feat(node): cap the media cache and evict least-recently-used entries

2026-09-08T11:21:02Z

`thumbs` holds every generated thumbnail, every TMDB poster and backdrop, every Cover Art Archive image and every cached audio transcode. Rows were removed only when their source file left every group's index (`prune_file`), so a library that merely changes over years grew this database with nothing to bound it. Nothing in it is precious — every row is keyed off a value the node can re-derive — which is what makes eviction the right answer rather than a bigger disk. 512 MB, evicted on write (a cache only grows when written to; a timer is one more thing to own and get wrong). `used_at` is marked on every read, including the lookup by synthetic id that `_fetch_and_cache_poster` makes on every visit to a poster grid — without that, the images shown most often would be the coldest rows in the table. A single blob larger than the cap does not empty the table for nothing. The migration is the part that touches deployed nodes. `CREATE TABLE IF NOT EXISTS` adds missing tables and never missing columns, so `used_at` would have reached a fresh test database and never a real one. `_migrate()` does the ALTER TABLE and seeds existing rows with "now" rather than 0 — otherwise the first write after an upgrade evicts the whole cache, a correct-but-hostile reading of "least recently used" for rows whose age nothing recorded. The index on that column lives in `_migrate()`, not in `_SCHEMA`: run from the schema script it executes before the ALTER on an existing database and fails, which would have been every deployed node refusing to open its cache on the first start after upgrading. Found by the migration test. Verified against a real node's database, rebuilt into its pre-migration shape: rows preserved, column present, seeded, index created, reopening harmless. Co-Authored-By: Claude Opus 5 Claude-Session: https://claude.ai/code/session_01HCGdheDLxGReuKHga3BtST

meshbay.git/packages/meshbay-node/tests/test_media_cache_eviction.py, branch 0.14

feat(node): cap the media cache and evict least-recently-used entries