feat: centrality "Rediscover" strip over the entity graph (P13e-2)

[blokzdev]

P13e-2 — Centrality "Rediscover"

Second PR of P13e. Resurfaces central-but-stale items — well-connected in the library's web yet not opened in a while — as a "Rediscover" strip on the Dashboard and Library.

Every-device (graph only, no embedder), reusing P13e-1's Cozo pulls. No schema change, no deps.

Algorithm

PageRank, not betweenness: betweenness is O(V·E) — too costly for a query-time strip, and more apt for e-3's path/bridge work (deferred to BACKLOG). PageRank is a cheap, deterministic power iteration that ranks "how woven into the library is this item."

How it works

• centrality.dart (new, pure — sits beside community_clustering.dart) — buildItemGraph(...) builds a weighted undirected item↔item adjacency from the entity graph (each shared uploader/playlist/tag bucket +1, each co-download edge +1; over-generic buckets dropped, the e-1 rule); pageRank(...) is deterministic weighted power iteration with dangling-mass redistribution.
• GraphQueryService.itemCentrality() — id → score over the entity graph; reuses entityMembershipScript()/coDownloadPairsScript() (decode shared with communityClusters via a new private _entityGraph() helper). {} when the store is unavailable.
• rediscover.dart (new, pure) — rankRediscover: score = centrality × staleness, where staleness grows with days since last touch (lastAccessedAt ?? createdAt, capped at 30d); items touched within 14 days are excluded so it never echoes "Recently opened". Top 12, deterministic ordering.
• rediscoverProvider hydrates the scored ids from Drift + ranks them; RediscoverRow (mirrors RecentMediaRow, auto-hides when empty) renders the strip on the Dashboard (below "Recently opened") and atop the Library (only when not searching/filtering/selecting, so it never intrudes).

Tests (CI; native Cozo is APK-verified)

• centrality_test — weight accumulation across shared buckets + co-download, bucket pruning, hub outranks leaf, determinism, dangling-node safety.
• graph_query_service_test — itemCentrality() decode + {} when unavailable.
• rediscover_test — rankRediscover: fresh-exclusion, staleness lifting an older item over a more-central recent one, cap, skip-unknown, empty.
• rediscover_provider_test — fake graph + in-memory Drift (mixed fresh/stale) → central-but-stale items, excluding the freshly-opened one; [] when unavailable.
• rediscover_row_test — renders header + tiles; hidden when empty.
• Full suite green (909 tests), dart format + flutter analyze clean.

Docs

• P13-PLAN.md — e-2 [~] + as-built; GRAPH-SPEC.md §7 — centrality row realized at e-2 (PageRank × staleness; betweenness deferred); VERIFICATION.md — P13e-2 checklist; BACKLOG.md — betweenness, shared item-graph builder extraction, tuning/"See all".

Verification

• ✅ CI gates green locally (format · analyze · 909 tests).
• ⏳ APK spot-check owed (native Cozo): the Rediscover strip surfaces sensible central-but-stale items on Dashboard + Library for an established library, excludes recently-opened items, hides on a fresh library / while filtering / when the graph is off, and works on a low-end device.

Next: e-3 path/bridge discovery + graph-view polish — closes P13e.

https://claude.ai/code/session_013JoYmLCosYt5tQ8qwdbL1T

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