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/content/index.js

@@ -1,2 +1,51 @@
-// AutistMask content script
-// TODO: inject window.ethereum provider into page context
+// AutistMask content script — bridges between inpage (window.ethereum)
+// and the background service worker via extension messaging.
+
+// Inject the inpage script into the page's JS context
+const script = document.createElement("script");
+script.src = (typeof browser !== "undefined" ? browser : chrome).runtime.getURL(
+    "src/content/inpage.js",
+);
+script.onload = function () {
+    this.remove();
+};
+(document.head || document.documentElement).appendChild(script);
+
+// Relay requests from the page to the background script
+window.addEventListener("message", (event) => {
+    if (event.source !== window) return;
+    if (event.data?.type !== "AUTISTMASK_REQUEST") return;
+    const { id, method, params } = event.data;
+
+    const runtime =
+        typeof browser !== "undefined" ? browser.runtime : chrome.runtime;
+
+    runtime.sendMessage(
+        { type: "AUTISTMASK_RPC", id, method, params, origin: location.origin },
+        (response) => {
+            if (response) {
+                window.postMessage(
+                    { type: "AUTISTMASK_RESPONSE", id, ...response },
+                    "*",
+                );
+            }
+        },
+    );
+});
+
+// Listen for events pushed from the background (e.g. accountsChanged)
+const runtime =
+    typeof browser !== "undefined" ? browser.runtime : chrome.runtime;
+
+runtime.onMessage.addListener((msg) => {
+    if (msg.type === "AUTISTMASK_EVENT") {
+        window.postMessage(
+            {
+                type: "AUTISTMASK_EVENT",
+                eventName: msg.eventName,
+                data: msg.data,
+            },
+            "*",
+        );
+    }
+});

src/content/inpage.js

@@ -0,0 +1,128 @@
+// AutistMask inpage script — injected into the page's JS context.
+// Creates window.ethereum (EIP-1193 provider).
+
+(function () {
+    if (typeof window.ethereum !== "undefined") return;
+
+    const CHAIN_ID = "0x1"; // Ethereum mainnet
+
+    const listeners = {};
+    let nextId = 1;
+    const pending = {};
+
+    // Listen for responses from the content script
+    window.addEventListener("message", (event) => {
+        if (event.source !== window) return;
+        if (event.data?.type !== "AUTISTMASK_RESPONSE") return;
+        const { id, result, error } = event.data;
+        const p = pending[id];
+        if (!p) return;
+        delete pending[id];
+        if (error) {
+            p.reject(new Error(error.message || "Request failed"));
+        } else {
+            p.resolve(result);
+        }
+    });
+
+    // Listen for events pushed from the extension
+    window.addEventListener("message", (event) => {
+        if (event.source !== window) return;
+        if (event.data?.type !== "AUTISTMASK_EVENT") return;
+        const { eventName, data } = event.data;
+        emit(eventName, data);
+    });
+
+    function emit(eventName, data) {
+        const cbs = listeners[eventName];
+        if (!cbs) return;
+        for (const cb of cbs) {
+            try {
+                cb(data);
+            } catch (e) {
+                // ignore listener errors
+            }
+        }
+    }
+
+    function request(args) {
+        return new Promise((resolve, reject) => {
+            const id = nextId++;
+            pending[id] = { resolve, reject };
+            window.postMessage(
+                { type: "AUTISTMASK_REQUEST", id, ...args },
+                "*",
+            );
+        });
+    }
+
+    const provider = {
+        isAutistMask: true,
+        isMetaMask: true, // compatibility — many dApps check this
+        chainId: CHAIN_ID,
+        networkVersion: "1",
+        selectedAddress: null,
+
+        request(args) {
+            return request({ method: args.method, params: args.params || [] });
+        },
+
+        // Legacy methods (still used by some dApps)
+        enable() {
+            return this.request({ method: "eth_requestAccounts" });
+        },
+
+        send(methodOrPayload, paramsOrCallback) {
+            // Handle both send(method, params) and send({method, params})
+            if (typeof methodOrPayload === "string") {
+                return this.request({
+                    method: methodOrPayload,
+                    params: paramsOrCallback || [],
+                });
+            }
+            return this.request({
+                method: methodOrPayload.method,
+                params: methodOrPayload.params || [],
+            });
+        },
+
+        sendAsync(payload, callback) {
+            this.request({
+                method: payload.method,
+                params: payload.params || [],
+            })
+                .then((result) =>
+                    callback(null, { id: payload.id, jsonrpc: "2.0", result }),
+                )
+                .catch((err) => callback(err));
+        },
+
+        on(event, cb) {
+            if (!listeners[event]) listeners[event] = [];
+            listeners[event].push(cb);
+            return this;
+        },
+
+        removeListener(event, cb) {
+            if (!listeners[event]) return this;
+            listeners[event] = listeners[event].filter((c) => c !== cb);
+            return this;
+        },
+
+        removeAllListeners(event) {
+            if (event) {
+                delete listeners[event];
+            } else {
+                for (const key of Object.keys(listeners)) {
+                    delete listeners[key];
+                }
+            }
+            return this;
+        },
+    };
+
+    window.ethereum = provider;
+
+    // Announce via EIP-6963 (multi-wallet discovery)
+    window.dispatchEvent(new Event("ethereum#initialized"));
+})();