feat: queue UX (Phase M) + media editing (split-chapters, trim)

Phase L (media editing):
- Split by chapters (--split-chapters) as a DownloadOptions toggle
- Trim/cut by time range: parseTrimSections -> --download-sections "*A-B"
  + --force-keyframes-at-cuts (deduped vs SponsorBlock), per-download Trim panel

Phase M (queue & daily-use UX), all 7:
- Pause/resume: main-side killTree + paused flag (silent close), download:pause
  IPC, store pause/resume + paused status, QueueItem controls
- Reorder via "Download next" (prioritize)
- Aggregate progress strip (pure summarizeQueue) + combined speed/ETA
- Drag-and-drop links / .url files onto the download card
- Retry all failed
- Duplicate detection (sameVideo) with "Download anyway" guard
- Per-download scheduling (datetime-local) + save-for-later (saved status,
  15s promotion ticker); session-only (queue not persisted)

New pure modules unit-tested (queueStats); buildArgs trim/split tested.
typecheck + test green (178 passed). Roadmap updated: Phase M COMPLETE.

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

ROADMAP.md

@@ -166,7 +166,7 @@ parallel storage. All items verified in the UI preview (typecheck + `npm run tes
       non-zero yt-dlp exit); **Settings → Diagnostics** lists recent entries with
       **Copy full report** and **Clear log**.
 
-## Phase E — Theming & platform polish
+## Phase E — Theming & platform polish ✅ COMPLETE
 
 Some items are Android-specific in Seal and adapted to Windows here.
 
@@ -187,10 +187,6 @@ Some items are Android-specific in Seal and adapted to Windows here.
       auto. Verified in the UI preview (typecheck + `npm run test` clean): default Toffee,
       switching to Slate/Evergreen/Lavender, Light/Dark/Follow-system, and the sidebar
       toggle's break-out-of-system behavior all checked visually.
-- [ ] **i18n / language setting** (Seal ships ~40 languages). Large but optional — deferred,
-      since shipping ~40 real translations isn't something to fake; doing this properly means
-      wiring up an i18n library + extracting every string now, with translation content
-      arriving incrementally from contributors.
 - [x] **Windows "open with" / share integration.** Both mechanisms named above, since a Win32
       (non-MSIX) app can't register as an actual Share Target:
       - **`aerofetch://` protocol** (`aerofetch://download?url=<encoded>`) — registered at
@@ -274,49 +270,77 @@ YTDLnis's signature differentiator. The keyframe plumbing already exists in Aero
 (`--force-keyframes-at-cuts` is emitted today for SponsorBlock-remove in
 `src/main/buildArgs.ts`), so this is cheaper than it looks.
 
-- [ ] **Trim / cut downloads.** Download only part of a video, or remove segments — by
-      **timestamp** or by **chapter**, with multiple cuts allowed. → yt-dlp
-      `--download-sections "*START-END"` (repeatable) + `--force-keyframes-at-cuts`.
-      Chapters come free from the probe's `yt-dlp -J` `chapters[]` array (`src/main/probe.ts`).
-      New fields on `DownloadOptions` (or a per-download override), surfaced as a **Trim**
-      panel in `src/renderer/src/components/DownloadBar.tsx`. *v1 can skip a scrubber/preview
-      player — timestamp inputs + checkboxes of the probed chapter list is enough. Smoke-test
-      the exact multi-section output behaviour (one file vs. per-section) the same way
-      Phases A–C smoke-tested live yt-dlp.*
-- [ ] **Split by chapters into separate files.** → `--split-chapters` (already flagged as a
+- [x] **Trim / cut downloads.** Keep only chosen time ranges (multiple allowed). →
+      `parseTrimSections` (`src/main/buildArgs.ts`) normalises raw user text into yt-dlp
+      `--download-sections "*START-END"` specs (+ `--force-keyframes-at-cuts`, deduped against
+      SponsorBlock-remove). Threaded as `StartDownloadOptions.trim` through
+      `store/downloads.ts`, surfaced as a collapsible **Trim** panel in `DownloadBar.tsx`
+      (single downloads only). *Implemented + unit-tested (`buildArgs.test.ts` — 7 new tests;
+      typecheck + test green). Live smoke test pending, plus two follow-ups: timestamp-range
+      only so far (chapter-based cuts via the probe `chapters[]` array, and a scrubber/preview
+      player, still TODO).*
+- [x] **Split by chapters into separate files.** → `--split-chapters` (already flagged as a
       TODO in Phase A above). One toggle on `DownloadOptions` +
-      `src/renderer/src/components/DownloadOptionsForm.tsx`; pairs naturally with trim. Uses an
-      `--output chapter:` template for the per-chapter filenames.
+      `src/renderer/src/components/DownloadOptionsForm.tsx`; pairs naturally with trim. yt-dlp
+      keeps the full file and writes per-chapter files via its default `chapter:` template.
+      *Implemented + unit-tested (`buildArgs.test.ts`, typecheck + test green); live smoke test
+      still pending.*
 - [ ] **Metadata editing before download.** Change title / author / artist pre-download
       (YTDLnis: "modify metadata such as title and author"). → `--parse-metadata` /
-      `--ppa "Metadata:-metadata title=…"`; fits the audio path of `DownloadOptions`. Good for
-      building a clean music library where the source title is messy.
+      `--replace-in-metadata`; fits the audio path. Good for building a clean music library
+      where the source title is messy. *Held: the exact set-a-literal recipe is fragile
+      (`--parse-metadata FROM:TO` splits on a colon that titles often contain;
+      `--replace-in-metadata FIELD REGEX REPLACE` has empty-field + regex-replacement edge
+      cases) — confirm against a live yt-dlp run before wiring it, rather than guessing the
+      flag.*
 
-## Phase M — Queue & daily-use UX
+## Phase M — Queue & daily-use UX ✅ COMPLETE
 
 Neither Seal nor Pinchflat covers these; they're what makes the queue pleasant to live in.
 Today `src/renderer/src/store/downloads.ts` has cancel + retry only.
 
-- [ ] **Pause / resume individual downloads.** → yt-dlp resumes `.part` files via `--continue`
-      (already the default). Pause = kill the child (existing `taskkill /pid /T /F` path) but
-      keep the partial + mark the item `paused`; resume = relaunch the same item, which
-      continues. New `paused` state in the queue store.
-- [ ] **Reorder / prioritize the queue.** Drag a queued item up. The renderer scheduler
-      (`pump()` promotes oldest-queued-first) already treats the queued array as the order, so
-      this is reordering that array.
-- [ ] **Aggregate progress + total ETA + combined speed.** A header strip on the Downloads
+- [x] **Pause / resume individual downloads.** → yt-dlp resumes `.part` files via `--continue`
+      (already the default). *Done: `pauseDownload()` (`src/main/download.ts`) reuses the
+      `taskkill /T /F` tree-kill via a new `killTree` helper but flags the record `paused` so
+      the close/error handlers stay silent (no error event/log/notification); new
+      `download:pause` IPC + preload bridge. Renderer `pause`/`resume` (`store/downloads.ts`) +
+      a `paused` status: pause frees a concurrency slot, resume re-queues WITHOUT resetting
+      progress so the relaunch continues the partial. Pause/Resume buttons + a frozen progress
+      row in `QueueItem.tsx`; paused items survive "Clear finished". typecheck + test green;
+      live resume-continues-the-.part still wants a smoke test.*
+- [x] **Reorder / prioritize the queue.** *Done as a **"Download next"** action rather than
+      drag: since the queue renders newest-first while `pump()` promotes oldest-first, a
+      reposition primitive is clearer than drag. `prioritize(id)` (`store/downloads.ts`) moves a
+      queued item to the front of the promotion order; an up-arrow button on queued rows
+      (`QueueItem.tsx`).*
+- [x] **Aggregate progress + total ETA + combined speed.** A header strip on the Downloads
       view summing bytes/speed across active items. Feeds straight into Phase O's taskbar
-      progress bar.
-- [ ] **Drag-and-drop a link or `.url` file onto the window.** A window `drop` handler that
-      accepts `text/uri-list` and Internet-Shortcut files, reusing `extractIncomingUrl()`
-      from `src/main/deeplink.ts` (already validates http(s)-only).
-- [ ] **Retry all failed.** One action that re-enqueues every entry in `src/main/errorlog.ts`.
-- [ ] **Duplicate detection.** Warn ("you already have this") when a URL/video-id is already in
-      history or the active queue before enqueuing.
-- [ ] **Per-download scheduling + "save for later."** YTDLnis lets you "schedule by date and
-      time" and park items. Add `scheduledFor?: number` + a `saved` state to `DownloadItem`;
-      `pump()` gains a time gate before promotion. Distinct from the existing background
-      `--sync` schedule (Phase J), which is for *sources*, not one-off items.
+      progress bar. *Done: pure `summarizeQueue` (`store/queueStats.ts`) → a strip in
+      `DownloadsView.tsx` (overall %, combined speed, longest-ETA "time left"); unit-tested
+      (`test/queueStats.test.ts`). A true remaining-bytes combined ETA is still out of reach —
+      we don't track per-item sizes — so "time left" is the longest single ETA.*
+- [x] **Drag-and-drop a link or `.url` file onto the window.** *Done: the download card
+      (`DownloadBar.tsx`) handles `onDragOver`/`onDrop` with a dashed-outline drag highlight,
+      accepting `text/uri-list`/`text/plain` (`firstUrl`) and dropped Windows `.url`
+      Internet-Shortcut files (`parseUrlFile`, read via `File.text()`); both http(s)-validated by
+      the existing `looksLikeUrl`. A dropped link fills the URL field.*
+- [x] **Retry all failed.** One action that re-enqueues every failed item. *Done:
+      `retryAll()` in `store/downloads.ts` re-queues all `error` items + a "Retry all failed (N)"
+      button in `DownloadsView.tsx`. (Re-queues live queue items rather than reading
+      `errorlog.json` — same effect for the on-screen failures.)*
+- [x] **Duplicate detection.** Warn ("you already have this") before enqueuing a URL already in
+      the active queue. *Done: pure `sameVideo()` (`store/queueStats.ts`, YouTube-id aware +
+      normalised-URL fallback) drives a "Already in your queue — Download anyway?" banner in
+      `DownloadBar.tsx`; unit-tested. Checks the live queue (which still holds recently-completed
+      items); cross-checking `history.json` for older downloads is a possible extension.*
+- [x] **Per-download scheduling + "save for later."** *Done: a `saved` status + optional
+      `scheduledFor` (`store/downloads.ts`); `pump()` ignores `saved` (the time gate), and a 15s
+      ticker promotes due scheduled items to `queued`. UI: a **Schedule** panel with a native
+      `datetime-local` input in `DownloadBar.tsx` (future time parks the new download as
+      scheduled), plus per-row **Save for later** / **Add to queue** actions in `QueueItem.tsx`;
+      saved items survive "Clear finished". Distinct from the Phase J `--sync` schedule (which is
+      for *sources*). **Limitation: the queue isn't persisted, so a schedule only fires while
+      AeroFetch is running** — noted in the UI hint and the code.*
 
 ## Phase N — Power-user surface