refactor: close the remaining unguarded type assertions

Types the event-queue iterator's TReturn as undefined so the terminal
result needs no cast; declares the isError field the pi runtime reads by
duck-typing; binds socket to a local const in the daemon transport;
replaces the @ts-ignore on the optional sharp import with a non-literal
specifier so src/ still typechecks where sharp was not installed.

Adds src/util/guards.ts as the single home for narrowing over unknown —
isRecord plus scalar/array readers — and converts the two private
isObject copies in cdp/types.ts and daemon/protocol.ts along with every
inline `as Record<string, unknown>` in domains/js.ts and domains/render.ts.

Gives Accessibility.getFullAXTree a real result schema, closing the last
unvalidated CDP boundary: only nodeId is required, every object carries
additionalProperties, and each AX value stays Unknown, so the tree
decodes as a whole or fails as a whole rather than being filtered.

Guards the five tool-result `details` readers, the daemon attach
response, the persisted session state, the browser-namespace flag, and
the fs errno narrowing, each feeding an already-present failure path.

The daemon-transport socket binding is not a bug fix: send() runs
synchronously inside sendWithTimeout's promise executor, so socket cannot
be reassigned between the check and the write. It removes the assertion
and makes the write immune to a later refactor that adds an await.

Two assertions survive by design and are documented in the task report:
the never->unknown re-widening in util/tool.ts, which the type-erased
tool registry makes unavoidable, and the AsyncFunction constructor lookup
in domains/js.ts, which JavaScript exposes no typed binding for.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1 files changed, 95 insertions, 0 deletions

diff --git a/test/util/guards-test.ts b/test/util/guards-test.ts
new file mode 100644
index 0000000..7c7b426
--- /dev/null
+++ b/test/util/guards-test.ts
@@ -0,0 +1,95 @@
+import { test, describe } from "node:test";
+import assert from "node:assert/strict";
+import { asArrayOf, asBoolean, asNumber, asRecord, asString, errnoCode, isRecord } from "../../src/util/guards";
+
+describe("isRecord", () => {
+  test("accepts plain objects", () => {
+    assert.equal(isRecord({}), true);
+    assert.equal(isRecord({ a: 1 }), true);
+  });
+
+  test("rejects null, arrays and primitives", () => {
+    assert.equal(isRecord(null), false);
+    assert.equal(isRecord(undefined), false);
+    assert.equal(isRecord([]), false);
+    assert.equal(isRecord([{ a: 1 }]), false);
+    assert.equal(isRecord("s"), false);
+    assert.equal(isRecord(0), false);
+    assert.equal(isRecord(false), false);
+  });
+});
+
+describe("scalar readers", () => {
+  test("asString accepts only strings", () => {
+    assert.equal(asString(""), "");
+    assert.equal(asString("x"), "x");
+    assert.equal(asString(1), undefined);
+    assert.equal(asString(null), undefined);
+    assert.equal(asString(undefined), undefined);
+    assert.equal(asString({}), undefined);
+  });
+
+  test("asNumber accepts only numbers, including 0 and NaN", () => {
+    assert.equal(asNumber(0), 0);
+    assert.equal(asNumber(-1.5), -1.5);
+    assert.equal(Number.isNaN(asNumber(Number.NaN)), true);
+    assert.equal(asNumber("1"), undefined);
+    assert.equal(asNumber(null), undefined);
+  });
+
+  test("asBoolean accepts only booleans", () => {
+    assert.equal(asBoolean(false), false);
+    assert.equal(asBoolean(true), true);
+    assert.equal(asBoolean(0), undefined);
+    assert.equal(asBoolean("true"), undefined);
+  });
+
+  test("asRecord mirrors isRecord but yields the value", () => {
+    assert.deepEqual(asRecord({ a: 1 }), { a: 1 });
+    assert.equal(asRecord([]), undefined);
+    assert.equal(asRecord(null), undefined);
+  });
+});
+
+describe("asArrayOf", () => {
+  test("parses every element", () => {
+    assert.deepEqual(asArrayOf(["a", "b"], asString), ["a", "b"]);
+    assert.deepEqual(asArrayOf([], asString), []);
+  });
+
+  test("rejects the whole array when any element fails, rather than dropping it", () => {
+    assert.equal(asArrayOf(["a", 2], asString), undefined);
+    assert.equal(asArrayOf([1, "b"], asString), undefined);
+  });
+
+  test("rejects non-arrays", () => {
+    assert.equal(asArrayOf({ 0: "a" }, asString), undefined);
+    assert.equal(asArrayOf(undefined, asString), undefined);
+    assert.equal(asArrayOf("ab", asString), undefined);
+  });
+
+  test("treats an element parsed as undefined as a failure", () => {
+    assert.equal(asArrayOf([undefined], asString), undefined);
+  });
+});
+
+describe("errnoCode", () => {
+  test("reads .code off a real Error", () => {
+    const e = Object.assign(new Error("nope"), { code: "ENOENT" });
+    assert.equal(errnoCode(e), "ENOENT");
+  });
+
+  test("returns undefined for an Error without a code", () => {
+    assert.equal(errnoCode(new Error("plain")), undefined);
+  });
+
+  test("returns undefined for a non-string code", () => {
+    assert.equal(errnoCode(Object.assign(new Error("x"), { code: 13 })), undefined);
+  });
+
+  test("returns undefined for non-Errors that merely carry a code", () => {
+    assert.equal(errnoCode({ code: "ENOENT" }), undefined);
+    assert.equal(errnoCode("ENOENT"), undefined);
+    assert.equal(errnoCode(null), undefined);
+  });
+});