GitHub Pages deploy verification

Problem

Three failure modes when verifying that a deploy is live via curl:

1. False-positive poll predicate. Polling until curl ... | grep -q "<selector>"; do sleep; done succeeds instantly if the selector existed before the deploy too. The loop exits on the OLD content; you think you've verified the new state and you haven't.

2. Blocked timing chain. sleep 35 && curl ... looks reasonable but the Claude Code harness blocks long leading sleeps inside Bash to prevent dead polling. Worse, even short sleep N && curl followed by additional pipes can hit "Blocked: sleep N followed by:" errors that cancel parallel tool calls.

3. Unbounded failure. A missing marker can mean a slow deploy, failed build, HTTP error, or stale content. An endless loop distinguishes none of them and cannot return a useful verdict.