The IntersectionObserver-based spy only fired when a section entered a
narrow band 40–45% down the viewport. Short sections at the tail of a
page — Operator key and Roadmap on theseus.x/extensions, whatever came
last on the other pages — never made it into that band because the
page runs out of scroll before their top crosses 40%, so their sidebar
links stayed dim no matter how far the reader scrolled.
Rewrote the spy across every page with a sidebar (theseus.x home /
plug-ins / extensions and sirius.x home / tld / theseus / docs / admin
/ brand): it listens to window scroll, picks the last section whose
top has crossed 35% of the viewport, and — when the window is scrolled
to within 4px of the bottom — snaps to the final section regardless of
where its top is. Every link in the rail can now activate.
theseus.x/extensions also had the spy IIFE bundled with the manifest
loader in one <script> block near the middle of the page, so at run
time the parser hadn't yet reached the last three sections and only
Bundled/Community/Build were ever registered. Moved the spy to its own
<script> just before </body> so it sees every section that ships.
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