feat(snapshot): re-encode captures + disk-pressure retention

Camera snapshots were stored RAW — the camera's full-res JPEG straight into
the BLOB, no resize/recompress. Measured on the dev DB: 300 snapshots = 81.7 MB
= ~72% of the 114 MB SQLite file (the big ones 2688×1520 / ~600 KB, Hikvision
main stream). They dominated the appliance's single backed-up DB file.

Re-encode on capture (snapshot.ts):
- Downscale each frame to SNAPSHOT_MAX_EDGE (1280px long edge) + recompress at
  SNAPSHOT_JPEG_QUALITY (80) via sharp (libvips, Apache-2.0) before storage —
  ~6-10× smaller (verified 2688×1520 → 1280×724, ~8×), plate still readable,
  clean image/jpeg (drops the camera's charset cruft). STORAGE-ONLY: recognition
  keeps the ORIGINAL full-res bytes (downscaling hurts OCR). Fail-soft — a
  re-encode error stores the original, never drops the snapshot or blocks the
  (already-open) path. sharp lives in apps/server (owns the capture path), where
  bcrypt already establishes the native-dep pattern.

Disk-pressure retention (snapshot-retention.ts) — a SAFETY VALVE, not the daily
mechanism (the re-encode does that). Daily check reads the DB filesystem used%
(statfs on db.$client.name); no-op unless ≥ SNAPSHOT_DISK_HIGH_PCT (70). Over the
mark: delete the OLDEST until an estimated SNAPSHOT_DISK_FREE_TARGET_PCT (10%) of
disk is freed — never below SNAPSHOT_MIN_KEEP (500) — then VACUUM once to return
space to the OS. A DELETE only frees SQLite pages (disk doesn't drop until VACUUM),
so the loop is driven by estimated freed bytes (SUM(length(bytes))), not a live
disk re-read; the prune owns the DB-locking VACUUM, run daily off-peak. diskUsage
is injectable for tests. None of this touches the signed ledger — snapshots are
unsigned/advisory, referenced only by id.

Tests: encodeForStorage (downscale / clean-type / no-enlarge / fail-soft) +
pruneSnapshots (no-op below mark / delete-oldest-to-target + VACUUM / MIN_KEEP
floor / skip-VACUUM-when-empty). All four snapshot env knobs documented in the
komodo env reference. Full workspace build/lint/test green; the prune smoke-verified
on a scratch DB copy (file shrank after VACUUM).

Existing ~81.7 MB of raw snapshots are unchanged (a one-off re-encode backfill is
a separate optional follow-up). Updated entry-exit-points + technology-stack wiki.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/server/src/server.ts

@@ -20,6 +20,7 @@ import { PrinterMonitor } from "./printer-monitor.js";
 import { DeviceMonitor } from "./device-monitor.js";
 import { buildSigner, buildVerifier } from "./signer.js";
 import { LogService, pinoDbStream } from "./log-service.js";
+import { pruneSnapshots } from "./snapshot-retention.js";
 import { logRoutes } from "./routes/logs.js";
 import { VisionClient } from "./vision-client.js";
 import { authRoutes } from "./routes/auth.js";
@@ -283,6 +284,23 @@ export async function buildServer(opts: BuildOptions = {}): Promise<FastifyInsta
   logService.prune(); // once at startup
   app.addHook("onClose", async () => clearInterval(pruneTimer));
 
+  // Snapshot retention prune — DISK-PRESSURE safety valve: only when the DB's filesystem
+  // crosses the high-water mark do we delete the oldest snapshots + VACUUM. A no-op the rest
+  // of the time. Daily, unref'd, plus once at startup. See snapshot-retention.ts.
+  const runSnapPrune = async () => {
+    const res = await pruneSnapshots(db, {}, app.log);
+    if (res.deletedRows > 0) {
+      app.log.info(
+        `pruned ${res.deletedRows} snapshots, freed ~${(res.freedBytesEst / 1048576).toFixed(0)} MB ` +
+          `(disk was ${res.usedPctBefore.toFixed(0)}% used${res.vacuumed ? ", vacuumed" : ""})`,
+      );
+    }
+  };
+  const snapPruneTimer = setInterval(() => void runSnapPrune(), 24 * 60 * 60 * 1000);
+  snapPruneTimer.unref();
+  void runSnapPrune(); // once at startup
+  app.addHook("onClose", async () => clearInterval(snapPruneTimer));
+
   // Recycle-bin retention sweep: auto-purge master data soft-deleted longer than the
   // retention window (RECYCLE_BIN_RETENTION_DAYS, default 30; 0 = keep forever). Runs
   // every 6h, unref'd, plus once at startup. See recycle-bin.ts.