Add DRBalancerVault contract for system DR rebalancing

Implement a vault that holds underlying (AMPL) and perp (SPOT) tokens
and auto-rebalances to maintain the system's target deviation ratio via
IRolloverVault swaps.

Key features:
- Deposit underlying tokens and mint vault notes (LP tokens)
- Redeem notes for proportional underlying + perp tokens
- Auto-rebalance when system DR is outside equilibrium zone:
  - DR < 1 (perpTVL too high): redeem perps to decrease perpTVL
  - DR > 1 (perpTVL too low): mint perps to increase perpTVL
- Rebalance formula: requiredChange = perpTVL × |dr - targetDR|
  (rolloverVaultTVL unchanged during flash mint/redeem)
- Liquidity limits based on swap direction:
  - underlying->perp: limited by underlying balance
  - perp->underlying: limited by perp value held
- Separate lag factors and percentage limits for each direction
- Slippage protection with configurable max swap fee percentage
- Keeper-controlled pause functionality

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: aalavandhan

CLAUDE.md

@@ -0,0 +1,87 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+SPOT Protocol is a monorepo for an inflation-resistant store of value backed by AMPL derivatives. It contains smart contracts and subgraph infrastructure across four workspaces.
+
+## Monorepo Structure
+
+- **spot-contracts** - Core SPOT protocol contracts (PerpetualTranche, BondIssuer, RolloverVault, FeePolicy, RouterV2)
+- **spot-vaults** - Vault strategies (BillBroker for SPOT-USDC trading)
+- **spot-subgraph** - The Graph indexing for SPOT protocol
+- **spot-staking-subgraph** - The Graph indexing for SPOT staking
+
+## Common Commands
+
+### All Workspaces (from root)
+```bash
+yarn install                              # Install dependencies
+yarn workspaces foreach run compile       # Compile all contracts
+yarn workspaces foreach run test          # Run all tests
+yarn workspaces foreach run lint          # Check linting
+yarn workspaces foreach run lint:fix      # Fix lint issues
+yarn workspaces foreach run coverage      # Run coverage
+```
+
+### Single Workspace (from spot-contracts or spot-vaults)
+```bash
+yarn compile                  # Compile contracts
+yarn test                     # Run all tests
+yarn test test/RouterV2.ts    # Run single test file
+yarn coverage                 # Code coverage report
+yarn lint                     # Run all linters
+yarn lint:fix                 # Auto-fix lint issues
+yarn profile                  # Tests with gas reporting (REPORT_GAS=true)
+```
+
+### Subgraph (from spot-subgraph)
+```bash
+yarn codegen                  # Generate GraphQL types
+yarn build                    # Build subgraph
+```
+
+## Technology Stack
+
+- **Solidity**: 0.8.20 (spot-contracts), multiple versions 0.7.6-0.8.24 (spot-vaults)
+- **Framework**: Hardhat v3.1.0 (spot-contracts), Hardhat v2.24.1 (spot-vaults)
+- **Node**: v20+ required
+- **Package Manager**: Yarn 3.2.1 with workspaces
+- **Testing**: Mocha + Chai + Ethers.js v6
+
+## Code Style
+
+- **Solidity**: 4-space indent, Solhint linting
+- **TypeScript**: 2-space indent, ESLint + Prettier
+- **Print width**: 120 characters
+- **Quotes**: Double quotes
+
+## Key Contract Interfaces
+
+Interfaces in `spot-contracts/contracts/_interfaces/` define the protocol API:
+- `IPerpetualTranche.sol` - Core SPOT token interface
+- `IBondIssuer.sol` - Bond issuance interface
+- `IRolloverVault.sol` - Vault operations interface
+- `IFeePolicy.sol` - Fee calculation interface
+
+## Deployment
+
+Deployment tasks are in `/tasks/deploy/` directories. Networks configured: hardhat, ganache, sepolia (testnet), mainnet.
+
+**Mainnet Deployed Contracts:**
+- SPOT: 0xC1f33e0cf7e40a67375007104B929E49a581bafE
+- Router: 0xCe2878d1f2901EFaF48cd456E586B470C145d1BC
+- Bill Broker: 0xA088Aef966CAD7fE0B38e28c2E07590127Ab4ccB
+
+## Environment Variables
+
+Required for deployment/operations (configure in `.env` files):
+- `INFURA_SECRET` / `ALCHEMY_SECRET` - RPC endpoints
+- `PROD_MNEMONIC` - Deployment wallet
+- `ETHERSCAN_API_KEY` - Contract verification
+- `REPORT_GAS` - Enable gas reporter
+
+## Licensing
+
+BUSL-1.1 with GPL-3.0-or-later option for interface files and subgraph code.

spot-contracts/package.json

@@ -26,7 +26,7 @@
     "@ethersproject/providers": "^5.6.8",
     "@nomicfoundation/hardhat-chai-matchers": "latest",
     "@nomicfoundation/hardhat-ethers": "^3.0.0",
-    "@nomicfoundation/hardhat-verify": "latest",
+    "@nomicfoundation/hardhat-verify": "^2.0.0",
     "@nomiclabs/hardhat-waffle": "^2.0.6",
     "@openzeppelin/hardhat-upgrades": "^3.0.4",
     "@openzeppelin/upgrades-core": "latest",