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, 2 deletions

diff --git a/src/domains/ref-resolve.ts b/src/domains/ref-resolve.ts
index de83521..a80c620 100644
--- a/src/domains/ref-resolve.ts
+++ b/src/domains/ref-resolve.ts
@@ -2,7 +2,7 @@ import type { BrowserClient } from "../client";
 import { type Result, err, ok } from "../util/result";
 import type { ToolErr } from "../util/tool";
 import { type Box, boxOf } from "./box";
-import { buildTree, collectInteractiveTargets, type RawAxNode, type SlimNode } from "./snapshot";
+import { buildTree, collectInteractiveTargets, type SlimNode } from "./snapshot";
 
 const staleErr = (ref: string): ToolErr => ({
   kind: "invalid_state",
@@ -78,7 +78,7 @@ export const interactiveDiff = async (client: BrowserClient): Promise<string> =>
 
   const axRes = await session.call("Accessibility.getFullAXTree", {});
   if (!axRes.success) return "";
-  const rawNodes = (axRes.data as { nodes: ReadonlyArray<RawAxNode> }).nodes;
+  const rawNodes = axRes.data.nodes;
   const slim = buildTree(rawNodes, { interestingOnly: true, maxNodes: 1000 });
   const targets = collectInteractiveTargets(slim);