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, 18 insertions, 1 deletions

diff --git a/src/state.ts b/src/state.ts
index d4b1534..601f7e0 100644
--- a/src/state.ts
+++ b/src/state.ts
@@ -6,6 +6,7 @@
  */
 
 import type { ExtensionAPI, ExtensionContext } from "@mariozechner/pi-coding-agent";
+import { asArrayOf, asNumber, asString, isRecord } from "./util/guards";
 
 export type BrowserState = {
   readonly namespace: string;
@@ -31,13 +32,29 @@ export const persistState = (pi: ExtensionAPI, state: BrowserState): void => {
  * If `currentNamespace` is supplied (e.g. from the --browser-namespace flag),
  * it overrides whatever is in the persisted entry.
  */
+const asPersistedState = (v: unknown): Partial<BrowserState> | undefined => {
+  if (!isRecord(v)) return undefined;
+  const namespace = asString(v["namespace"]);
+  const remoteBrowserId = asString(v["remoteBrowserId"]);
+  const ownedTargetIds = asArrayOf(v["ownedTargetIds"], asString);
+  const harnessWindowTargetId = asString(v["harnessWindowTargetId"]);
+  const harnessWindowId = asNumber(v["harnessWindowId"]);
+  return {
+    ...(namespace !== undefined ? { namespace } : {}),
+    ...(remoteBrowserId !== undefined ? { remoteBrowserId } : {}),
+    ...(ownedTargetIds !== undefined ? { ownedTargetIds } : {}),
+    ...(harnessWindowTargetId !== undefined ? { harnessWindowTargetId } : {}),
+    ...(harnessWindowId !== undefined ? { harnessWindowId } : {}),
+  };
+};
+
 export const restoreState = (ctx: ExtensionContext, currentNamespace?: string): BrowserState => {
   const branchEntries = ctx.sessionManager.getBranch();
   const fallback = defaultState(currentNamespace);
   for (let i = branchEntries.length - 1; i >= 0; i--) {
     const entry = branchEntries[i];
     if (entry?.type === "custom" && entry.customType === "browser-harness-state") {
-      const data = entry.data as Partial<BrowserState> | undefined;
+      const data = asPersistedState(entry.data);
       if (data) {
         return {
           ...fallback,