Implement EIP-1193 provider for dApp connectivity

Three-part architecture:
- inpage.js: creates window.ethereum in page context with
  request(), on(), send(), sendAsync(), enable() methods.
  Sets isMetaMask=true for compatibility.
- content/index.js: bridge between page and extension via
  postMessage (page<->content) and runtime.sendMessage
  (content<->background).
- background/index.js: handles RPC routing. Proxies read-only
  methods (eth_call, eth_getBalance, etc.) to configured RPC.
  Handles eth_requestAccounts (auto-connect for now),
  wallet_switchEthereumChain (mainnet only), and returns
  informative errors for unimplemented signing methods.

Manifests updated with web_accessible_resources for inpage.js.
Build updated to bundle inpage.js as a separate output file.

src/background/index.js

@@ -1,2 +1,218 @@
 // AutistMask background service worker
-// TODO: wallet management, message routing, provider implementation
+// Handles EIP-1193 RPC requests from content scripts and proxies
+// non-sensitive calls to the configured Ethereum JSON-RPC endpoint.
+
+const CHAIN_ID = "0x1";
+const DEFAULT_RPC = "https://eth.llamarpc.com";
+
+const storageApi =
+    typeof browser !== "undefined"
+        ? browser.storage.local
+        : chrome.storage.local;
+const runtime =
+    typeof browser !== "undefined" ? browser.runtime : chrome.runtime;
+
+// Connected sites: { origin: [address, ...] }
+const connectedSites = {};
+
+async function getState() {
+    const result = await storageApi.get("autistmask");
+    return result.autistmask || { wallets: [], rpcUrl: DEFAULT_RPC };
+}
+
+async function getAccounts() {
+    const state = await getState();
+    const accounts = [];
+    for (const wallet of state.wallets) {
+        for (const addr of wallet.addresses) {
+            accounts.push(addr.address);
+        }
+    }
+    return accounts;
+}
+
+async function getRpcUrl() {
+    const state = await getState();
+    return state.rpcUrl || DEFAULT_RPC;
+}
+
+// Proxy an RPC call to the Ethereum node
+async function proxyRpc(method, params) {
+    const rpcUrl = await getRpcUrl();
+    const resp = await fetch(rpcUrl, {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({
+            jsonrpc: "2.0",
+            id: 1,
+            method,
+            params,
+        }),
+    });
+    const json = await resp.json();
+    if (json.error) {
+        throw new Error(json.error.message || "RPC error");
+    }
+    return json.result;
+}
+
+// Methods that are safe to proxy directly to the RPC node
+const PROXY_METHODS = [
+    "eth_blockNumber",
+    "eth_call",
+    "eth_chainId",
+    "eth_estimateGas",
+    "eth_gasPrice",
+    "eth_getBalance",
+    "eth_getBlockByHash",
+    "eth_getBlockByNumber",
+    "eth_getCode",
+    "eth_getLogs",
+    "eth_getStorageAt",
+    "eth_getTransactionByHash",
+    "eth_getTransactionCount",
+    "eth_getTransactionReceipt",
+    "eth_maxPriorityFeePerGas",
+    "eth_sendRawTransaction",
+    "net_version",
+    "web3_clientVersion",
+    "eth_feeHistory",
+    "eth_getBlockTransactionCountByHash",
+    "eth_getBlockTransactionCountByNumber",
+];
+
+async function handleRpc(method, params, origin) {
+    // Methods that need wallet involvement
+    if (method === "eth_requestAccounts" || method === "eth_accounts") {
+        const accounts = await getAccounts();
+        if (accounts.length === 0) {
+            return { error: { message: "No accounts available" } };
+        }
+        // Auto-connect for now (approval flow is a future TODO)
+        connectedSites[origin] = accounts;
+        return { result: accounts };
+    }
+
+    if (method === "eth_chainId") {
+        return { result: CHAIN_ID };
+    }
+
+    if (method === "net_version") {
+        return { result: "1" };
+    }
+
+    if (method === "wallet_switchEthereumChain") {
+        const chainId = params?.[0]?.chainId;
+        if (chainId === CHAIN_ID) {
+            return { result: null };
+        }
+        return {
+            error: {
+                code: 4902,
+                message: "AutistMask only supports Ethereum mainnet.",
+            },
+        };
+    }
+
+    if (method === "wallet_addEthereumChain") {
+        return {
+            error: {
+                code: 4902,
+                message: "AutistMask only supports Ethereum mainnet.",
+            },
+        };
+    }
+
+    if (method === "wallet_requestPermissions") {
+        const accounts = await getAccounts();
+        if (accounts.length === 0) {
+            return { error: { message: "No accounts available" } };
+        }
+        connectedSites[origin] = accounts;
+        return {
+            result: [
+                {
+                    parentCapability: "eth_accounts",
+                    caveats: [
+                        {
+                            type: "restrictReturnedAccounts",
+                            value: accounts,
+                        },
+                    ],
+                },
+            ],
+        };
+    }
+
+    if (method === "wallet_getPermissions") {
+        const accounts = connectedSites[origin] || [];
+        if (accounts.length === 0) {
+            return { result: [] };
+        }
+        return {
+            result: [
+                {
+                    parentCapability: "eth_accounts",
+                    caveats: [
+                        {
+                            type: "restrictReturnedAccounts",
+                            value: accounts,
+                        },
+                    ],
+                },
+            ],
+        };
+    }
+
+    if (method === "personal_sign" || method === "eth_sign") {
+        // TODO: implement signature approval flow
+        return {
+            error: { message: "Signing not yet implemented in AutistMask." },
+        };
+    }
+
+    if (method === "eth_signTypedData_v4" || method === "eth_signTypedData") {
+        // TODO: implement typed data signing
+        return {
+            error: {
+                message:
+                    "Typed data signing not yet implemented in AutistMask.",
+            },
+        };
+    }
+
+    if (method === "eth_sendTransaction") {
+        // TODO: implement transaction signing approval flow
+        // For now, return an error directing the user to use the popup
+        return {
+            error: {
+                message:
+                    "Transaction signing via dApps not yet implemented. Use the AutistMask popup to send transactions.",
+            },
+        };
+    }
+
+    // Proxy safe read-only methods to the RPC node
+    if (PROXY_METHODS.includes(method)) {
+        try {
+            const result = await proxyRpc(method, params);
+            return { result };
+        } catch (e) {
+            return { error: { message: e.message } };
+        }
+    }
+
+    return { error: { message: "Unsupported method: " + method } };
+}
+
+// Listen for messages from content scripts
+runtime.onMessage.addListener((msg, sender, sendResponse) => {
+    if (msg.type !== "AUTISTMASK_RPC") return;
+
+    handleRpc(msg.method, msg.params, msg.origin).then((response) => {
+        sendResponse(response);
+    });
+
+    // Return true to indicate async response
+    return true;
+});