refactor(cdp): extract attachTo, getWindowId, evaluateJson helpers

Target.attachToTarget was decoded at 5 sites, Browser.getWindowForTarget
at 5, and Runtime.evaluate unwrapped at another. Each is now one typed
helper. Deletes the dead cdp/window-binding.ts.

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

1 files changed, 31 insertions, 0 deletions

diff --git a/src/cdp/evaluate.ts b/src/cdp/evaluate.ts
new file mode 100644
index 0000000..cd68d61
--- /dev/null
+++ b/src/cdp/evaluate.ts
@@ -0,0 +1,31 @@
+import { type Result, err, ok } from "../util/result";
+import { type CdpError, cdpError } from "./errors";
+import type { CdpSession } from "./session";
+
+/**
+ * Runtime.evaluate, unwrapped and narrowed. Runs `expression`, surfaces a page
+ * exception as an error, then applies `check` to the returned value — the
+ * sanctioned way to turn `unknown` evaluate output into a typed `T` without a
+ * cast.
+ */
+export const evaluateJson = async <T>(
+  session: CdpSession,
+  expression: string,
+  check: (v: unknown) => v is T,
+): Promise<Result<T, CdpError>> => {
+  const r = await session.call("Runtime.evaluate", {
+    expression,
+    returnByValue: true,
+    awaitPromise: true,
+  });
+  if (!r.success) return r;
+  const { result, exceptionDetails } = r.data;
+  if (exceptionDetails !== undefined) {
+    return err(cdpError("remote_error", exceptionDetails.text, "Runtime.evaluate"));
+  }
+  const value = result.value;
+  if (!check(value)) {
+    return err(cdpError("invalid_response", `unexpected evaluate shape for: ${expression.slice(0, 60)}`, "Runtime.evaluate"));
+  }
+  return ok(value);
+};