A scan fetches six feeds ahead of its turn, so channels next to each
other alphabetically (android-authority-2, android-developers, apple,
architectural-digest-2) went to YouTube together and failed together,
while one asked alone a minute later read. feed::fetch now takes a turn
before each request for a YouTube feed: one at a time per process, two
seconds after the last, its wait a `youtube_turn` span. The retries
take their turn too, in place of their one-second sleep. The directory
builds the same fetch and paces its own checks the same way.
39 channels due together add up to 80 s to that scan.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
rays
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