Concurrent captures are bound by how many distinct partner sites we can
drive in parallel — each capture needs its own site so they don't collide
on the synchronous siteIndex round-robin. Ports are effectively unlimited
(10000-10999) and Playwright contexts are isolated, so the previous
arbitrary cap of 3 left headroom on the table when the pool is cold and
N>3 user clicks race in at once.
Tying the cap to JWT_SITES.length also means future site additions or
removals auto-adjust the ceiling.
Semih Yesilyurt
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