File downloads get a separate time limit for the server's first reply

One of Claude Code's helpers for downloading files changed in two ways:

• It accepts a time limit for how long to wait for the response headers, the first part of the server's reply that arrives before the file itself. Once the headers arrive, it restarts the timer that detects a stalled download. Before, it used one fixed timeout that was refreshed while data streamed in.
• If it cannot build the address to download from, it returns a failure result instead of raising an error.