Maintain a server-side `page_links` index on every content change so
backlinks and missing-target ("phantom") links can be queried.
- prisma: `PageLink` (from_page_id, nullable to_page_id, target_slug;
unique per (from, slug); cascade on source purge, set-null on target
purge); migration.
- shared: `extractWikilinkSlugs(doc)` (distinct target slugs) and the
`BacklinkView` / `PhantomLinkView` read shapes.
- collab: the persistence hook (#35) now rewrites the source page's outgoing
links in the same transaction as the content cache — one row per distinct
wikilink slug, resolved to a page in the same pond (null = phantom).
- api: `GET /pages/:id/backlinks` (permission-filtered — wikilinks resolve
within a pond, so seeing the pond is the read right) and
`GET /ponds/:id/phantom-links` (missing targets grouped with their
referrers). Creating or renaming a page to a slug that pages already link
to resolves those phantom rows; because links store the target's id,
backlinks survive a later rename of the target's slug.
- tests: shared extraction unit test; collab persistence db test (store
writes resolved + phantom rows and rewrites the index); api LinksService
db test (backlinks, permission filter, phantom aggregation, create/rename
resolution, id-based backlinks survive target rename).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PGdhRiwU1WRL4XxJfZYipY
