@@ -146,7 +151,7 @@ bool RestoreFromPhrase(const std::string& strMnemonic,
 
         // A whole batch with nothing in it means far enough -- unless the
         // caller asked to look deeper anyway.
-        if (nWalletAfter == nWalletBefore && nTotalDerived >= nMinDepth)
+        if (nWalletAfter == nWalletBefore && nTotalDerived >= nStopDepth)
             break;
     }
 
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