feat(audio-player): progress bar overhaul — ticks, buffer, wheel, tooltip, precision rail (plan §1)

The scrubber becomes a layered bar: the native <input type=range> stays
on top for a11y (focus, arrow keys, aria — its track goes transparent
via static page CSS) while the layers beneath render the state:

- Chapter ticks: density-decimated (denseTicks keeps only marks >= 4px
  apart) so an 1189-chapter 86-hour book gets ~100 readable marks
  instead of a solid mass; the current chapter's tick is tinted.
- Buffered span: the ACTIVE track's buffered-ahead end mapped into the
  global bar (buffers are per-track and never span the whole bar).
  bufferedAheadEnd reads the range containing the playhead — a huge
  m4b's moov index at the file tail is its own buffered range and must
  not read as 'the whole book is buffered'. Rides progress + the
  events that demonstrably fire for Range-served files that go
  network-idle while paused (timeupdate/canplay/loadedmetadata/playing).
- Wheel over the bar: ±5s nudge, Shift = ±60s.
- Hover tooltip: time + chapter title under the pointer.
- Precision rail: while dragging, a ±5-minute window floats below the
  bar (fixed anchor; release and re-grab to travel far) and the drag
  maps at minutes-per-pixel instead of hours-per-pixel — the whole
  point for 80h+ books. Click snaps to a chapter line within ~5s
  (snapToChapter).

Pointer handling is ours end-to-end: pointerdown maps hours-per-pixel
+ snaps, captured moves remap through the rail, release seeks. The
native drag default is prevented so the two mappings never fight;
keyboard arrows keep their native step and seek via change.

Time labels get reserved width — the bar no longer resizes when the
elapsed label grows from 0:00 to 43:07 mid-drag (caught by the rail
drag check measuring a 25% mapping drift).

Pure math in audio-scrubber.ts: pointer mapping, chapter lookup, snap,
tick density, per-track buffer→global span, rail window/mapping/ticks.
Unit: 16 new tests including both book shapes (86h/1189ch and
26h/34ch). Live: 23 Playwright checks on KJV (folder) and Gardens of
the Moon (single-file m4b); zip books share the folder manifest shape
(no zip fixture exists in the dev library). Probe user deleted.

web/src/audio.ts

@@ -28,6 +28,17 @@ import {
   type SleepChoice,
   type SleepState,
 } from "./audio-sleep";
+import {
+  bufferedAheadEnd,
+  bufferedSpanPct,
+  chapterIndexFor,
+  denseTicks,
+  railSecondsAtPointer,
+  railTicks,
+  railWindow,
+  secondsAtPointer,
+  snapToChapter,
+} from "./audio-scrubber";
 
 type AudioChapter = { index: number; title: string; start: number; end: number };
 
@@ -149,6 +160,17 @@ Alpine.data("audioReader", () => ({
   scrubbing: false,
   scrubValue: 0,
 
+  // Progress-bar overhaul (plan §1): chapter ticks, per-track buffer
+  // span, hover tooltip and the precision rail. Math lives in
+  // audio-scrubber.ts (pure, unit-tested).
+  tickIndices: [] as number[],
+  bufferedGlobal: null as number | null,
+  hoverSeconds: null as number | null,
+  hoverPct: 0,
+  railFrom: 0,
+  railTo: 0,
+  railTickList: [] as Array<{ start: number; title: string }>,
+
   // Track manifest: one AudioTrack per playable file. Single-file books
   // (m4b/mp3) carry exactly one track whose URL is the whole file, so
   // every code path below can treat playback as (track, local seconds)
@@ -331,9 +353,24 @@ Alpine.data("audioReader", () => ({
       this.updateMediaSessionState();
     });
     window.addEventListener("pagehide", () => this.pushProgress(true));
+    window.addEventListener("resize", () => this.recomputeTicks());
     document.addEventListener("visibilitychange", () => {
       if (document.visibilityState === "hidden") this.pushProgress(true);
     });
+    // Buffer readout for the scrubber's per-track buffer span.
+    // 'progress' alone does not fire reliably for Range-served files
+    // that go network-idle while paused — ride the events that
+    // demonstrably do, and re-read the (idempotent) ranges on each.
+    for (const ev of [
+      "progress",
+      "loadedmetadata",
+      "loadeddata",
+      "canplay",
+      "playing",
+      "timeupdate",
+    ]) {
+      audio.addEventListener(ev, () => this.updateBuffered());
+    }
 
     // Keyboard shortcuts (plan §2): one dispatcher resolving through
     // the declarative audio-keys.ts keymap. Hardware media keys ride
@@ -381,6 +418,8 @@ Alpine.data("audioReader", () => ({
     if (!audio || index < 0 || index >= this.tracks.length) return;
     const track = this.tracks[index];
     this.activeTrack = index;
+    this.bufferedGlobal = null; // buffers are per-track; the next
+    // 'progress' event re-reads the freshly loading element's ranges.
     if (audio.getAttribute("src") === track.url) {
       this.pendingSeek = null;
       audio.currentTime = Math.max(0, localSeconds);
@@ -404,6 +443,7 @@ Alpine.data("audioReader", () => ({
         this.chapters = (data.chapters || []) as AudioChapter[];
         this.bookDuration = data.duration_seconds || this.chapterEndEstimate();
         this.buildTracks(data);
+        this.recomputeTicks();
         const audio = this.audio();
         if (audio && !audio.getAttribute("src") && this.tracks[0]) {
           audio.setAttribute("src", this.tracks[0].url);
@@ -609,6 +649,128 @@ Alpine.data("audioReader", () => ({
     return Number.isFinite(n) ? n : 0;
   },
 
+  // ---- progress bar (audio-scrubber.ts math) ----
+
+  recomputeTicks() {
+    const area = document.getElementById("scrub-area");
+    const width = area ? area.getBoundingClientRect().width : 0;
+    this.tickIndices = denseTicks(
+      this.chapters,
+      this.chaptersDuration() || this.bookDuration || 1,
+      width,
+    );
+  },
+
+  updateBuffered() {
+    const audio = this.audio();
+    if (!audio || audio.buffered.length === 0) {
+      this.bufferedGlobal = null;
+      return;
+    }
+    // Buffered-ahead of the playhead (element-local): the end of the
+    // range containing currentTime. The moov-index range at a huge
+    // m4b's tail must not read as "the whole book is buffered".
+    const ranges = Array.from({ length: audio.buffered.length }, (_, i) => ({
+      start: audio.buffered.start(i),
+      end: audio.buffered.end(i),
+    }));
+    this.bufferedGlobal = bufferedAheadEnd(ranges, audio.currentTime);
+  },
+
+  chapterTitleAt(seconds: number): string {
+    const idx = chapterIndexFor(this.chapters, seconds);
+    if (idx === -1) return this.title;
+    const ch = this.chapters[idx];
+    return ch.title || `Chapter ${idx + 1}`;
+  },
+
+  scrubFillPct(): number {
+    const value = this.scrubbing ? this.scrubValue : Number(this.currentTime);
+    return Math.min(100, Math.max(0, (value / (this.chaptersDuration() || 1)) * 100));
+  },
+
+  bufferSpan(): { left: number; width: number } | null {
+    return bufferedSpanPct(
+      this.tracks[this.activeTrack],
+      this.bufferedGlobal,
+      this.chaptersDuration() || 1,
+    );
+  },
+
+  railMarkerPct(): number {
+    const span = Math.max(1, this.railTo - this.railFrom);
+    return Math.min(100, Math.max(0, ((this.scrubValue - this.railFrom) / span) * 100));
+  },
+
+  // Click/drag on the bar: the FIRST press maps hours-per-pixel and
+  // snaps to a chapter line within ~5s; while held, the precision rail
+  // takes over at minutes-per-pixel (re-grab to travel far). The
+  // native range stays underneath for keyboard/aria — its drag default
+  // is prevented so the two mappings never fight.
+  scrubPointerDown(e: PointerEvent) {
+    if (e.button !== 0) return;
+    e.preventDefault();
+    const area = e.currentTarget as HTMLElement;
+    const rect = area.getBoundingClientRect();
+    try {
+      area.setPointerCapture(e.pointerId);
+    } catch {
+      /* synthetic or already-released pointer — drag still works via
+         the element-level listeners */
+    }
+    document.getElementById("audio-scrub")?.focus({ preventScroll: true });
+    const duration = this.chaptersDuration() || 1;
+    const at = snapToChapter(secondsAtPointer(e.clientX, rect, duration), this.chapters, 5).seconds;
+    this.scrubbing = true;
+    this.scrubValue = at;
+    const window = railWindow(at, duration);
+    this.railFrom = window.from;
+    this.railTo = window.to;
+    this.railTickList = railTicks(window, this.chapters);
+  },
+
+  scrubPointerMove(e: PointerEvent) {
+    const area = e.currentTarget as HTMLElement;
+    const rect = area.getBoundingClientRect();
+    const duration = this.chaptersDuration() || 1;
+    if (!this.scrubbing) {
+      this.hoverSeconds = secondsAtPointer(e.clientX, rect, duration);
+      this.hoverPct =
+        rect.width > 0
+          ? Math.min(100, Math.max(0, ((e.clientX - rect.left) / rect.width) * 100))
+          : 0;
+      return;
+    }
+    this.scrubValue = railSecondsAtPointer(e.clientX, rect, {
+      from: this.railFrom,
+      to: this.railTo,
+    });
+  },
+
+  scrubPointerLeave() {
+    if (!this.scrubbing) this.hoverSeconds = null;
+  },
+
+  scrubPointerUp(e: PointerEvent) {
+    if (!this.scrubbing) return;
+    const area = e.currentTarget as HTMLElement;
+    if (area.hasPointerCapture && area.hasPointerCapture(e.pointerId))
+      area.releasePointerCapture(e.pointerId);
+    this.seekTo(this.scrubValue);
+    this.scrubbing = false;
+    this.hoverSeconds = null;
+  },
+
+  // Wheel over the bar: ±5s nudge, Shift = ±60s. Scroll up = forward.
+  onScrubWheel(e: WheelEvent) {
+    e.preventDefault();
+    const step = e.shiftKey ? 60 : 5;
+    const direction = e.deltaY > 0 ? -1 : 1;
+    const duration = this.chaptersDuration() || 1;
+    const target = Math.min(duration, Math.max(0, this.globalPosition() + direction * step));
+    this.seekTo(target);
+  },
+
   toggleBookmarkCapture() {
     if (this.bookmarkCaptureOpen) {
       this.bookmarkCaptureOpen = false;