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/cdp/session.ts b/src/cdp/session.ts
index de1ff4b..bf423e1 100644
--- a/src/cdp/session.ts
+++ b/src/cdp/session.ts
@@ -250,7 +250,8 @@ export const createCdpSession = (
         const hw = ownership.harnessWindow();
         if (hw && !live.has(hw)) ownership.setHarnessWindow(undefined);
 
-        if (survivors.length === 0) {
+        const anchorId = survivors[0];
+        if (anchorId === undefined) {
           // No owned tab survived — the harness window is gone (user closed it,
           // or Chrome restarted and reassigned all ids). The persisted windowId
           // is now meaningless and could even collide with one of the user's
@@ -263,7 +264,6 @@ export const createCdpSession = (
           // Ownership is thus DERIVED from the real window, never from the bare
           // persisted integer (which Chrome may reassign to a user window on
           // restart — anchoring on a survivor makes that misfire impossible).
-          const anchorId = survivors[0]!;
           const anchorWin = await getWindowId(session, anchorId);
           if (anchorWin.success) {
             const anchorWindowId = anchorWin.data;