-- t-paliad-171 — SmartTimeline Slice 1.
-- Add the `timeline_kind` opt-in column to paliad.project_events so a
-- subset of audit rows can surface as timeline content. Existing rows
-- stay NULL (audit-only) and are filtered out of the SmartTimeline
-- read path; new write paths (custom milestone, counterclaim_created
-- in later slices) set the column on insert.
--
-- Value space (enforced in code, not via CHECK — see
-- internal/services/projection_service.go):
--   'milestone'        — structural event worth pinning to the timeline
--                        (counterclaim_filed, third_party_intervened,
--                         party_amendment, our_side_changed, scope_change)
--   'custom_milestone' — free-text user-added event ("Eigener Meilenstein")
--   NULL               — audit only (default, all existing rows)
--
-- Design ref: docs/design-smart-timeline-2026-05-08.md §2.2.

ALTER TABLE paliad.project_events
    ADD COLUMN IF NOT EXISTS timeline_kind text NULL;

COMMENT ON COLUMN paliad.project_events.timeline_kind IS
    'When non-NULL, this audit event also surfaces as a SmartTimeline '
    'milestone. NULL keeps the row audit-only. See '
    'internal/services/projection_service.go for the value space.';

-- Partial index — the SmartTimeline read path filters on
-- (project_id, timeline_kind IS NOT NULL); making the index partial
-- keeps it tiny (most rows stay audit-only) while still serving the
-- common lookup.
CREATE INDEX IF NOT EXISTS project_events_timeline_kind_idx
    ON paliad.project_events (project_id, timeline_kind)
    WHERE timeline_kind IS NOT NULL;