The `query_mentioned_in` SQL previously joined notes directly against
the full issues/merge_requests tables, with per-row subqueries for
author/assignee/reviewer exclusion. On large databases this produced
pathological query plans where SQLite scanned the entire notes table
before filtering to relevant entities.
Refactor into a dedicated `build_mentioned_in_sql()` builder that:
1. Pre-filters candidate issues and MRs into MATERIALIZED CTEs
(state open OR recently closed, not authored by user, not
assigned/reviewing). This narrows the working set before any
notes join.
2. Computes note timestamps (my_ts, others_ts, any_ts) as separate
MATERIALIZED CTEs scoped to candidate entities only, rather than
scanning all notes.
3. Joins mention-bearing notes against the pre-filtered candidates,
avoiding the full-table scans.
Also adds a test verifying that authored issues are excluded from the
mentions results, and a unit test asserting all four CTEs are
materialized.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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