POST /claude-usage now merges every day of the sanitized snapshot except
the last one (today, still open) into <dir of CLAUDE_USAGE_PATH>/history/
YYYY-MM.json, after the snapshot itself is written. The latest snapshot
wins, so a day leaving the 30-day window keeps the value the agent froze
at D+2. Each month file is written atomically (same-dir temp, mode 600,
rename). A month file that cannot be read back is never overwritten, and
an archive failure is logged (months and error codes only) without
changing the 204.
GET /claude-usage/history?from=YYYY-MM&to=YYYY-MM (read token) serves the
archived days, defaulting to the 12 months up to the last archived month,
400 on a bad format, from > to or a span over 36 months. Month files are
re-read through the snapshot's per-day whitelist, now exported from
claude-usage.js as sanitizeDay().
The new module also carries the one-shot import command used by the
backfill (`node claude-usage-history.js --import <file|->`), where an
already archived date always wins.
Refs #55
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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