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, 2 insertions, 1 deletions

diff --git a/src/cdp/discovery.ts b/src/cdp/discovery.ts
index b4be31c..dc998b5 100644
--- a/src/cdp/discovery.ts
+++ b/src/cdp/discovery.ts
@@ -8,6 +8,7 @@ import { parseJson } from "../schemas/parse";
 import { type Result, err, ok } from "../util/result";
 import { userDataDirCandidates } from "../profile/paths";
 import { type CdpError, cdpError } from "./errors";
+import { errnoCode } from "../util/guards";
 
 const PORT_PROBE_DEADLINE_MS = 30_000;
 const PORT_PROBE_INTERVAL_MS = 1_000;
@@ -149,7 +150,7 @@ export const discoverEndpoint = async (): Promise<Result<CdpEndpoint, CdpError>>
       // dir is on our list but the user hasn't installed that browser. EPERM/
       // EACCES is common under sandboxes; remember it and fall back to network
       // probing rather than failing the whole discovery.
-      const code = (e as NodeJS.ErrnoException).code;
+      const code = errnoCode(e);
       if (code === "ENOENT" || code === undefined) continue;
       if (code === "EPERM" || code === "EACCES") {
         readErrors.push(`${portFile}: ${code}`);