fix: answer the page when a background handler throws (closes #280)

handleRpc(...).then(sendResponse) had no .catch(), and sendResponse is the only
thing that settles the dApp's window.ethereum.request() promise. Any throw
inside handleRpc therefore sent nothing back: the content script posted nothing,
and the page's promise stayed pending forever with no error and no timeout,
indistinguishable from a slow wallet. handleRpc does real work -- state loads,
provider calls, transaction population, approval plumbing -- so "it does not
throw today" was not a property anyone was maintaining.

A rejected handleRpc now answers { code: -32603, message }. -32603 is the
JSON-RPC internal error EIP-1474 defines and EIP-1193 defers to for RPC-layer
failures; no EIP-1193 4xxx code describes "the wallet broke" and none was
invented for it. The cause is not put in the message: the page gets a stable
sentence, the background console gets the method and the throw, so the failure
is visible rather than swallowed.

The two async IIFEs behind AUTISTMASK_TX_RESPONSE and AUTISTMASK_SIGN_RESPONSE
are the same shape one level down. Every statement is inside a try, but a throw
from one of the catch blocks escapes as an unhandled rejection and neither the
popup nor the page is answered. Each gets a last-resort .catch() that settles
the approval through settleApproval() -- the existing chokepoint, with no new
delete or resolve -- and answers the popup. The transaction one reports the
broadcast stage, because it cannot tell whether the transaction reached the
network and that is the wording that does not invite a second send. Every other
message handler on the path is synchronous and cannot leave a promise pending.

Each of the three is driven by a real failure rather than a hook in the handler:
a rejecting extension-storage read, which getState() awaits unguarded, and a
failure classifier that throws while classifying a genuine verification failure.
All three were demonstrated failing against the unfixed code, the RPC one with
sendResponse at zero calls, which is precisely the page-side hang.

TODO.md

@@ -45,6 +45,39 @@ undefined identifiers, which is how
 
 # Completed Steps
 
+- 2026-08-14: A background message handler that throws now rejects the page
+  instead of hanging it. `handleRpc(...).then(sendResponse)` had no `.catch()`,
+  and `sendResponse` is the only thing that settles the dApp's
+  `window.ethereum.request()` promise — so any throw inside `handleRpc` left
+  that promise pending forever, with no error and no timeout, indistinguishable
+  from a slow wallet. It now answers `{ code: -32603, message }` (the JSON-RPC
+  internal error EIP-1474 defines and EIP-1193 defers to; no EIP-1193 4xxx code
+  describes "the wallet broke" and none was invented) and logs the method and
+  the throw to the background console rather than swallowing them. The two async
+  IIFEs behind `AUTISTMASK_TX_RESPONSE` and `AUTISTMASK_SIGN_RESPONSE` were the
+  same shape one level down — every statement inside a `try`, but a throw out of
+  a `catch` block escaping unhandled — and each got a last-resort `.catch()`
+  settling the approval through `settleApproval()` and answering the popup; the
+  transaction one reports the broadcast stage, because it cannot tell whether
+  the transaction reached the network. Every other handler on the path is
+  synchronous. All three are driven by real failures — a rejecting storage read,
+  and a failure classifier that throws while classifying a genuine verification
+  failure — and were demonstrated failing first, the RPC one with `sendResponse`
+  at zero calls ([#280](https://git.eeqj.de/sneak/AutistMask/issues/280)).
+- 2026-08-12: EIP-1193 error codes now reach the page. `src/content/inpage.js`
+  rebuilt every failure as `new Error(error.message)`, so the code the
+  background produced and the content script relayed intact was dropped in the
+  last hop and a dApp checking `err.code === 4001` saw `undefined` — a wallet
+  the user deliberately declined was indistinguishable from one that broke. The
+  provider now rejects with a `ProviderRpcError` carrying `code` and, where the
+  boundary sent one, `data`, passed through verbatim rather than matched against
+  a list, so 4001, 4100 and 4902 all arrive and a future code needs no edit
+  here. An error the background sent with no code stays a plain `Error` with no
+  `code` property, and `message` is unchanged in every case. All four request
+  entry points (`request`, `enable`, `send`, `sendAsync`) are covered by
+  `tests/inpageErrors.test.js`, and the e2e probe that printed the missing code
+  now requires it on the page's Error as well as on the wire, for all four
+  rejected flows ([#274](https://git.eeqj.de/sneak/AutistMask/issues/274)).
 - 2026-08-12: `KNOWN_SYMBOLS` now maps a symbol to the set of contract addresses
   that bear it, not to one of them. A ticker is not unique: seven of the 512
   bundled tokens — `FRAX`, `REUSD`, `TON`, `EURE`, `MSUSD`, `MUSD` and `JPYC` —

src/background/index.js

@@ -57,6 +57,16 @@ const connectedSites = {};
 // Pending approval requests: { id: { origin, hostname, resolve } }
 const pendingApprovals = {};
 
+// What the page is told when a request failed in a way the wallet has no
+// specific answer for. -32603 is the JSON-RPC internal error EIP-1474 defines
+// and EIP-1193 defers to for RPC-layer failures; no EIP-1193 4xxx code
+// describes "the wallet broke", and one is not invented here. The cause is
+// logged rather than put in the message: the page gets a stable sentence, the
+// background console gets the throw.
+const INTERNAL_ERROR_CODE = -32603;
+const INTERNAL_ERROR_MESSAGE =
+    "AutistMask could not complete this request because of an internal error.";
+
 async function getState() {
     const result = await storageApi.get("autistmask");
     return (
@@ -865,8 +875,25 @@ runtime.onMessage.addListener((msg, sender, sendResponse) => {
                 // keep fallback
             }
         }
-        handleRpc(msg.method, msg.params, trustedOrigin).then((response) => {
+        handleRpc(msg.method, msg.params, trustedOrigin)
+            .then((response) => {
                 sendResponse(response);
+            })
+            .catch((err) => {
+                // Without this the page's window.ethereum.request() promise
+                // stays pending forever: no response is sent, the content
+                // script posts nothing back, and the dApp cannot tell the
+                // failure from a slow wallet. handleRpc does real work —
+                // state loads, provider calls, transaction population — so
+                // "it does not throw today" is not a property anyone is
+                // maintaining.
+                log.errorf("RPC request failed:", msg.method, err);
+                sendResponse({
+                    error: {
+                        code: INTERNAL_ERROR_CODE,
+                        message: INTERNAL_ERROR_MESSAGE,
+                    },
+                });
             });
         return true;
     }
@@ -1051,7 +1078,31 @@ runtime.onMessage.addListener((msg, sender, sendResponse) => {
                     stage: TX_STAGE_BROADCAST,
                 });
             }
-        })();
+        })().catch((e) => {
+            // Every statement above is inside a try, but a throw from one of
+            // the catch blocks escapes as an unhandled rejection and neither
+            // the popup nor the page is ever answered. Settle both, through
+            // the same chokepoint as every other retirement. The stage is
+            // broadcast because this cannot tell whether the transaction
+            // reached the network, and that is the wording that does not
+            // invite a second send.
+            log.errorf("transaction approval response failed:", e);
+            settleApproval(
+                msg.id,
+                {
+                    error: {
+                        code: INTERNAL_ERROR_CODE,
+                        message: INTERNAL_ERROR_MESSAGE,
+                    },
+                },
+                { holdsClaim: true },
+            );
+            sendResponse({
+                error: INTERNAL_ERROR_MESSAGE,
+                retryable: false,
+                stage: TX_STAGE_BROADCAST,
+            });
+        });
         return true;
     }
 
@@ -1135,7 +1186,25 @@ runtime.onMessage.addListener((msg, sender, sendResponse) => {
                 }
                 sendResponse({ error: errMsg, retryable });
             }
-        })();
+        })().catch((e) => {
+            // Same shape as the transaction path: a throw out of the catch
+            // block above would leave the popup and the page both waiting.
+            log.errorf("sign approval response failed:", e);
+            settleApproval(
+                msg.id,
+                {
+                    error: {
+                        code: INTERNAL_ERROR_CODE,
+                        message: INTERNAL_ERROR_MESSAGE,
+                    },
+                },
+                { holdsClaim: true },
+            );
+            sendResponse({
+                error: INTERNAL_ERROR_MESSAGE,
+                retryable: false,
+            });
+        });
         return true;
     }
 

src/content/inpage.js

@@ -11,6 +11,39 @@
     let nextId = 1;
     const pending = {};
 
+    // EIP-1193 ProviderRpcError: `code`, `message`, optional `data`. A class
+    // rather than properties bolted onto an Error because this object crosses
+    // no boundary after construction — it is built in the page's own realm and
+    // handed straight to the caller's catch — so the prototype survives and
+    // `error.name` is a stable thing for a dApp to see.
+    class ProviderRpcError extends Error {
+        constructor(code, message, data) {
+            super(message);
+            this.name = "ProviderRpcError";
+            this.code = code;
+            if (data !== undefined) this.data = data;
+        }
+    }
+
+    // Rebuild a boundary error as the error the page catches, carrying the
+    // code (and data) the extension reported. Without this a dApp cannot tell
+    // a user's refusal (4001) from a wallet that broke, and retries or shows
+    // an error instead of accepting the refusal.
+    //
+    // Whatever code arrived is passed through verbatim rather than being
+    // matched against a list: the extension emits 4001, 4100 and 4902 today,
+    // and a code this file has never heard of is still the truth about what
+    // happened. An error reported with no code at all stays a plain Error —
+    // a ProviderRpcError whose `code` is undefined would advertise a
+    // conformance it does not have. `message` is untouched in every case.
+    function toPageError(error) {
+        const message = (error && error.message) || "Request failed";
+        if (error && error.code !== undefined && error.code !== null) {
+            return new ProviderRpcError(error.code, message, error.data);
+        }
+        return new Error(message);
+    }
+
     // Listen for responses from the content script
     window.addEventListener("message", function onUuid(event) {
         if (event.source !== window) return;
@@ -20,7 +53,7 @@
         if (!p) return;
         delete pending[id];
         if (error) {
-            p.reject(new Error(error.message || "Request failed"));
+            p.reject(toPageError(error));
         } else {
             p.resolve(result);
         }

tests/backgroundApproval.test.js

@@ -133,6 +133,14 @@ function loadBackground(options) {
         ensureRecurringAlarms: jest.fn(async () => {}),
         registerAlarmHandlers: jest.fn(),
     }));
+    // The real verification module, except where a test replaces one export
+    // with a throw to drive the handler's own error handling into failing.
+    if (opts.approvalVerify) {
+        jest.doMock("../src/shared/approvalVerify", () => ({
+            ...jest.requireActual("../src/shared/approvalVerify"),
+            ...opts.approvalVerify,
+        }));
+    }
 
     const persisted = {
         wallets: [
@@ -152,7 +160,10 @@ function loadBackground(options) {
     global.chrome = {
         storage: {
             local: {
-                get: jest.fn(async () => ({ autistmask: persisted })),
+                get: jest.fn(
+                    opts.storageGet ||
+                        (async () => ({ autistmask: persisted })),
+                ),
                 set: jest.fn(async () => {}),
             },
         },
@@ -280,6 +291,25 @@ async function settle() {
     for (let i = 0; i < 50; i++) await Promise.resolve();
 }
 
+// Node aborts the worker process on an unhandled rejection; an extension
+// service worker does not — the promise is simply never settled, nothing is
+// sent back, and the page's window.ethereum.request() waits forever. Recording
+// them instead of dying on them keeps that difference visible: the assertion
+// that the page WAS answered is what reports the failure, and the recording is
+// asserted empty alongside it.
+const unhandledRejections = [];
+process.on("unhandledRejection", (reason) => {
+    unhandledRejections.push(reason);
+});
+
+// Node reports an unhandled rejection on the macrotask turn after the promise
+// was left unhandled, which is past everything settle() waits for.
+async function settleIncludingRejections() {
+    await settle();
+    await new Promise((resolve) => setImmediate(resolve));
+    await new Promise((resolve) => setImmediate(resolve));
+}
+
 afterEach(() => {
     delete global.chrome;
     jest.resetModules();
@@ -1034,6 +1064,147 @@ describe("a claimed approval outlives every other retirement path", () => {
     });
 });
 
+// A handler that throws must still answer. `sendResponse` is the only thing
+// that settles the page's window.ethereum.request() promise, so a throw that
+// escapes a handler leaves that promise pending forever — no error, no
+// timeout, indistinguishable from a slow wallet. Each case below drives a real
+// throw out of a handler rather than asserting the catch block exists.
+describe("a handler that throws still settles the page", () => {
+    const INTERNAL_ERROR = {
+        code: -32603,
+        message:
+            "AutistMask could not complete this request because of an internal error.",
+    };
+
+    let errorLog;
+    beforeEach(() => {
+        errorLog = jest.spyOn(console, "error").mockImplementation(() => {});
+        unhandledRejections.length = 0;
+    });
+    afterEach(() => {
+        errorLog.mockRestore();
+    });
+
+    // getState() awaits extension storage unguarded, and every read path in
+    // handleRpc goes through it. A storage read that rejects is the whole
+    // failure — no hook in the handler itself.
+    test("a rejected handleRpc rejects the page instead of hanging it", async () => {
+        const bg = loadBackground({
+            storageGet: async () => {
+                throw new Error("storage unavailable");
+            },
+        });
+
+        const answer = bg.send(
+            { type: "AUTISTMASK_RPC", method: "eth_accounts", params: [] },
+            { origin: ORIGIN },
+        );
+        await settleIncludingRejections();
+
+        // The channel is held open for the async answer, and the answer
+        // arrives.
+        expect(answer.kept).toBe(true);
+        expect(answer.sendResponse).toHaveBeenCalledWith({
+            error: INTERNAL_ERROR,
+        });
+        expect(unhandledRejections).toEqual([]);
+        // Not swallowed: the throw is on the background console, which is how
+        // this class gets caught in future.
+        expect(errorLog).toHaveBeenCalledWith(
+            "[AutistMask]",
+            "RPC request failed:",
+            "eth_accounts",
+            expect.objectContaining({ message: "storage unavailable" }),
+        );
+    });
+
+    // The transaction response handler wraps every statement in a try, so what
+    // escapes it is a throw from inside one of its catch blocks. Here the
+    // failure classifier itself throws while classifying a real verification
+    // failure — the approval is left claimed, so nothing else can settle it.
+    test("a throw while handling a failed transaction settles both the page and the popup", async () => {
+        const bg = loadBackground({
+            approvalVerify: {
+                describeTxFailure: () => {
+                    throw new Error("classifier broke");
+                },
+            },
+        });
+        const pending = bg.requestTx();
+        await settle();
+        const id = pending.id();
+
+        // A real verification failure: the artifact is signed at a nonce the
+        // approval never displayed.
+        const answer = bg.send(
+            {
+                type: "AUTISTMASK_TX_RESPONSE",
+                id,
+                approved: true,
+                rawSignedTx: await signedAtNonce(NONCE + 1),
+            },
+            { url: bg.fromPopup.url },
+        );
+        await settleIncludingRejections();
+
+        expect(bg.broadcastTransaction).not.toHaveBeenCalled();
+        expect(pending.result()).toEqual({ error: INTERNAL_ERROR });
+        expect(answer.sendResponse).toHaveBeenCalledWith({
+            error: INTERNAL_ERROR.message,
+            retryable: false,
+            // The handler cannot tell whether the transaction reached the
+            // network, so the popup must not say "start again from the site".
+            stage: "broadcast",
+        });
+        expect(unhandledRejections).toEqual([]);
+        expect(errorLog).toHaveBeenCalledWith(
+            "[AutistMask]",
+            "transaction approval response failed:",
+            expect.objectContaining({ message: "classifier broke" }),
+        );
+    });
+
+    test("a throw while handling a failed signature settles both the page and the popup", async () => {
+        const bg = loadBackground({
+            approvalVerify: {
+                failureIsRetryable: () => {
+                    throw new Error("classifier broke");
+                },
+            },
+        });
+        const pending = bg.requestSign();
+        await settle();
+
+        // A real verification failure: the active address moved after the
+        // approval was raised.
+        bg.setActiveAddress(other.address);
+        const answer = bg.send(
+            {
+                type: "AUTISTMASK_SIGN_RESPONSE",
+                id: pending.id(),
+                approved: true,
+                signature: await signer.signMessage(
+                    Buffer.from(MESSAGE.slice(2), "hex"),
+                ),
+            },
+            { url: bg.fromPopup.url },
+        );
+        await settleIncludingRejections();
+
+        expect(pending.result()).toEqual({ error: INTERNAL_ERROR });
+        expect(answer.sendResponse).toHaveBeenCalledWith({
+            error: INTERNAL_ERROR.message,
+            retryable: false,
+        });
+        expect(unhandledRejections).toEqual([]);
+        expect(errorLog).toHaveBeenCalledWith(
+            "[AutistMask]",
+            "sign approval response failed:",
+            expect.objectContaining({ message: "classifier broke" }),
+        );
+    });
+});
+
 describe("popup-only messages", () => {
     test("a page sender cannot answer an approval", async () => {
         const bg = loadBackground();

tests/e2e/network.js

@@ -86,9 +86,11 @@ const DAPP_URL = DAPP_ORIGIN + "/";
 // never drive the popup that has to settle it; start() files the promise
 // under a key and settle() collects it once the prompt has been dealt with.
 //
-// The rejection branch records `code` as it arrives. EIP-1193 says a user
-// rejection is a ProviderRpcError carrying code 4001; what the page can
-// actually see is recorded here rather than assumed, and asserted in run.js.
+// The rejection branch records the whole observable shape of the error as it
+// arrives — name, message, and whether a `code` is present at all as distinct
+// from its value. EIP-1193 says a user rejection is a ProviderRpcError
+// carrying code 4001; what the page can actually see is recorded here rather
+// than assumed, and asserted in run.js.
 //
 // The message log is the page's half of the boundary observation: every
 // AUTISTMASK_* message that crosses between this page and the content
@@ -120,6 +122,7 @@ const DAPP_HTML = [
     "                    return {",
     "                        settled: 'rejected',",
     "                        message: String((error && error.message) || error),",
+    "                        name: error ? error.name : undefined,",
     "                        hasCode: !!error && 'code' in Object(error),",
     "                        code: error ? error.code : undefined,",
     "                    };",

tests/e2e/run.js

@@ -1591,15 +1591,14 @@ async function lastResponseError(page) {
 }
 
 // A rejected prompt, asserted at both ends: the page's promise rejected
-// rather than hanging or resolving, and the response that crossed the
-// boundary carried EIP-1193 code 4001.
+// rather than hanging or resolving, and EIP-1193 code 4001 is present both
+// on the wire and on the Error the calling page catches.
 //
-// The code is asserted on the wire because that is the only place it
-// survives. src/content/inpage.js rebuilds the rejection as `new
-// Error(error.message)`, so the Error the calling page catches carries the
-// message and no code. That is reported rather than asserted either way —
-// locking in the current behaviour would make the gap permanent, and
-// asserting the code on the Error would fail today.
+// Both ends matter because they used to disagree. The code crossed the
+// boundary correctly and src/content/inpage.js then threw it away, rebuilding
+// every rejection as `new Error(error.message)` — so a dApp branching on
+// `err.code === 4001` saw undefined and could not tell a refusal from a
+// failure (#274). Asserting only the wire would leave that gap invisible.
 async function assertUserRejection(page, key, label) {
     const outcome = await settleRequest(page, key);
     assert(
@@ -1621,15 +1620,32 @@ async function assertUserRejection(page, key, label) {
             " did not carry EIP-1193 code 4001 across the boundary: " +
             JSON.stringify(error),
     );
+    assert(
+        outcome.hasCode,
+        label +
+            " reached the page as an error with no code property at all, so a " +
+            "dApp cannot tell the user's refusal from a failure: " +
+            JSON.stringify(outcome),
+    );
+    assert(
+        outcome.code === 4001,
+        label +
+            " reached the page with code " +
+            JSON.stringify(outcome.code) +
+            " rather than EIP-1193 4001",
+    );
+    assert(
+        outcome.name === "ProviderRpcError",
+        label +
+            " reached the page as " +
+            JSON.stringify(outcome.name) +
+            " rather than an EIP-1193 ProviderRpcError",
+    );
     console.log(
         "# " +
             label +
-            ": boundary code=" +
-            error.code +
-            " page Error.code=" +
-            JSON.stringify(outcome.code) +
-            " page Error carries a code=" +
-            outcome.hasCode,
+            ": code 4001 on the wire and on the page's " +
+            outcome.name,
     );
     return outcome;
 }

tests/inpageErrors.test.js

@@ -0,0 +1,310 @@
+// The EIP-1193 error the page actually catches (src/content/inpage.js).
+//
+// The bug this pins down (issue #274): the provider rebuilt every failure as
+// `new Error(error.message)`, so the `code` the background produced and the
+// content script relayed intact was thrown away in the last hop. A dApp
+// checking `err.code === 4001` — the standard way to tell "the user said no"
+// from "the wallet broke" — saw undefined, and well-behaved sites showed an
+// error or retried instead of accepting the refusal.
+//
+// inpage.js is a bare IIFE injected into the page's JS context, not a module:
+// it takes no import and exports nothing, and reaches for `window` at load.
+// So it is evaluated here the way the browser evaluates it, against a stub
+// window, and the provider is collected from `window.ethereum`. The globals it
+// touches are passed in as function parameters rather than assigned to
+// globalThis: nothing leaks between tests, and the source is compiled in this
+// realm, so the errors it constructs are comparable against this file's own
+// `Error` — which a second realm's intrinsics would silently defeat.
+//
+// There is no jsdom in this repo; see tests/txStatus.test.js.
+
+const fs = require("fs");
+const path = require("path");
+const { webcrypto } = require("crypto");
+
+const SOURCE = fs.readFileSync(
+    path.join(__dirname, "..", "src", "content", "inpage.js"),
+    "utf8",
+);
+
+const loadInto = new Function(
+    "window",
+    "self",
+    "crypto",
+    "Event",
+    "CustomEvent",
+    SOURCE,
+);
+
+class StubEvent {
+    constructor(type) {
+        this.type = type;
+    }
+}
+
+class StubCustomEvent extends StubEvent {
+    constructor(type, init) {
+        super(type);
+        this.detail = init && init.detail;
+    }
+}
+
+// Every code the background emits on the RPC path today, read out of
+// src/background/index.js. The provider must not know this list — it passes
+// through whatever arrived — but the cases below are the real ones.
+const REJECTED = 4001; // user rejected the request
+const UNAUTHORIZED = 4100; // site not connected / wrong address
+const UNRECOGNIZED_CHAIN = 4902; // switch/add to an unsupported chain
+
+// A stub window with the four things inpage.js touches: message listeners,
+// postMessage out to the content script, window.ethereum, and dispatchEvent
+// for the EIP-6963 announcement.
+function loadProvider() {
+    const messageListeners = [];
+    const posted = [];
+
+    const win = {
+        addEventListener(type, fn) {
+            if (type === "message") messageListeners.push(fn);
+        },
+        removeEventListener(type, fn) {
+            const i = messageListeners.indexOf(fn);
+            if (type === "message" && i !== -1) messageListeners.splice(i, 1);
+        },
+        postMessage(data) {
+            posted.push(data);
+        },
+        dispatchEvent() {
+            return true;
+        },
+    };
+    win.window = win;
+
+    loadInto(win, win, webcrypto, StubEvent, StubCustomEvent);
+
+    // Deliver the content script's answer to an outstanding request. The id is
+    // read back off the wire rather than assumed: inpage.js issues its own
+    // eth_chainId at load, so the first id a test sees is not 1.
+    function respond(response) {
+        const request = posted
+            .filter((m) => m.type === "AUTISTMASK_REQUEST")
+            .pop();
+        expect(request).toBeDefined();
+        const event = {
+            source: win,
+            data: { type: "AUTISTMASK_RESPONSE", id: request.id, ...response },
+        };
+        for (const fn of messageListeners.slice()) fn(event);
+    }
+
+    return { provider: win.ethereum, posted, respond };
+}
+
+// Start a request, answer it with `response`, and hand back the rejection.
+// Fails the test if the call resolves instead.
+async function rejectionFrom(start, response) {
+    const { provider, respond } = loadProvider();
+    const settled = start(provider).then(
+        (result) => ({ resolved: result }),
+        (error) => ({ error }),
+    );
+    // The provider posts synchronously, so the request is already on the wire.
+    respond(response);
+    const outcome = await settled;
+    expect(outcome).not.toHaveProperty("resolved");
+    return outcome.error;
+}
+
+describe("an EIP-1193 code reaches the page", () => {
+    test("a user rejection arrives as code 4001", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "eth_requestAccounts" }),
+            {
+                error: {
+                    code: REJECTED,
+                    message: "User rejected the request.",
+                },
+            },
+        );
+        expect(err.code).toBe(REJECTED);
+        expect(err.message).toBe("User rejected the request.");
+    });
+
+    test("it is a ProviderRpcError, and an Error", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "eth_requestAccounts" }),
+            {
+                error: {
+                    code: REJECTED,
+                    message: "User rejected the request.",
+                },
+            },
+        );
+        expect(err).toBeInstanceOf(Error);
+        expect(err.name).toBe("ProviderRpcError");
+    });
+
+    test("4100 unauthorized arrives intact", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "personal_sign", params: ["0x00"] }),
+            { error: { code: UNAUTHORIZED, message: "Unauthorized" } },
+        );
+        expect(err.code).toBe(UNAUTHORIZED);
+        expect(err.message).toBe("Unauthorized");
+    });
+
+    test("4902 unrecognized chain arrives intact", async () => {
+        const message =
+            "AutistMask supports Ethereum Mainnet and Sepolia Testnet only.";
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "wallet_switchEthereumChain" }),
+            { error: { code: UNRECOGNIZED_CHAIN, message } },
+        );
+        expect(err.code).toBe(UNRECOGNIZED_CHAIN);
+        expect(err.message).toBe(message);
+    });
+
+    // The provider is not allowed to know the list above: a code added to the
+    // background later must reach the page without this file being edited.
+    test("a code the provider has never heard of is passed through", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "eth_accounts" }),
+            { error: { code: 4900, message: "Disconnected" } },
+        );
+        expect(err.code).toBe(4900);
+    });
+
+    test("data is carried when the boundary sent it", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "eth_call" }),
+            {
+                error: {
+                    code: -32000,
+                    message: "execution reverted",
+                    data: "0x08c379a0",
+                },
+            },
+        );
+        expect(err.code).toBe(-32000);
+        expect(err.data).toBe("0x08c379a0");
+    });
+
+    test("no data property is invented when the boundary sent none", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "eth_requestAccounts" }),
+            {
+                error: {
+                    code: REJECTED,
+                    message: "User rejected the request.",
+                },
+            },
+        );
+        expect("data" in err).toBe(false);
+    });
+});
+
+describe("the message is untouched", () => {
+    test("a coded error keeps the message byte for byte", async () => {
+        const message =
+            "This site asked to sign as an address that is not " +
+            "the active one.";
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "personal_sign" }),
+            { error: { code: UNAUTHORIZED, message } },
+        );
+        expect(err.message).toBe(message);
+    });
+
+    test("an error the background sent with no code keeps its message", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "eth_sendTransaction" }),
+            { error: { message: "No accounts available" } },
+        );
+        expect(err.message).toBe("No accounts available");
+    });
+
+    // A ProviderRpcError whose code is undefined would claim a conformance it
+    // does not have, and `'code' in err` is exactly what a careful dApp asks.
+    test("an error with no code gets no code property at all", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "eth_sendTransaction" }),
+            { error: { message: "No accounts available" } },
+        );
+        expect(err).toBeInstanceOf(Error);
+        expect("code" in err).toBe(false);
+    });
+
+    test("an error with no message keeps the generic fallback", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "eth_sendTransaction" }),
+            { error: { code: REJECTED } },
+        );
+        expect(err.message).toBe("Request failed");
+        expect(err.code).toBe(REJECTED);
+    });
+});
+
+// Every entry point the provider exposes, not just eth_requestAccounts. They
+// all funnel through the same response listener, and this is what says so.
+describe("every request path carries the code", () => {
+    const rejection = {
+        error: { code: REJECTED, message: "User rejected the request." },
+    };
+
+    test("request()", async () => {
+        const err = await rejectionFrom(
+            (p) => p.request({ method: "eth_requestAccounts" }),
+            rejection,
+        );
+        expect(err.code).toBe(REJECTED);
+    });
+
+    test("enable()", async () => {
+        const err = await rejectionFrom((p) => p.enable(), rejection);
+        expect(err.code).toBe(REJECTED);
+    });
+
+    test("send(method, params)", async () => {
+        const err = await rejectionFrom(
+            (p) => p.send("eth_requestAccounts", []),
+            rejection,
+        );
+        expect(err.code).toBe(REJECTED);
+    });
+
+    test("send({ method, params })", async () => {
+        const err = await rejectionFrom(
+            (p) => p.send({ method: "personal_sign", params: ["0x00"] }),
+            rejection,
+        );
+        expect(err.code).toBe(REJECTED);
+    });
+
+    test("sendAsync() hands the code to its callback", async () => {
+        const { provider, respond } = loadProvider();
+        const called = new Promise((resolve) => {
+            provider.sendAsync({ id: 1, method: "eth_requestAccounts" }, (e) =>
+                resolve(e),
+            );
+        });
+        respond(rejection);
+        const err = await called;
+        expect(err.name).toBe("ProviderRpcError");
+        expect(err.code).toBe(REJECTED);
+        expect(err.message).toBe("User rejected the request.");
+    });
+});
+
+describe("the success path is unchanged", () => {
+    test("a result still resolves", async () => {
+        const { provider, respond } = loadProvider();
+        const settled = provider.request({ method: "eth_requestAccounts" });
+        respond({ result: ["0xb61264DEFB0c4B8afb3D73724be15310036743a5"] });
+        await expect(settled).resolves.toEqual([
+            "0xb61264DEFB0c4B8afb3D73724be15310036743a5",
+        ]);
+        expect(provider.selectedAddress).toBe(
+            "0xb61264DEFB0c4B8afb3D73724be15310036743a5",
+        );
+    });
+});