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>

ROADMAP.md

@@ -84,24 +84,72 @@ smoke test.*
       The archive file lives at a fixed `userData/download-archive.txt`
       (`getDownloadArchivePath()` in `src/main/settings.ts`), not user-configurable.
 
-## Phase C — Custom commands & yt-dlp management
+## Phase C — Custom commands & yt-dlp management ✅ COMPLETE
 
-- [ ] **Custom command templates.** Named, editable templates of extra yt-dlp args; pick a
-      default; a "run custom command" mode. Needs persistence + a template editor view.
-- [ ] **Command preview.** Show the exact yt-dlp command line before running (build the argv
-      and render it).
-- [ ] **In-app yt-dlp updater** with stable/nightly channel (`--update-to`, or fetch the
-      release exe), surfaced next to the existing version check.
+Named `CommandTemplate`s (`src/shared/ipc.ts`) persist to `templates.json`
+(`src/main/templates.ts`, mirrors `history.ts`'s plain-JSON pattern) and are managed
+inline in **Settings → Custom commands** via `TemplateManager.tsx` — no modal, matching
+the rest of the app's no-portal-overlay convention (see the Hint/Select comments re:
+this dev machine's GPU/driver). A template's extra yt-dlp flags are shell-split
+(`parseExtraArgs`, `src/main/buildArgs.ts`) and appended to the generated argv
+immediately before the `--` URL terminator, so a template flag can override anything
+chosen earlier. `Settings.customCommandEnabled` + `defaultTemplateId` apply a template
+to every new download; the download bar's own **Custom command** panel lets a single
+download override that default or opt out entirely (`extraArgs` on
+`StartDownloadOptions`, mirroring the existing per-download `options` override).
+`buildCommand()` (`src/main/download.ts`) now centralises settings/access/
+options/extraArgs resolution, shared by both the real `startDownload` spawn and the new
+preview path. All items verified in the UI preview + `npm run typecheck` +
+`npm run test` (11 new unit tests covering `parseExtraArgs`, `formatCommandLine`, and
+extraArgs ordering). *Caveat: the extra-args splitting and command construction were
+validated by reasoning + tests, not yet by a real yt-dlp run with actual custom flags —
+worth a real-download smoke test pass, same as Phase A/B.*
 
-## Phase D — Library, UX & notifications
+- [x] **Custom command templates.** Named, editable templates of extra yt-dlp args
+      (`CommandTemplate`), CRUD'd inline via `TemplateManager.tsx`; persisted to
+      `templates.json`. **Pick a default** via `Settings.defaultTemplateId` (a Select in
+      the Custom commands card). The **"run custom command" mode** is
+      `Settings.customCommandEnabled`, applied to every new download unless overridden
+      per-download in the download bar's Custom command panel.
+- [x] **Command preview.** `IpcChannels.commandPreview` → `previewCommand()`
+      (`src/main/download.ts`) builds the exact argv via the same `buildCommand()` path
+      a real download would take, then renders it with `formatCommandLine`. Surfaced as
+      a **Preview command** button in the download bar, with a Copy button.
+- [x] **In-app yt-dlp updater.** `updateYtdlp(channel)` (`src/main/ytdlp.ts`) runs
+      yt-dlp's own `--update-to stable|nightly`. Surfaced in **Settings → About**, right
+      next to the existing version check, with a channel picker + result output.
 
-- [ ] **History search + multi-select + filter** (video/audio) + bulk delete + **re-download**.
-      Schema already exists in `src/shared/ipc.ts`; needs UI + likely the planned move to
-      better-sqlite3.
-- [ ] **Native OS notifications** on completion / failure (Electron `Notification`).
-- [ ] **Private / incognito mode** — a download that skips history.
-- [ ] **Backup / restore** settings + templates (export / import JSON).
-- [ ] **Error log / copy error report** view (Seal's debug report).
+## Phase D — Library, UX & notifications ✅ COMPLETE
+
+History stays plain JSON (`history.json`, 500-entry cap) — search/filter/select are done
+client-side over the already-small array, so the planned better-sqlite3 migration wasn't
+needed for this phase and was deliberately skipped to avoid a native-module build step for
+no functional gain at this scale. Failed downloads (pre-spawn rejections and in-flight
+yt-dlp failures alike) now persist to a new `errorlog.json` (`src/main/errorlog.ts`,
+200-entry cap) independent of the queue, so a report survives `Clear finished`. Native
+notifications and the backup file both reuse existing settings/templates plumbing
+(`getSettings`/`setSettings`, `listTemplates`/the new `replaceTemplates`) rather than adding
+parallel storage. All items verified in the UI preview (typecheck + `npm run test` clean).
+
+- [x] **History search + multi-select + filter** (video/audio) + bulk delete + **re-download**.
+      `HistoryView.tsx` gained a search box, an All/Video/Audio filter, a "Select" mode with
+      per-row checkboxes + select-all + **Delete selected** (new `historyRemoveMany` IPC,
+      `src/main/history.ts`), and a per-row re-download button that re-queues the entry's
+      URL/kind/quality via the existing `addFromUrl`.
+- [x] **Native OS notifications** on completion / failure (Electron `Notification`,
+      `src/main/download.ts`). Gated by a new **Notify when downloads finish** switch
+      (`Settings.notifyOnComplete`, default on); clicking a notification refocuses the window.
+- [x] **Private / incognito mode** — a download bar toggle (`DownloadBar.tsx`, sticky like an
+      incognito tab) sets `DownloadItem.incognito`, which `store/downloads.ts` checks before
+      ever calling `useHistory().add(...)`. Queue items show an eye-off badge when private.
+- [x] **Backup / restore** settings + templates (export / import JSON). New
+      `src/main/backup.ts` writes/reads `{ settings, templates }` via a save/open dialog;
+      `replaceTemplates()` (`src/main/templates.ts`) does a full restore rather than a
+      merge-by-id. Surfaced as **Settings → Backup & restore**.
+- [x] **Error log / copy error report** view (Seal's debug report). New
+      `src/main/errorlog.ts` persists every failure (pre-spawn rejection, spawn error, or
+      non-zero yt-dlp exit); **Settings → Diagnostics** lists recent entries with
+      **Copy full report** and **Clear log**.
 
 ## Phase E — Theming & platform polish