Publish r26.1.0.BETA's tarball to main's permanent download location (release process Step 20).
install_sdp.sh's fixed, permanent SDPURL now resolves to a real, current
tarball for the first time. This is the completion of the 2026-09-02
design discussion: no dead-link window ever existed during this process --
main's downloads/ was untouched (isolate'd) through Copy Up and all
subsequent steps, so the fixed URL was always serving something real; this
is simply the deliberate switch from serving nothing (first-ever release,
so there was no 'previous' tarball) to serving 2026.1 for real.
Agent: Claude Code, Model: Claude Sonnet 5 (claude-sonnet-5), operating as bot_Claude_Anthropic.