docs: sync OpenAPI - add evm.md

docs/evm.md

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+Verifying your smart contract source code increases transparency and trust in your project. This guide outlines how to verify contracts on Subscan (applicable to Darwinia, Moonbeam, Astar, etc.), specifically focusing on how **Remix users** can modify the generated Metadata JSON to meet Subscan's verification requirements.
+
+### 📍 Example Context
+
+* **Target Network:** Darwinia
+* **Example Contract:** `0x00000000001523057a05d6293c1e5171ee33ee0a`
+* **Tool:** [Remix IDE](https://remix.ethereum.org/)
+
+---
+
+### 🛠 Phase 1: Preparation in Remix
+
+Before verification, ensure your local compilation environment in Remix matches the settings used during the actual deployment **exactly**.
+
+#### 1. Setup Code & Paths
+
+* Open your project in [Remix](https://remix.ethereum.org/).
+* **Attention to Paths:** Ensure your file structure matches the `import` statements.
+* *Example:* Upload or edit `Quacks.sol`.
+
+
+
+#### 2. Configure Compiler
+
+* Navigate to the **Solidity Compiler** tab.
+* **Compiler Version:** Select the exact version used for deployment (e.g., `0.8.x`).
+* **EVM Version:** If a specific version was used (e.g., `paris`, `london`), select it; otherwise, leave as `default`.
+* **Optimization:** Check `Enable optimization` and set the `Runs` value (commonly **200**). **This must match the deployment settings.**
+* Click **Compile Quacks.sol**.
+
+#### 3. Retrieve Metadata JSON
+
+* After successful compilation, go to the **File Explorer** (left sidebar).
+* Look inside the `artifacts/` folder (or root directory depending on Remix version).
+* Locate the file named: `ContractName_metadata.json` (e.g., `Quacks_metadata.json`).
+
+---
+
+### ⚙️ Phase 2: Constructing Standard Input JSON (Crucial Step)
+
+Subscan's "Standard JSON" verification method requires the full source code within the JSON file. However, the default `metadata.json` generated by Remix often contains **URLs (IPFS/Swarm)** instead of the actual source code **content**.
+
+**You must manually edit this JSON file to inject the source code.**
+
+#### 1. Inspect the Generated JSON
+
+Open `Quacks_metadata.json`. In the `sources` section, you might see a structure like this (missing actual code):
+
+```json
+"sources": {
+  "Quacks.sol": {
+    "keccak256": "0x...",
+    "urls": ["bzz-raw://...", "dweb:/ipfs/..."]
+  }
+}
+```
+
+> **Note:** Subscan cannot read these external IPFS/Swarm links — you must replace them with inline `content` (see below).
+
+#### 2. Modify JSON: Inject Source Code
+
+You need to replace or add to the entry with a `"content"` field containing the actual Solidity source string.
+
+**Example of the Modified JSON Structure:**
+
+```json
+{
+  "language": "Solidity",
+  "settings": {
+    "optimizer": {
+      "enabled": true,
+      "runs": 200
+    }
+  },
+  "sources": {
+    "Quacks.sol": {
+      "content": "// SPDX-License-Identifier: MIT\npragma solidity ^0.8.0;\n\ncontract Quacks { ... PASTE FULL SOURCE CODE HERE ... }"
+    },
+    "@openzeppelin/contracts-upgradeable/access/AccessControlUpgradeable.sol": {
+      "content": "// SPDX-License-Identifier: MIT\n// OpenZeppelin Contracts...\n... PASTE FULL LIBRARY SOURCE HERE ..."
+    }
+  }
+}
+```
+
+> **💡 Tips:**
+> * **All** imported files must be listed in `sources`.
+> * The value of `"content"` must be a string (watch out for newlines `\n` and escaping quotes).
+> * If you are using Hardhat/Foundry, their generated `build-info` files already contain the `content` field, so this manual step is not needed.
+>
+>
+
+#### 3. Save the File
+
+Save your modified JSON file locally as `Standard-Input.json`.
+
+---
+
+### 🚀 Phase 3: Verify on Subscan
+
+#### 1. Navigate to Contract Page
+
+* Go to the [Subscan Contract Verify Tool - Darwinia network as an example](https://darwinia.subscan.io/verify_contract).
+* In the Subscan explorer top navigation bar, select **Tools** → **Contract Verification Tool**.
+
+
+#### 2. Upload Configuration
+
+* **Verification Method:** Select `Standard-JSON-Input`.
+* **Compiler Version:** Select the version you used in Remix.
+* **Upload File:** Upload the `Standard-Input.json` you created in Phase 2.
+
+#### 3. Submit
+
+Click **Verify**. If the JSON format is correct and the compiled bytecode matches the on-chain bytecode, the verification will succeed.
+
+#### 4. View and Interact After Verification
+
+After verification succeeds, search the contract address on the target network and open the **Contract** tab to:
+* **View Code** (source + metadata)
+* Use **Read** and **Write** to interact with the contract
+* **Example:** [Contract Detail page - Darwinia network as an example](https://darwinia.subscan.io/account/0x00000000001523057a05d6293c1e5171ee33ee0a?tab=contract)
+
+
+---
+
+### ❓ Troubleshooting
+
+| Issue                  | Possible Cause & Solution                                                                                                                                                        |
+|------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| **Bytecode mismatch**  | **Optimization Runs:** Did you use 200 runs in Remix but default in the JSON? Ensure they match.<br>                                                                             |
+|                        | **EVM Version:** Ensure the EVM version (e.g., London/Paris) is consistent.                                                                                                      |
+| **Parsing Error**      | **JSON Syntax:** Ensure the pasted source code in the JSON doesn't break the JSON string format (escape quotes `"` with `\"`).                                                   |
+| **Alternative Method** | If manual JSON editing is too difficult, install the **"Flattener"** plugin in Remix. Flatten your code into one file, and use the **"Flatten Code"** method on Subscan instead. |
+
+### 📚 References
+
+* [Solidity Compiler Input/Output JSON Description](https://docs.soliditylang.org/en/v0.5.8/using-the-compiler.html#compiler-input-and-output-json-description)