build: Phase 2 — stop emitting unused .blockmap + clean dist per build

- L83: nsis.differentialPackage: false — the custom updater does full
  downloads and never consumes the differential blockmap, so don't generate it
  (NsisTarget gates blockmap generation on differentialPackage !== false).
- L84: add clean:dist script (fs.rmSync) run at the front of build:win so dist/
  no longer accumulates old-version installers (~3 GB observed). dist/out were
  already gitignored, so this is local-disk hygiene.

Config only; TS gate unaffected. 137 -> 135 open audit items.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CODE-AUDIT.md

@@ -637,11 +637,16 @@ token system + shared primitives (UI/SIMP — high value, larger effort) · i18n
   sketch now carries the shipped `videoId`/`itemCount`/`watched`/`feedUrl` fields (plus the
   required `url`/`playlistTitle`/`playlistIndex`) and a note that the block reflects the shipped
   `shared/ipc.ts` shape.*
-- [ ] **L83 — Dead build artifacts.** electron-builder emits `.blockmap` differential-update files
+- [x] **L83 — Dead build artifacts.** electron-builder emits `.blockmap` differential-update files
   for each NSIS installer, but the custom [updater.ts](src/main/updater.ts) does a full download and
-  never consumes them.
-- [ ] **L84 — `dist/` accumulates unboundedly.** ~620 MB per build with no cleanup; it currently
-  holds 0.1.0–0.5.0 Setup + portable artifacts (~3 GB). Add a clean step or prune.
+  never consumes them. *Fixed: `nsis.differentialPackage: false` in
+  [electron-builder.yml](electron-builder.yml) stops the blockmap being generated (NsisTarget gates it
+  on `differentialPackage !== false`), with a comment explaining the custom-updater rationale.*
+- [x] **L84 — `dist/` accumulates unboundedly.** ~620 MB per build with no cleanup; it currently
+  holds 0.1.0–0.5.0 Setup + portable artifacts (~3 GB). Add a clean step or prune. *Fixed: a
+  `clean:dist` npm script (`fs.rmSync('dist', …)`) now runs at the front of `build:win`, so each
+  packaged build starts from an empty `dist/` and only the current version's artifacts remain.
+  (`dist`/`out` were already gitignored, so this is disk hygiene, not a repo change.)*
 - [x] **L85 — `.claude/launch.json` is committed and misplaced.** A VS Code launch config lives in
   `.claude/` (VS Code reads `.vscode/launch.json`), so no tool consumes it; it's also tracked
   (not gitignored).

electron-builder.yml

@@ -68,4 +68,7 @@ nsis:
   perMachine: false
   allowToChangeInstallationDirectory: true
   deleteAppDataOnUninstall: false
+  # The custom updater (src/main/updater.ts) does a full download and never consumes
+  # the differential .blockmap, so don't emit it (audit L83 — dead build artifact).
+  differentialPackage: false
   # Flip perMachine to true for an all-users install to Program Files (requires admin).

package.json

@@ -19,7 +19,8 @@
     "ui:build": "vite build",
     "ui:preview": "vite preview",
     "build": "electron-vite build",
-    "build:win": "electron-vite build && electron-builder --win",
+    "clean:dist": "node -e \"require('fs').rmSync('dist',{recursive:true,force:true})\"",
+    "build:win": "npm run clean:dist && electron-vite build && electron-builder --win",
     "start": "electron-vite preview",
     "typecheck:node": "tsc --noEmit -p tsconfig.node.json --composite false",
     "typecheck:web": "tsc --noEmit -p tsconfig.web.json --composite false",