Fix name_usage index defects found reviewing #712's fixes

[derek73]

Follow-up to #712, which was merged before this round so another session could proceed. A second review of #712's fix commits found these defects in tools/name_usage.py's CJK index. All are in the dev tool; none changes parsing.

Fixes

• A complete index read as missing. A batch that overran under a new listing was cached as halves, but the old whole-batch file stayed beside them and was read first. A complete index then loaded as missing offline, and every online run re-sent the overrunning query. The halved marker is now read first, and the old file is removed when a batch is halved.
• Batches were keyed by their first and last item. A re-listing that changed an item in between raised "unusable", or silently missed the new item. Each batch file now carries a digest of its whole membership and is fetched again when that changes.
• --refresh-index failed silently with only Latin words. It deleted the index and, if the rebuild failed, exited 0 with nothing said. The failure is now printed and the exit status is 2.
• HTTPErrors are closed on every path where the report discards one: the Wikidata row, the ends-with row, a pairing count and a source loader. Python 3.14 warns on one left open, and Peel the #671 credential words off a glued name, except 部長; name_usage answers ends-with for CJK #712 closed only the retry and overrun paths.
• Extension H. _CJK_CHARS now reaches Extension H, and a redundant range is dropped. INDEX_VERSION is now 3, so an existing cache is rebuilt.

Tests

The new tests cover:

• a cache built before versioning (no version file);
• a batch whose first, last or middle item changed;
• the stale whole batch beside its halves;
• corrupt batch shapes, and a listing with no item column;
• the pairing-count union with the larger chunk first, which a "last chunk wins" bug would pass;
• closed HTTPErrors on each path;
• the refresh failure.

Results:

• Tool tests: 124 pass on 3.11, 3.14 and 3.15.
• Full suite: passes; mypy and ruff are clean.

Index rebuild

The version-3 rebuild ran clean: it detected the old cache and rebuilt it, and one batch that timed out was split in half. The results match #712's: 215,820 entries; 殿 ends 13 name items; the only name item ending in any #707 word is 二世's mislabel 厄德二世 (Q18339792); and every family/given pair counts 0 people.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.03%. Comparing base (901ab66) to head (5d87b22).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #714   +/-   ##
=======================================
  Coverage   99.03%   99.03%           
=======================================
  Files          46       46           
  Lines        4557     4557           
=======================================
  Hits         4513     4513           
  Misses         44       44           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.