Add checkpoints to 2.2M+, bump orphan limit to 2000, add modernization roadmap

- Add mainnet+testnet checkpoints at blocks 2190000, 2200000, 2205000
- Bump MAX_ORPHAN_BLOCKS from 750 to 2000 (prevents fork deadlocks)
- Add MODERNIZATION_ROADMAP.md with prioritized improvement plan

These changes prevent the exact fork deadlock that happened during
the Apr 17-19 incident: post-IBD orphan limit of 750 was too low,
causing nodes to deadlock when divergent blocks arrived.

MODERNIZATION_ROADMAP.md

@@ -0,0 +1,210 @@
+# Triangles Modernization Roadmap
+
+**Goal:** Make TRI faster to sync, safer for wallets, and more useful as a currency — without breaking consensus.
+
+**Invariant:** Any change that modifies block validation, stake modifier computation, transaction format, or signature verification MUST preserve exact consensus with existing v5.x nodes. When in doubt, test against a synced v5.8.1 node.
+
+---
+
+## Priority 1: Faster Syncing (High Impact, Low Risk)
+
+### 1.1 Update Checkpoints (Easy, Immediate)
+**Problem:** Last hardcoded checkpoint is at block 2,186,940. `IsInitialBlockDownload()` returns false past this point, causing orphan limit to drop from 4000 to 750 — exactly what caused the fork deadlock.
+
+**Fix:** Add checkpoints every ~50,000 blocks up to current height (~2,207,000+).
+```cpp
+// src/checkpoints.cpp - add recent checkpoints
+{2190000, uint256("...")},
+{2195000, uint256("...")},
+{2200000, uint256("...")},
+{2205000, uint256("...")},
+{2210000, uint256("...")},
+```
+**Risk:** None — checkpoints are only used for IBD detection and quick rejection of clearly wrong chains.
+
+### 1.2 Increase Post-Checkpoint Orphan Limit (Easy)
+**Problem:** 750 orphans after IBD is too low for a low-peer network. During the fork incident, 750 orphans filled up and the node deadlocked.
+
+**Fix:**
+```cpp
+// src/main.h
+static const unsigned int MAX_ORPHAN_BLOCKS = 2000;  // was 750
+```
+**Risk:** Slightly more memory usage during forks. Worth it for resilience.
+
+### 1.3 Parallel Block Download (Medium Effort)
+**Problem:** Current implementation downloads blocks sequentially from one peer at a time during IBD.
+
+**Fix:** Increase batch sizes and allow concurrent block downloads from multiple peers:
+```cpp
+// src/main.cpp
+// During IBD, request blocks from multiple peers simultaneously
+unsigned int nGetDataBatchSize = IsInitialBlockDownload() ? 8000 : 1000;  // was 4000
+```
+**Risk:** Low — larger batch sizes are already proven in Bitcoin forks.
+
+### 1.4 Header-First Sync (Medium Effort)
+**Problem:** Node downloads full blocks before validating headers. A bad peer can waste bandwidth.
+
+**Fix:** Download and validate all headers first (compact ~80 bytes each), then download full blocks only for the best chain.
+- Separate `getheaders`/`headers` message handling
+- Download blocks only for the best header chain
+- Reduces wasted bandwidth during forks by 95%+
+
+### 1.5 Bootstrap Over HTTPS with Resume (Easy)
+**Problem:** Built-in bootstrap (`-bootstrap`) uses raw TCP and can't resume interrupted downloads.
+
+**Fix:** The existing `bootstrap.cpp` already supports downloading. Add:
+- Resume support (Range headers)
+- SHA256 verification of downloaded archive
+- Better progress reporting
+- Fallback mirrors
+
+---
+
+## Priority 2: Wallet Safety (Critical)
+
+### 2.1 Automatic Wallet Backup Before Dangerous Operations (Easy)
+**Problem:** Corrupt wallet = lost funds. No automatic backup before risky operations.
+
+**Fix:** In `walletdb.cpp`, before any rewrite:
+```cpp
+// Before wallet.dat rewrite, copy to wallet.dat.bak
+if (boost::filesystem::exists(pathWallet)) {
+    boost::filesystem::copy_file(pathWallet, pathWallet + ".bak",
+        boost::filesystem::copy_option::overwrite_if_exists);
+}
+```
+
+### 2.2 Detect and Report BDB Corruption (Easy)
+**Problem:** BDB corruption silently corrupts wallet. User doesn't know until it's too late.
+
+**Fix:** Add wallet integrity check on load:
+```cpp
+// In CWallet::LoadWallet()
+// After opening, verify BDB environment is healthy
+// If DB_RUNRECOVERY, auto-salvage and warn user
+```
+
+### 2.3 Wallet.dat Versioning (Medium Effort)
+**Problem:** Single wallet.dat file. If it corrupts during write, funds are lost.
+
+**Fix:** Implement copy-on-write wallet saves:
+- Write new wallet data to `wallet.dat.new`
+- Atomically rename `wallet.dat` → `wallet.dat.old`, `wallet.dat.new` → `wallet.dat`
+- Keep last 3 wallet revisions
+- On load, try wallet.dat first, fall back to wallet.dat.old if corrupt
+
+### 2.4 Seed Phrase / HD Wallet (High Effort, High Impact)
+**Problem:** Losing wallet.dat = losing everything. No recovery mechanism.
+
+**Fix:** Implement BIP39/BIP44 HD wallet as optional upgrade:
+- Generate 12/24-word seed phrase on new wallet creation
+- Derive all keys from seed deterministically
+- Import seed on any device to recover wallet
+- Keep backward compatibility with existing non-HD wallets
+
+---
+
+## Priority 3: Network Resilience (Medium Impact)
+
+### 3.1 Better Peer Management (Medium Effort)
+**Problem:** Low peer counts (2-6) lead to fork divergence. No prioritization of reliable peers.
+
+**Fix:**
+- Peer reliability scoring (track which peers provide valid blocks)
+- Prefer peers that are ahead and on the same chain
+- Automatic disconnection of stale/forked peers
+- Increase default `maxconnections` from 64 to 128
+
+### 3.2 Compact Block Relay (High Effort)
+**Problem:** Full blocks are sent even when the receiver likely already has most transactions.
+
+**Fix:** Implement BIP 152 compact blocks:
+- Send block header + short transaction IDs
+- Receiver fills in from mempool, only requests missing transactions
+- Reduces bandwidth by ~90% during normal operation
+
+### 3.3 DNS Seed Infrastructure (Easy)
+**Problem:** `dnsseed=0` when Tor-only means no automatic peer discovery.
+
+**Fix:** Run a DNS seed server that resolves to known reliable onion addresses:
+```
+seed.cryptographic-triangles.org → returns onion addresses of healthy nodes
+```
+
+---
+
+## Priority 4: User Experience (Medium Impact)
+
+### 4.1 Progress Reporting for IBD (Easy)
+**Problem:** Users see "downloading blocks..." with no useful progress indicator.
+
+**Fix:**
+- Report `headers` vs `blocks` progress separately
+- Show estimated time remaining based on download speed
+- Log progress every 1000 blocks (currently every 5000)
+- Qt wallet: update progress bar more frequently
+
+### 4.2 Staking Dashboard Improvements (Easy)
+**Problem:** Qt wallet shows staking info but not clearly.
+
+**Fix:**
+- Show expected time to stake more prominently
+- Display staking weight as percentage of network
+- Notify when stake is found (system notification)
+- Show "staking" indicator in system tray
+
+### 4.3 Transaction Fee Estimation (Medium Effort)
+**Problem:** No fee estimation. Users guess.
+
+**Fix:** Track recent block inclusion rates by fee level, provide fee recommendations.
+
+---
+
+## Priority 5: Code Modernization (Low Urgency, Good Hygiene)
+
+### 5.1 C++17/20 Features
+- Replace raw pointers with smart pointers where safe
+- Use `std::optional`, `std::string_view`, `std::filesystem`
+- Replace boost::filesystem with std::filesystem (C++17)
+
+### 5.2 Build System
+- CMake is already in place (good)
+- Add sanitizers (ASAN, UBSAN) to CI
+- Static analysis with clang-tidy
+
+### 5.3 Testing
+- Current test coverage is thin
+- Add unit tests for:
+  - Checkpoint validation
+  - Stake modifier computation
+  - Bootstrap download/resume
+  - Wallet BDB recovery
+  - Orphan block handling
+
+---
+
+## What NOT to Change
+
+These are consensus-critical and must remain identical:
+- Block validation rules
+- Stake modifier computation (`ComputeNextStakeModifier`)
+- Transaction signature verification
+- Block reward schedule
+- PoW/PoS target computation
+- Chain trust / difficulty adjustment
+- Message serialization format
+- Protocol version handshaking
+
+Any change to these requires a coordinated network upgrade (hard fork).
+
+---
+
+## Implementation Order
+
+1. **This week:** Update checkpoints (1.1), increase orphan limit (1.2), wallet backup before save (2.1)
+2. **Next week:** Better progress reporting (4.1), increase batch size (1.3)
+3. **Month 1:** Wallet versioning (2.3), bootstrap resume (1.5)
+4. **Month 2:** Header-first sync (1.4), peer reliability (3.1)
+5. **Month 3+:** HD wallet (2.4), compact blocks (3.2)

src/checkpoints.cpp

@@ -33,6 +33,9 @@ namespace Checkpoints
         { 10881, uint256("0x4b6554c45e1e6764a6f3c309c47baf53c9edd81f624e52b072518cd15da237e6")},
         { 17650, uint256("0x224940e1f986a202209b8e762728d1452ab45870c308abf84905674acf326a47")},
         {2186940, uint256("0xbd952e8d4a612e336d840ad924a7e09395e36bcd9d929b302e47e60b5c3098c0")},
+        {2190000, uint256("0x682baf783581468ba18f9967254a7f3944e8b8c4cc7101e7d99b68f4f9dd5271")},
+        {2200000, uint256("0x0a8d0442f031f1258120f713f34e45f4f9a625fb753558e27b89b32ad5a9a740")},
+        {2205000, uint256("0xf7aa893ec012181e321783d6a5487addf6997377908faa3e760c9054a4217d29")},
     };
 
     static MapCheckpoints mapCheckpointsTestnet = {
@@ -49,6 +52,9 @@ namespace Checkpoints
         { 10881, uint256("0x4b6554c45e1e6764a6f3c309c47baf53c9edd81f624e52b072518cd15da237e6")},
         { 17650, uint256("0x224940e1f986a202209b8e762728d1452ab45870c308abf84905674acf326a47")},
         {2186940, uint256("0xbd952e8d4a612e336d840ad924a7e09395e36bcd9d929b302e47e60b5c3098c0")},
+        {2190000, uint256("0x682baf783581468ba18f9967254a7f3944e8b8c4cc7101e7d99b68f4f9dd5271")},
+        {2200000, uint256("0x0a8d0442f031f1258120f713f34e45f4f9a625fb753558e27b89b32ad5a9a740")},
+        {2205000, uint256("0xf7aa893ec012181e321783d6a5487addf6997377908faa3e760c9054a4217d29")},
     };
 
     bool CheckHardened(int nHeight, const uint256& hash)

src/main.h

@@ -37,7 +37,7 @@ static const unsigned int MAX_BLOCK_SIZE = 1000000;
 static const unsigned int MAX_BLOCK_SIZE_GEN = MAX_BLOCK_SIZE/2;
 static const unsigned int MAX_BLOCK_SIGOPS = MAX_BLOCK_SIZE/50;
 static const unsigned int MAX_ORPHAN_TRANSACTIONS = MAX_BLOCK_SIZE/100;
-static const unsigned int MAX_ORPHAN_BLOCKS = 750;
+static const unsigned int MAX_ORPHAN_BLOCKS = 2000;
 static const unsigned int MAX_ORPHAN_BLOCKS_IBD = 4000;
 static const unsigned int MAX_INV_SZ = 50000;
 static const int64_t MIN_TX_FEE = (1 * CENT) / 100;