Harden audit findings: correctness, type-safety, Windows conventions & polish

Audit-pass over CODE-AUDIT.md (~48 items closed this pass; all verified —
typecheck + 234 tests + eslint + prettier green).

Correctness / bugs:
- B3: match the release checksum to the asset's filename line (no wrong-hash verify)
- B4: newline-safe metadata probe (one --print with a unit-separator delimiter)
- B5 / L88: guard the meta event against canceled items; progress no longer promotes
  a queued item outside pump()
- B7: cookie-login promise always resolves (handles destroy-without-close)
- L146: trim parser rejects >2 colon-group times; M36: Library selection counts only
  actionable rows
- L11 / L50 / L156 / L57 / L159 / L15 / L3: live queue count, empty-cookie message,
  schedule picker min, dead-code/comment cleanup

Type safety:
- Enable noUncheckedIndexedAccess + noFallthroughCasesInSwitch (15 real edge cases fixed)

Resilience / Windows / metadata:
- R5: settings write failure handled (no unhandled IPC rejection; reconciles to truth)
- W1 / W5 / W6: min window size, seeded folder picker, parented sign-in window;
  L147 dead macOS branches removed
- CL1: shared stdout markers; package/builder metadata (license, homepage, repository,
  copyright, tsbuildinfo glob)

Copy / docs / tests:
- M37 / SR9 dev-jargon cleanup in hints; M8 / M25 / M26 / L66 / L80 / L81 reconciled
- New unit tests for L35 (isValidMediaItem) and L36 (compareVersions)

This commit also checkpoints the previously-uncommitted feat/tray-background-clipboard
work it builds on: background running + auto-download, library clipboard detection,
tray, binary management & library scale, credential encryption at rest, the shared
jsonStore and ui/ primitives, and the eslint/prettier tooling.

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

src/main/sources.ts

@@ -12,48 +12,27 @@
  * can't feed the UI malformed records (same approach as history/errorlog).
  */
 
-import { app } from 'electron'
-import { join } from 'path'
-import { readFileSync, writeFileSync, existsSync } from 'fs'
 import type { Source, MediaItem } from '@shared/ipc'
 import { isValidSource, isValidMediaItem } from './validation'
 import { mergeItemsPreservingState } from './indexerCore'
+import { createJsonStore } from './jsonStore'
 
 // A generous global cap so a runaway index can't grow the file unbounded; large
 // enough for several big channels. When exceeded, the most-recently-written
 // source's items are kept (they're placed first by replaceMediaItems).
 const MAX_ITEMS = 20000
 
-function sourcesFile(): string {
-  return join(app.getPath('userData'), 'sources.json')
-}
-
-function itemsFile(): string {
-  return join(app.getPath('userData'), 'media-items.json')
-}
-
-function readJsonArray<T>(path: string, isValid: (o: unknown) => o is T): T[] {
-  try {
-    if (!existsSync(path)) return []
-    const data = JSON.parse(readFileSync(path, 'utf8'))
-    return Array.isArray(data) ? data.filter(isValid) : []
-  } catch {
-    return []
-  }
-}
-
-function writeJson(path: string, value: unknown): void {
-  try {
-    writeFileSync(path, JSON.stringify(value, null, 2))
-  } catch {
-    /* best-effort; a read-only data dir just means no persisted index */
-  }
-}
+// Two cached, atomically-written stores (R1–R3 via the shared jsonStore). The
+// media-items store is the hot path: setMediaItemDownloaded used to re-read and
+// rewrite the whole (≤MAX_ITEMS) file on every completion; now reads hit the
+// cache and writes are batched. Sources are few, so that store is uncapped.
+const sourcesStore = createJsonStore('sources.json', isValidSource, Infinity)
+const itemsStore = createJsonStore('media-items.json', isValidMediaItem, MAX_ITEMS)
 
 // --- Sources ----------------------------------------------------------------
 
 export function listSources(): Source[] {
-  return readJsonArray(sourcesFile(), isValidSource)
+  return sourcesStore.read()
 }
 
 export function getSource(id: string): Source | undefined {
@@ -62,31 +41,25 @@ export function getSource(id: string): Source | undefined {
 
 /** Insert or replace a source by id (a re-index updates the existing record). */
 export function upsertSource(source: Source): Source[] {
-  const sources = [source, ...listSources().filter((s) => s.id !== source.id)]
-  writeJson(sourcesFile(), sources)
-  return sources
+  return sourcesStore.write([source, ...listSources().filter((s) => s.id !== source.id)])
 }
 
 /** Toggle whether a source is watched for new uploads (Phase J). Returns all sources. */
 export function setSourceWatched(id: string, watched: boolean): Source[] {
-  const sources = listSources().map((s) => (s.id === id ? { ...s, watched } : s))
-  writeJson(sourcesFile(), sources)
-  return sources
+  return sourcesStore.write(listSources().map((s) => (s.id === id ? { ...s, watched } : s)))
 }
 
 /** Remove a source and all of its media items. Returns the remaining sources. */
 export function removeSource(id: string): Source[] {
-  const sources = listSources().filter((s) => s.id !== id)
-  writeJson(sourcesFile(), sources)
-  const items = listAllItems().filter((m) => m.sourceId !== id)
-  writeJson(itemsFile(), items)
+  const sources = sourcesStore.write(listSources().filter((s) => s.id !== id))
+  itemsStore.write(listAllItems().filter((m) => m.sourceId !== id))
   return sources
 }
 
 // --- Media items ------------------------------------------------------------
 
 function listAllItems(): MediaItem[] {
-  return readJsonArray(itemsFile(), isValidMediaItem)
+  return itemsStore.read()
 }
 
 export function listMediaItems(sourceId: string): MediaItem[] {
@@ -100,7 +73,7 @@ export function listMediaItems(sourceId: string): MediaItem[] {
  */
 export function replaceMediaItems(sourceId: string, items: MediaItem[]): void {
   const others = listAllItems().filter((m) => m.sourceId !== sourceId)
-  writeJson(itemsFile(), [...items, ...others].slice(0, MAX_ITEMS))
+  itemsStore.write([...items, ...others])
 }
 
 /**
@@ -130,6 +103,6 @@ export function setMediaItemDownloaded(id: string, filePath?: string): MediaItem
   const updated = all.map((m) =>
     m.id === id ? { ...m, downloaded: true, downloadedAt: Date.now(), filePath } : m
   )
-  writeJson(itemsFile(), updated)
+  itemsStore.write(updated)
   return updated.filter((m) => m.sourceId === target.sourceId)
 }