index: claim one height per steal on the catch-up wave

[rearden-grok]

Summary

• Index assemble waves claim one height. Script-verify waves still claim 32 jobs, which is what left a late window (shorter than 32 heights) on a single rbtc-scripts-* worker.
• Claim size is fixed. Workers loop into the next claim without parking, and the early chain already has several times more read time than build time, so a per-height atomic does not move that band.
• Filters and tweaks are unchanged. No reader, cache, or write-path change.

Host check after merge

Instantaneous rate is the next= delta over the elapsed= delta, not the cumulative rate=.

• Past 800k, build thread time should fall toward read. The 820k–900k band (about 14–17/s on 2026-09-27, build 1.2–1.5× read) should move into the low 20s to about 30/s.
• 200k–600k should stay on the read floor (about 50/s at 400k–600k, higher earlier). A drop there is the early-phase regression this is betting against.
• If build is still the wall past 800k, the follow-up is tx batches inside a height. If build drops under read, the next plan is the reader.

Test plan

• index_wave_claims_one_job: 8 jobs at claim size 1 are 8 claims; the 32-job default covers those 8 in one claim
• steal_chunk_amortizes_claims still expects ~8 claims for 256 script-verify jobs
• Workspace suite, clippy -D warnings, deny, ast-grep, and ci-os-smoke
• Operator host catch-up log after merge

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