thumb2c batch: score registered owners inside retained regions (--owner-spans, --sweep)

[wowwheaties]

Summary

thumb2c batch scores each retained region at its extent, but many regions hold more than one registered owner (regions.json manual_regions). Scoring the unchanged draft at the owner's own span instead often links exact already — that observation produced most of the owners in #6, by hand. This makes thumb2c do it (supersedes #7, which targeted the removed lifter).

• --owner-spans (batch, list): after the region pass, score every registered owner whose start lies inside the region at that owner's span; one row per owner (resource_3a2:02000924 span=412 differing_halfwords=6 (region 02000924 extent 1036)) and an owner_spans=… owner_exact=… summary line.
• --sweep: when the owner span is not exact, retry with the span widened to the rest of the region and report both (sweep_span=… best=owner|sweep), for owners registered short of the pool island their function really runs to (the 3c5:02001238 / 379:02000074 shape from ☀️ 74% – adopt seventy-four exact owners on 7d8a72083: eight main-image functions and sixty-six scene sequences #6).
• trailing pad: a reference exactly one halfword longer than the candidate with wrong_instructions=0 is ranked exact and marked trailing_pad=1 with the raw count kept in the row; adopt still decides on the real bytes.

Default output is byte-identical without the flags. No new dependencies; cargo test and cargo fmt --check clean; make verify green.

On this tree (187bb97)

thumb2c batch --all --jobs 8 --owner-spans --sweep: 184 regions, 270 owner spans, 51 exact from the unchanged draft (one via the pad rule: 3a6:020011a0), 12 spans where the widened sweep scores better than the registered span. Of the 386 overlay-assembly regions, 64 nest two or more registered owners; those are the ones the region-extent pass could not see.

Notes

• Under --jobs 8 a handful of owner scores come back with no score line (23 here); each scores fine when retried alone. That is the existing scorer subprocess path under load, not new code — left as is rather than adding a retry you might prefer to shape.
• The sweep widens to the region end only. Widening to the next registered owner start would be a natural refinement if you want the tool to propose the corrected span for the registry.