feat: add GM-NET verifiable state anchoring

docs/standalone-usage.md

@@ -0,0 +1,27 @@
+# GM-NET Standalone Bridge Usage
+
+If the official Gitlawb integration is still pending, you can use the bridge contract directly to anchor your repository state.
+
+## Contract Address (Base)
+`0x...` (Deploying soon)
+
+## Usage Example (ethers.js)
+
+```javascript
+const bridge = new ethers.Contract(BRIDGE_ADDRESS, BRIDGE_ABI, signer);
+
+// 1. Prepare your GM-NET state root
+const stateRoot = "0x..."; 
+
+// 2. Anchor your repo state
+const tx = await bridge.anchorRepoState("did:key:z6Mk...", stateRoot);
+await tx.wait();
+
+console.log("State anchored to GM-NET!");
+```
+
+## Verification
+You can verify the latest anchored root for any DID:
+```javascript
+const root = await bridge.latestStateRoot(ethers.utils.id("did:key:z6Mk..."));
+```

src/GitlawbStateAnchor.sol

@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.24;
+
+interface IGitlawbDIDRegistry {
+    function didToOwner(bytes32 didHash) external view returns (address);
+}
+
+/// @title GitlawbStateAnchor
+/// @notice Bridge between Gitlawb DIDs and GM-NET verifiable state roots.
+/// @dev Powered by @bankr
+contract GitlawbStateAnchor {
+    IGitlawbDIDRegistry public immutable registry;
+
+    /// Maps keccak256(did) => latest anchored state root
+    mapping(bytes32 => bytes32) public latestStateRoot;
+
+    event RepoStateAnchored(bytes32 indexed didHash, bytes32 indexed stateRoot, address indexed anchorer);
+
+    error NotDIDOwner(bytes32 didHash, address caller);
+
+    constructor(address _registry) {
+        registry = IGitlawbDIDRegistry(_registry);
+    }
+
+    /// @notice Anchor a new state root for a Gitlawb DID.
+    /// @param did Full DID string (e.g. "did:key:z6Mk...")
+    /// @param stateRoot The bytes32 root from GM-NET
+    function anchorRepoState(string calldata did, bytes32 stateRoot) external {
+        bytes32 didHash = keccak256(bytes(did));
+        address owner = registry.didToOwner(didHash);
+
+        if (owner != msg.sender) revert NotDIDOwner(didHash, msg.sender);
+
+        latestStateRoot[didHash] = stateRoot;
+        emit RepoStateAnchored(didHash, stateRoot, msg.sender);
+    }
+}