Complete Phase C (custom commands & yt-dlp updater) and Phase D (library, UX & notifications)

Phase C had been implemented in the working tree but never committed:
named custom-command templates (CRUD + per-download override), command
preview, and the in-app yt-dlp self-updater.

Phase D adds: history search/kind-filter/multi-select/bulk-delete/
re-download; native OS notifications on completion/failure; a private/
incognito download mode that skips history; settings+template backup/
restore via JSON; and a persistent error log surfaced as a Diagnostics
report in Settings.

See ROADMAP.md for the full per-item breakdown.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/shared/ipc.ts

@@ -18,12 +18,22 @@ export const IpcChannels = {
   historyList: 'history:list',
   historyAdd: 'history:add',
   historyRemove: 'history:remove',
+  historyRemoveMany: 'history:remove-many',
   historyClear: 'history:clear',
   /** main → renderer push channel for live download events */
   downloadEvent: 'download:event',
   cookiesLogin: 'cookies:login',
   cookiesStatus: 'cookies:status',
-  cookiesClear: 'cookies:clear'
+  cookiesClear: 'cookies:clear',
+  templatesList: 'templates:list',
+  templatesSave: 'templates:save',
+  templatesRemove: 'templates:remove',
+  commandPreview: 'command:preview',
+  ytdlpUpdate: 'ytdlp:update',
+  errorLogList: 'errorlog:list',
+  errorLogClear: 'errorlog:clear',
+  backupExport: 'backup:export',
+  backupImport: 'backup:import'
 } as const
 
 /** Sentinel format id meaning "let yt-dlp pick the best video+audio". */
@@ -128,6 +138,16 @@ export interface YtdlpVersionResult {
   error?: string
 }
 
+/** yt-dlp's self-update release channel (`--update-to <channel>`). */
+export type YtdlpUpdateChannel = 'stable' | 'nightly'
+
+export interface YtdlpUpdateResult {
+  ok: boolean
+  /** yt-dlp's own update output, e.g. "Updated to ... " or "yt-dlp is up to date" */
+  output?: string
+  error?: string
+}
+
 /** A single selectable output format, derived from `yt-dlp -J`. */
 export interface FormatOption {
   /** yt-dlp format_id, or BEST_FORMAT_ID for the auto-best option */
@@ -198,6 +218,14 @@ export interface StartDownloadOptions {
   formatHasAudio?: boolean
   /** per-download post-processing override; main falls back to settings defaults */
   options?: DownloadOptions
+  /**
+   * Per-download custom-command override: raw extra yt-dlp flags appended to
+   * the generated argv (see CommandTemplate). Omit to fall back to the
+   * persisted settings default (customCommandEnabled + defaultTemplateId);
+   * pass an empty string to explicitly run with no extra args for just this
+   * download even when the settings default is enabled.
+   */
+  extraArgs?: string
 }
 
 export interface StartDownloadResult {
@@ -262,6 +290,32 @@ export interface Settings {
   restrictFilenames: boolean
   /** record completed downloads in a yt-dlp --download-archive file to skip repeats */
   downloadArchive: boolean
+  /** apply a named custom-command template's extra args to every new download */
+  customCommandEnabled: boolean
+  /** id of the CommandTemplate applied when customCommandEnabled is on; null = none picked yet */
+  defaultTemplateId: string | null
+  /** show a native OS notification when a download finishes or fails */
+  notifyOnComplete: boolean
+}
+
+/**
+ * A named, reusable set of extra yt-dlp CLI flags (Phase C "custom commands"),
+ * e.g. name: 'Write thumbnail + no mtime', args: '--write-thumbnail --no-mtime'.
+ * Shell-split (see parseExtraArgs) and appended to the generated argv just
+ * before the `--` URL terminator, so they can override earlier flags.
+ */
+export interface CommandTemplate {
+  id: string
+  name: string
+  args: string
+}
+
+/** Result of building the exact yt-dlp command line for the current form state, without running it. */
+export interface CommandPreviewResult {
+  ok: boolean
+  /** full command line (binary + quoted args), for display/copy only */
+  command?: string
+  error?: string
 }
 
 /** Whether the built-in sign-in window has ever saved a cookie file, and when. */
@@ -293,3 +347,33 @@ export interface HistoryEntry {
   /** epoch milliseconds */
   completedAt: number
 }
+
+/**
+ * A failed download or download-start attempt, persisted to errorlog.json
+ * (newest-first) so the report survives the queue item being cleared —
+ * Seal's "debug report" equivalent.
+ */
+export interface ErrorLogEntry {
+  id: string
+  /** resolved video title when known; falls back to the URL in the UI */
+  title?: string
+  url: string
+  kind: MediaKind
+  error: string
+  /** epoch milliseconds */
+  occurredAt: number
+}
+
+/** Result of exporting settings + custom-command templates to a JSON file. */
+export interface BackupExportResult {
+  ok: boolean
+  /** absolute path written to, present when ok is true */
+  path?: string
+  error?: string
+}
+
+/** Result of restoring settings + custom-command templates from a JSON file. */
+export interface BackupImportResult {
+  ok: boolean
+  error?: string
+}