Fix PPLNS: use raw chain head, not verified — pay all miners from start

Critical bug: best_share_hash() returned the verified chain's best head.
With slow verification (132/984 shares), PPLNS only saw one miner's shares
and blocks only paid that miner — effectively stealing from other miners.

p2pool uses tracker.items (raw chain) for PPLNS, not tracker.verified.
Verification is for detecting bad shares/peers, not restricting payouts.

Fix: always return the tallest raw chain head for PPLNS computation.
This ensures all miners get their fair share from the first block found,
even if verification hasn't caught up yet.

Author: frstrtr

src/impl/ltc/node.cpp

@@ -508,15 +508,17 @@ void NodeImpl::broadcast_share(const uint256& share_hash)
 
 uint256 NodeImpl::best_share_hash()
 {
-    // Return the cached result from the most recent think() cycle.
-    // Falls back to O(heads) scan only when think() hasn't run yet.
-    if (!m_best_share_hash.IsNull())
-        return m_best_share_hash;
-
+    // p2pool uses the RAW chain (tracker.items) for PPLNS, not the verified
+    // chain. This ensures all miners get paid from the first block, even if
+    // verification hasn't caught up yet. Verification is for detecting bad
+    // shares/peers, not for restricting PPLNS distribution.
+    //
+    // Always return the tallest raw chain head. The verified best (from
+    // think()) is used for peer scoring and ban decisions, not for payouts.
     if (!m_chain || m_chain->size() == 0)
         return uint256::ZERO;
 
-    // Pick the head with the greatest height
+    // Pick the head with the greatest height in the RAW chain
     uint256 best;
     int32_t best_height = -1;
     for (const auto& [head_hash, tail_hash] : m_chain->get_heads())