Rewrites the activity feed query to group consecutive events on the same
(actor, document, kind) into sessions separated by >120 min gaps. A session
becomes one row with count = events-in-session and happenedAtUntil = last
event timestamp. Singletons keep count=1 / happenedAtUntil=null.
Algorithm: LAG() to get the previous event's timestamp in the same partition,
mark a new session when gap > 7200s, then SUM() over an unbounded preceding
window yields a running session_id. Aggregation groups by session_id.
COMMENT_ADDED and MENTION_CREATED always start a new session — these kinds
never roll up so each event stays its own row.
Also adds BLOCK_REVIEWED to the eligible-kinds WHERE clause (Chronik spec §02)
so reviewed blocks appear in the activity feed.
Five new integration tests cover combine-within-2h, split-at-boundary,
no-hard-cap-on-long-session, never-rolls-up-comments/mentions, and the
count/happenedAtUntil contract on both singletons and rollups.
Part of #285.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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