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/snapshot.test.ts

@@ -1,6 +1,8 @@
 import { describe, expect, it, vi } from "vitest";
+import sharp from "sharp";
 import type { CameraDevice, Snapshot } from "@parking/devices";
-import { captureSnapshotShared } from "./snapshot.js";
+import { captureSnapshotShared, encodeForStorage } from "./snapshot.js";
+import { silentLogger } from "./test-helpers.js";
 
 // captureSnapshotShared: one HTTP pull per camera per vehicle. A Hikvision unit serves
 // snapshots SINGLE-THREADED (a 2nd concurrent GET → HTTP 503). On an entry the ANPR
@@ -91,3 +93,49 @@ describe("captureSnapshotShared", () => {
     expect(s1.bytes.equals(s2.bytes)).toBe(false);
   });
 });
+
+// encodeForStorage: downscale + re-compress a captured frame for STORAGE (smaller, plate
+// still readable). Recognition uses the original; this never runs on the OCR path. Fail-soft.
+describe("encodeForStorage", () => {
+  /** A big synthetic JPEG (2688×1520, the Hikvision main-stream size) to downscale. */
+  async function bigJpeg(): Promise<Buffer> {
+    return sharp({
+      create: { width: 2688, height: 1520, channels: 3, background: { r: 120, g: 130, b: 140 } },
+    })
+      .jpeg({ quality: 95 })
+      .toBuffer();
+  }
+
+  it("downscales the long edge to ≤1280 and emits clean image/jpeg", async () => {
+    const bytes = await bigJpeg();
+    const shot: Snapshot = { bytes, contentType: 'image/jpeg; charset="UTF-8"', capturedAt: new Date().toISOString() };
+    const out = await encodeForStorage(shot, silentLogger());
+    expect(out.contentType).toBe("image/jpeg"); // charset cruft stripped
+    const meta = await sharp(out.bytes).metadata();
+    expect(Math.max(meta.width ?? 0, meta.height ?? 0)).toBeLessThanOrEqual(1280);
+    expect(out.bytes.length).toBeLessThan(bytes.length); // smaller than the original
+  });
+
+  it("never enlarges an already-small image", async () => {
+    const small = await sharp({ create: { width: 640, height: 360, channels: 3, background: { r: 0, g: 0, b: 0 } } })
+      .jpeg()
+      .toBuffer();
+    const out = await encodeForStorage(
+      { bytes: small, contentType: "image/jpeg", capturedAt: new Date().toISOString() },
+      silentLogger(),
+    );
+    const meta = await sharp(out.bytes).metadata();
+    expect(meta.width).toBe(640); // withoutEnlargement
+    expect(meta.height).toBe(360);
+  });
+
+  it("fails soft: a non-image body is stored unchanged with a cleaned type", async () => {
+    const garbage = Buffer.from("this is not an image");
+    const out = await encodeForStorage(
+      { bytes: garbage, contentType: 'text/plain; charset="UTF-8"', capturedAt: new Date().toISOString() },
+      silentLogger(),
+    );
+    expect(out.bytes.equals(garbage)).toBe(true); // original bytes, never dropped
+    expect(out.contentType).toBe("text/plain"); // charset stripped even on the fallback
+  });
+});