Ports main.py's _combat_session_delta / _combat_merge_into_lifetime (incl. the
documented "offense/defense use latest, additively" quirk) and the combat_stats
handler (session delta -> DB-backed lifetime merge -> delete-then-insert of
combat_stats + combat_stats_sessions). Read handlers gain the live combat
overlay (union live + DB), like Python.
Validation:
- combat.go `combat-merge` CLI folds snapshots through the accumulator; diffed
against the Python functions on identical input -> byte-IDENTICAL.
- combat_test.go golden test runs in the build (go test now part of the tracker
Dockerfile).
- Live: 40 combat lifetime rows + 40 session snapshots + rare_events flowing in
dereth_go via the shadow consumer.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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