[mbreiser]

Summary

• The runlog-index workflow's first full rebuild in the private reiserlab/arena-experiments (147 rig03-sr logs pushed 2026-11-04) failed: the token-authenticated raw host answers a suffix range (bytes=-4096) with 501 Unsupported client range. The public course repo accepted the same request, which is why this never showed before.
• Fix: read the tail as bytes=<size-4096>-<size-1>; the size is already in the contents listing. Verified against the failing file (explicit range returns the real logging_stopped tail). The same change is committed in arena-experiments (062614d), whose script is a copy of this one; this PR keeps the source of truth in step for the next seed-data-repo.sh.
• Tooling script only, no web tool touched. Tier: fine for the next candidate bundle (with Studio/Designer/dashboard default to the private lab data repo; ?repo= tab override; Rig id (LAB-227 Phase 4) #291 + rig harness: gate the host monitor's CPU on the mean (≤ 3 % of a core) #287) or as a tooling-only merge, Michael's call.

Test plan

• pixi run python tests/test-build-runlog-index.py 21/21
• arena-experiments workflow_dispatch rebuild with the patched copy (run 41895568395)

Release notes

(none — repo tooling, not a web tool)

LAB-227

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