fix(scripts): refuse to start dev-headless on a port somebody else holds

dev-headless.sh checked the PID in *this* worktree's .dev/app.pid and
nothing else, so an app orphaned by a deleted worktree went on listening
with nothing left to stop it — `make dev-stop` only kills the pid it
wrote. The new app then started, failed to bind, exited, and every
subsequent curl and playwright-cli call went to the other process: the
harness reported facts about an app nobody asked for.

That fails a long way from its cause. It presented as "no such table:
libraries" against a *freshly created* YJ_HOME, which reads exactly like
applySchema or staleshape.go having gone wrong, with a zero-byte app.log
beside it saying nothing.

The startup wait cannot catch this, because its health check is satisfied
by any app on the port — which is precisely the failure — so the check is
before the launch and refuses rather than warns. It names the holder's
pid, cmdline and /proc/<pid>/cwd, which is what identifies the checkout
and says "(deleted)" for the case this exists for. It does not suggest
`make dev-stop`: the PID-file check has already passed, so by
construction dev-stop does not know about this process and would report
success while changing nothing. --port already covers the legitimate
second-app case.

The second, cheaper guard the report asks for goes in after the wait:
"the port answered" is not "the app we started answered", so a dead
APP_PID at that point is now an error with the log tail rather than a
success message about somebody else's process.

Closes #119

.planning/NOTES.md

@@ -3580,3 +3580,87 @@ per-card flag can answer at all.
 The general point: **two columns that agree today are not one column.**
 Which of them a new surface reads should be decided by which one has
 something that can un-set it.
+
+## The queue panel was a column that could not afford to be one (measured 2026-08-19)
+
+Plan 018, issue #24. Measured against the running app (`make
+dev-headless SEED=default`, Chromium) on Playlists, sweeping the
+viewport with the queue open and closed. Main panel width, and how much
+of the page header survived:
+
+| viewport | sidebar | main (queue open) | actions clipped |
+|---|---|---|---|
+| 1280×800 | 200 | 759 | — |
+| 1000×700 | 200 | 479 | 2 of 3 |
+| **900×600** | 200 | **379** | all three |
+| 800×600 | 56 | 423 | all three |
+| 390×780 | — | **69** | all three |
+| 320×600 | — | **0** | all three |
+| 800×600 | 56 | 744 *(closed)* | New Smart Playlist, 158/162px |
+
+Five things came out of it that the issue did not say.
+
+- **The header clips at the enforced minimum with the queue closed.**
+  800×600 is the only size this app promises, and "New Smart Playlist"
+  loses 4px of its 162 there. The queue makes it dramatic; it is not
+  the cause.
+- **900×600 is worse than 800×600.** `AUTO_COLLAPSE_VIEWPORT` collapses
+  the sidebar *below* 900, so the main panel is 843px at 899 and 700px
+  at 900. **The worst desktop case is the top of the Compact band, not
+  the enforced floor** — so every viewport list that stopped at "the
+  minimum" was missing its own worst case. `layout-overflow.spec.ts`
+  carries 900 now.
+- **At 320px the main panel was 0px.** The panel is `flex-shrink: 0` in
+  the flow of `.content-area`, so an open queue is paid for by the
+  content rather than covering it. Not degraded — gone. That is the
+  measurement #55 wanted and did not have.
+- **Only Playlists overflows.** All ten primary views swept at 900×600
+  and 390×780; every other header reports `scrollWidth ==
+  clientWidth`, and Albums at 390 renders title, count and sort legibly
+  (checked on a screenshot, not just the number). So #69 is one view's
+  action set — three text buttons totalling 390px — and not a systemic
+  header failure.
+- **Both reasons in `MinWidth`'s comment had expired.** The subtitle is
+  `display: none` from 899 down, and the sidebar host is
+  `overflow-y: auto` (at 600×460, `scrollHeight` 434 against a 332px
+  client, Settings reachable after scrolling). The floor is right; its
+  stated defence was two mechanisms that can no longer happen, which is
+  worse than either answer because nobody can argue with it.
+
+**A correction worth keeping, because it nearly went in the plan.** My
+first probe for the sidebar's scroller searched
+`shadowRoot.querySelectorAll('*')` and reported "no scroller — items
+are unreachable", which reads exactly like a live Settings-unreachable
+bug. The scroller is the **host**, and a host is not inside its own
+shadow root. CLAUDE.md was right and the probe was wrong.
+
+**And one claim in the plan's first draft was too strong**: that the
+overlay "removes the desktop half of #69". After phase 2, at 900×600,
+open and closed are now *identical* (main 700, one action clipped)
+where open used to be main 379 with all three clipped. The queue's
+contribution is gone; the header's own overflow remains and is still a
+live defect at a supported size.
+
+### The mode cannot be a media query
+
+The panel is drag-resizable 200–500px and persisted, so a viewport
+breakpoint assumes the default 320 and is wrong by up to 180px for a
+user who widened it — in the direction that hurts, since a wider queue
+is exactly when the content can least afford it. It is computed from
+`.content-area`'s width instead (which already accounts for the
+sidebar's collapse), and the component test that matters widens the
+panel at a *fixed* parent width and asserts the flip.
+
+The floor (480) is a judgement, and the measurement is why: there is no
+cliff. The track list rescales its columns continuously — 213px down to
+124px between main widths of 900 and 544, `rowOverflow=0` at every step
+— and the album grid steps 3 columns to 2 somewhere between 564 and 644
+without breaking. So 480 is anchored at both ends instead: it keeps the
+default 1100px window inline, and puts every measured-broken case on
+the overlay side.
+
+The scrim is perceptible but subtle on a dark ramp, which is worth
+knowing before someone "fixes" it as broken: sampled from screenshots at
+900×600, the main panel's background goes 33,37,41 → 18,20,23 and a
+row's text 242 → 133. It covers the content area only — not the sidebar
+or the transport — because the queue is not modal.

.planning/plans/active/018-supported-sizes-and-the-queue-model.md

@@ -0,0 +1,294 @@
+# 018 — Supported sizes, and what the queue panel is
+
+**Issue:** #24 (`Area/Shell-Nav`, `Priority/High`, `Reviewed/Confirmed`)
+**Unblocks:** #55 (queue as a screen) — a real Gitea dependency
+**Relates:** #69 (page-header overflow), #12 (mini-player), #51 (small-screen umbrella)
+**Status:** in flight
+
+#73 puts this first in Phase 2 and hangs the rest of the phase off it,
+so the decision has to be written down and arguable before any CSS
+moves. This document is the decision. Everything below the matrix is
+either a measurement or an argument for one of the four choices #24
+asks for.
+
+---
+
+## What is actually wrong, measured
+
+Against the running app (`make dev-headless SEED=default`, Chromium),
+Playlists, sweeping the viewport with the queue open and closed. The
+number that matters is how much of the page header survives.
+
+| viewport | sidebar | queue | main panel | header needs | actions clipped |
+|---|---|---|---|---|---|
+| 1280×800 | 200 | open 321 | 759 | 759 | — |
+| 1000×700 | 200 | open 321 | 479 | 747 | New Playlist, New Smart Playlist |
+| **900×600** | 200 | open 321 | **379** | 747 | **all three** |
+| 800×600 | 56 | open 321 | 423 | 747 | all three |
+| 700×600 | 56 | open 321 | 323 | 747 | all three |
+| 390×780 | — | open 321 | **69** | 747 | all three |
+| 320×600 | — | open 321 | **0** | 747 | all three |
+| 900×600 | 200 | closed | 700 | 747 | New Smart Playlist |
+| **800×600** | 56 | closed | 744 | 747 | **New Smart Playlist (158/162px)** |
+| 320×600 | — | closed | 320 | 747 | all three |
+
+Five things in that table are not in the issue.
+
+**The header clips at the supported minimum with the queue closed.**
+At 800×600 — the size `backend/config/window.go` enforces and the only
+size this app *promises* — "New Smart Playlist" loses 4px of its 162.
+#24 reads as a queue-panel bug; the queue makes it dramatic, but the
+header overflows on its own at the minimum window.
+
+**900×600 is worse than 800×600, because the sidebar expands at 900.**
+`AUTO_COLLAPSE_VIEWPORT` collapses the sidebar to icons *below* 900, so
+at 899px the main panel is 843px and at 900px it is 700px. The worst
+desktop case is therefore not the minimum window; it is the pixel
+immediately above the collapse. Anything that tests "the minimum" and
+stops has not tested the worst case, which is what
+`layout-overflow.spec.ts` does today.
+
+**At phone widths the queue is not a drawer, it is an amputation.**
+`queue-panel`'s host is `flex-shrink: 0; width: 0`, going to
+`width: var(--queue-width, 320px)` under `[open]` — it is *in the flow*
+of `.content-area`, so it takes its width from the main panel rather
+than covering it. At 390px that leaves 69px of the page; at 320px it
+leaves **0px**, and the app is not degraded but gone. This is the
+measurement #55 needs and did not have.
+
+**Only Playlists overflows.** Sweeping all ten primary views at 900×600
+and at 390×780, every other header reports `scrollWidth ==
+clientWidth`, and Albums at 390px renders title, count and sort
+legibly (checked on a screenshot, not just the number). #69 is
+therefore one view's action set — three text buttons totalling 390px —
+and not a systemic header failure, though the *rule* still belongs in
+`page-header`.
+
+**Both reasons in `MinWidth`'s comment are stale.** It says the floor is
+800×600 because "below ~780 the header's subtitle wraps" and "below
+~600 tall the eleven sidebar items no longer fit". The subtitle is
+`display: none` below 900 (index.css), and the sidebar host is
+`overflow-y: auto` — at 600×460 its `scrollHeight` is 434 against a
+332px client, and Settings is reachable after scrolling. Neither
+mechanism can happen any more. That does not mean the floor should
+move; it means its stated reason no longer supports it, which is worse
+than either answer.
+
+*(Care needed: my first probe for the sidebar scroller searched
+`shadowRoot.querySelectorAll('*')` and reported "items are
+unreachable", because the scroller is the **host** and a host is not in
+its own shadow root. The claim in CLAUDE.md is correct.)*
+
+---
+
+## Decision 1 — the supported size matrix
+
+Three bands. Two of them already exist and are already argued; what is
+new is that they are written down as a *promise*, and that the queue is
+part of it.
+
+| band | width | navigation | queue | promise |
+|---|---|---|---|---|
+| **Phone** | < 600 | `bottom-nav` + drawer | overlay, full width | reflows; nothing needs sideways scrolling; fits 320px |
+| **Compact** | 600 – 899 | icon sidebar | overlay + scrim | nothing is clipped or unreachable at any width in the band |
+| **Desktop** | ≥ 900 | labelled sidebar | inline where it fits (see decision 2), else overlay | as Compact |
+
+And one promise across all three: **no action is ever unreachable.**
+That is the sentence #69 asks for and it is the one the matrix exists
+to make checkable.
+
+**400% zoom** keeps the meaning it already has: WCAG 1.4.10 names 320px
+as the reflow target, the phone band covers it, and
+`layout-overflow.spec.ts` already asserts a 320px viewport needs no
+sideways scrolling. What changes is that the *queue* must be part of
+that assertion — it is not today, and with the queue open at 320px the
+main panel is 0px wide, which no current test can see.
+
+**The window minimum stays 800×600**, and its comment gets the real
+reason. The old mechanisms are gone, but the floor is still where the
+Compact band's chrome stops being comfortable, and lowering it would
+mean promising the desktop layout at sizes where only the phone layout
+works. The interesting consequence is decision 4.
+
+---
+
+## Decision 2 — the queue is an overlay when it cannot afford to be a column
+
+**The rule.** The queue panel renders inline — in the flow, as today —
+only while
+
+```
+viewport − sidebar − queueWidth ≥ 480
+```
+
+and as an overlay with a scrim otherwise.
+
+**Why it cannot be a media query**, which is the load-bearing half:
+the queue's width is *user state*. It is drag-resizable between 200 and
+500px and persisted (`--queue-width`, `MIN_WIDTH`/`MAX_WIDTH` in
+`queue-panel.ts`). A breakpoint at a fixed viewport width silently
+assumes the default 320, and is wrong by 180px for a user who has
+dragged the panel wide — in the direction that hurts, since a wider
+queue is exactly when the content can least afford it. So the mode is
+computed from the measured widths and published as an attribute, the
+way `data-active-view` already is, and the CSS keys off that.
+
+**Why 480, honestly.** There is no cliff to derive it from. The track
+list rescales its columns continuously — at main widths from 900 down
+to 544 its `--grid-cols` shrink from 213px to 124px with
+`rowOverflow=0` throughout — and the album grid steps 3 columns to 2
+somewhere between 564 and 644 without breaking. So this is a judgement,
+anchored on two things: it keeps the *default* window (1100 wide, main
+= 580) inline, because the inline queue is a desktop affordance people
+choose and turning it into an overlay for the common case would be a
+regression in feel; and it puts every case measured as broken —
+900×600 at main=379, and every phone width — on the overlay side.
+1024×768 lands at main=504 and stays inline.
+
+**The scrim is the other half of the issue's complaint** ("make the
+queue obviously an overlay *over* the content so it reads as something
+to close"). An overlay queue gets a scrim, closes on scrim click and on
+Escape, and returns focus to `#queue-button`.
+
+**What must not change**: #55's Direction is explicit — one component,
+two mount points, do not fork it. The overlay is a *presentation* of
+the same `queue-panel`, so the roving tab stop, Alt+Arrow reorder, drag
+reorder, selection semantics and the `virtualizer.requestUpdate()` on
+selection and current-track change all come along untouched. This
+decision deliberately stops short of #55's detail-view mount, but it is
+the shape that makes it possible, and it unblocks it.
+
+---
+
+## Decision 3 — #69 is its own PR, and here is the finding that decides it
+
+`page-header` **cannot collapse its own actions**, and that is not an
+effort estimate but a fact about the API. Actions arrive through
+`<slot name="actions">` as arbitrary light-DOM markup — Playlists slots
+a `<div class="header-actions">` of three `<button>`s with click
+handlers, drag handlers and a conditional class. A component cannot
+move another component's light-DOM children into a dropdown and keep
+their behaviour; there is nothing generic to render as a menu item.
+
+So the overflow rule needs an *actions API* — hosts declaring
+`{icon, label, handler, priority}` data that `page-header` can render
+either as buttons or as menu items — which is a change to all three
+hosts that slot actions, not a rule added in one place. That is a
+different piece of work from this one, it is independently verifiable,
+and the desktop half of #69's symptom is removed by decision 2 anyway
+(the queue stops eating the header's width).
+
+It therefore stays #69, gets the finding above recorded on it, and
+follows immediately after this. What *this* plan owes it is the
+promise in the matrix — no action unreachable at any supported size —
+and the measurement that the only offender today is Playlists.
+
+**And the promise is not kept yet, which is the honest version of a
+claim this document made in its first draft.** "Decision 2 removes the
+desktop half of #69's symptom" was too strong. Measured after phase 2,
+at 900×600 on Playlists:
+
+| | before | after |
+|---|---|---|
+| queue open | main 379px, **all three** actions clipped | main 700px, **one** clipped |
+| queue closed | main 700px, one clipped | unchanged |
+
+So the queue's *contribution* is gone — open and closed are now
+identical, which is the whole of what this decision owed — and the
+residual "New Smart Playlist: 114/162px" is the header overflowing on
+its own, at a size the queue never touched. #69 is still a live defect
+at a supported size, and the matrix's promise is what will close it.
+
+---
+
+## Decision 4 — a very small window becomes the phone layout, not the mini-player
+
+#24 asks whether a very small window should switch to the mini-player
+(#12) "or simply refuse to go there". Both options in the question are
+worse than the one the codebase already has.
+
+**#12 is a second window, not a mode.** Its findings say so: v3
+supports multiple windows, `AlwaysOnTop` is a window *option*, and the
+frontend would need an entry branch mounting only the mini-player root
+for a second window loading the same bundle. Turning the main window
+into a mini-player at some width conflates the two: it would throw away
+the user's navigation state on a resize, and it puts the MPRIS question
+(#12's own open question — media controls are process-level and must
+not be per-window) on a code path that a drag can trigger by accident.
+
+**And "refuses" is unnecessary, because the reflow already exists.**
+The phone band is real, tested, and reached by width alone — a desktop
+window narrowed below 600px already gets `bottom-nav` and the phone
+shell. That is a better answer than refusing: it is strictly more
+usable than a hard minimum, it costs nothing new, and it is the same
+code Android runs, so it stays exercised.
+
+So: the main window reflows and never becomes a mini-player; #12 stays
+a separate always-on-top window and is not blocked by, or coupled to,
+this decision. The window minimum stays 800×600 for the reason in
+decision 1 — but the phone band is what happens below it, not a
+refusal, which is why the minimum is a comfort floor rather than a
+correctness one.
+
+---
+
+## Phases
+
+1. **This document**, linked from #24, with the matrix reported on the
+   issue and #55 told whether it is unblocked. *(no code)* — **done**
+2. **The queue's overlay mode** — computed mode attribute, scrim,
+   Escape and scrim-click close, focus return. The inline path is
+   unchanged above the threshold. — **done**
+3. **The window minimum's comment** — replace both stale reasons with
+   the measured ones. No value change. — **done**
+4. **Verification**, below. Including the specs that must change
+   because they assert the old behaviour. — **done**
+
+#69 follows as its own branch; #55 became unblocked at phase 2.
+
+## What landed, measured
+
+Main panel width with the queue open, before and after:
+
+| viewport | before | after | mode |
+|---|---|---|---|
+| 1280×800 | 759 | 759 | inline |
+| 1100×720 (default window) | 579 | 579 | inline |
+| 1024×768 | 503 | 503 | inline |
+| 900×600 | **379** | **700** | overlay |
+| 800×600 | 423 | 744 | overlay |
+| 390×780 | **69** | **390** | overlay |
+| 320×600 | **0** | **320** | overlay |
+
+The scrim is perceptible but subtle on a dark ramp, which is worth
+knowing before someone "fixes" it: sampled from the screenshots at
+900×600, the main panel's background goes 33,37,41 → 18,20,23 and a
+row's text 242 → 133. It covers the **content area only** — not the
+sidebar or the transport — on purpose: the queue is not modal, and
+leaving the navigation live means the scrim reads as "this is over the
+content" (which is what #24 asked for) without pretending the rest of
+the app is unavailable.
+
+## Verification, and what each tier cannot see
+
+- `make ui-test` — the queue panel's mode logic is component-tier
+  work and belongs there. It **cannot** see the shell: the threshold is
+  computed from the sidebar and viewport, which do not exist in that
+  tier.
+- `make e2e` — `layout-overflow.spec.ts` gains the queue-open case at
+  every band (it has none today, which is why main=0px at 320px has
+  never failed anything) and **gains 900×600**, since the minimum is
+  not the worst case. `queue-toggle-state.spec.ts` and
+  `phone-shell.spec.ts` both touch the panel and must be re-read before
+  editing.
+- **Screenshots at every band, read by a human.** This is not optional
+  here: `layout-overflow.spec.ts` asserts the *shell* needs no sideways
+  scrolling and passes on a build whose album header clips its own
+  buttons (measured this session at 390px; filed on #66). Clipping
+  *inside* a component is invisible to it, and clipping is this issue.
+- `make ui-visual` **cannot help at all** — the component tier renders
+  the token fallbacks, because the theme only reaches `:root` in the
+  real app.
+- Accessible names via `page.getByRole(...)`, never a shadow-root
+  query. A drawer with a scrim is exactly the shape that grows a
+  nameless control, and this repo has shipped one three times.

CLAUDE.md

@@ -1328,6 +1328,68 @@ is 32px each. Which four is plan 016's committed subset, and everything
 else — Settings included, because a phone still needs it — is behind
 "More".
 
+**There are three supported size bands, and the queue is part of the
+promise.** Plan 018 (#24) wrote them down: **Phone** below 600 (bottom
+nav, reflows, fits 320px exactly), **Compact** 600–899 (icon sidebar),
+**Desktop** from 900 (labelled sidebar) — plus one sentence across all
+three, *no action is ever unreachable at any supported size*. The bands
+themselves already existed; what was new is that they are a promise and
+that the queue panel is inside it.
+
+**900 is the worst desktop width, not the 800×600 minimum.** The
+sidebar collapses to icons *below* 900, so the main panel is 843px at
+899 and 700px at 900 — the narrowest content area any desktop width
+produces is at the top of the Compact band, not at the enforced floor.
+Every viewport list that stopped at "the minimum" was therefore missing
+its own worst case, which is why `layout-overflow.spec.ts` carries 900
+now. And **both reasons in `MinWidth`'s comment had expired** — the
+subtitle is `display: none` from 899 down and the sidebar host scrolls
+(`overflow-y: auto`; at 600×460 its `scrollHeight` is 434 against a
+332px client) — so 800×600 is a *comfort* floor for desktop chrome and
+not a correctness one. Below it the phone layout takes over, which is
+also why a very small window reflows rather than becoming a
+mini-player: **#12 is a second always-on-top window, not a mode of this
+one**, and making it a mode would discard navigation state on a resize
+and put the process-level MPRIS question on a path a drag can trigger.
+
+**The queue panel is a column only while the content can spare the
+width, and that cannot be a media query.** In flow the host is
+`flex-shrink: 0`, so an open queue is paid for by the main panel: it
+left 379px at 900×600 (with all three of the Playlists header's actions
+clipped), 69px at 390, and **0px** at 320 — the content was not
+degraded but gone. It goes to an overlay with a scrim when
+`available - panelWidth < 480`, where `available` is
+`.content-area`'s width and therefore already accounts for the
+sidebar's collapse.
+
+Four things about it are load-bearing. **The mode is computed, not
+breakpointed**, because the panel's width is user state — drag-resizable
+200–500px and persisted — so a viewport breakpoint silently assumes the
+default 320 and is wrong by up to 180px in the direction that hurts;
+widening the panel at a fixed window size must flip it, and
+`queue-overlay-mode.test.ts` is written around exactly that. **480 is a
+judgement and says so**: there is no cliff to derive it from (the track
+list rescales continuously, 213px to 124px columns with no row
+overflow), so it is anchored to keep the default 1100px window inline
+and put every measured-broken case on the overlay side. **The scrim
+covers the content area only** — not the sidebar or the transport —
+because the queue is not modal, and it is subtle on a dark ramp by
+arithmetic rather than by accident (33,37,41 → 18,20,23). And **the
+overlay is a presentation, not a fork**: #55 asks for one component
+with two mount points, so the roving tab stop, Alt+Arrow reorder, drag
+reorder, selection semantics and `virtualizer.requestUpdate()` all come
+along untouched. Escape closes it and returns focus, and is attached
+only while the overlay is up — it is a dismissal, not a shortcut, which
+is why it is not a panel-scoped binding.
+
+What this does **not** fix is `page-header` overflowing on its own:
+at 900×600 "New Smart Playlist" is still clipped to 114 of 162px with
+the queue *closed*. That is #69, and it cannot be fixed in
+`page-header` alone — actions arrive through `<slot name="actions">` as
+arbitrary light-DOM markup with their own handlers, so collapsing them
+into a "More actions" menu needs an actions *API* (data, not markup)
+across all three hosts that slot them.
+
 **The phone section of `index.css` is last on purpose.** A media query
 adds no specificity, so a `@media (max-width: 599px)` block placed
 above the plain rules it overrides loses to them — which is how phase 1
@@ -2307,6 +2369,23 @@ Pre-commit hooks verify generated code is fresh — always run `make generate` a
   mistyped `feat` ships a minor version. `make release-dry` answers "what
   would this merge release" without pushing.
 
+  **The analyzer reads the type and ignores the scope, so a CI-only change
+  is `ci:` and never `fix(ci):`.** The scope is decoration; `fix` is a
+  patch whatever is in the brackets. Two commits touching nothing but
+  `.gitea/workflows/unclaim.yml` were written `fix(ci):` and cut `v0.2.1`
+  and `v0.2.2` — real releases, published to Arch, Homebrew and the APK
+  registry, containing no user-facing change. They were left in place
+  rather than deleted, because a version that vanishes is worse for
+  whoever pulled it than one that turns out to be empty.
+
+  **The blast radius is bigger than the version number**, which is what
+  makes this worth a paragraph. A merge to `main` starts two workflows;
+  if `release.yml` then pushes a tag, that tag push starts **four more**
+  (`arch-package`, `homebrew-formula`, `android-apk`, `desktop-assets`) —
+  on a runner with capacity 1, where the APK build alone is tens of
+  minutes. `make release-dry` before merging is how you find out, and it
+  is cheaper than every one of those.
+
   **`@semantic-release/github` is not in that config and must not be.**
   Gitea's API is `/api/v1` and is not GitHub's surface, so
   `@semantic-release/exec` calls `scripts/gitea-release.sh` instead — one

backend/config/window.go

@@ -13,13 +13,31 @@ const (
 	// enforces this at runtime; it is also the floor below which a
 	// reported size is treated as bogus and not persisted.
 	//
-	// 800x600 is where the shell was measured to still work, rather
-	// than a round number: below ~780 the header's subtitle wraps and
-	// pushes the title out of the 4em top bar, and below ~600 tall the
-	// eleven sidebar items no longer fit at once.  The previous
-	// 512x384 was aspirational — at 700x480 the sidebar overflowed
-	// behind the player bar with no scroll and Settings and Jobs could
-	// not be reached at all.
+	// **Both reasons this comment used to give have expired**, and the
+	// value is right for a third one.  It said the floor was 800x600
+	// because "below ~780 the header's subtitle wraps and pushes the
+	// title out of the 4em top bar" and "below ~600 tall the eleven
+	// sidebar items no longer fit at once".  Neither mechanism can
+	// happen now: the subtitle is display:none from 899px down
+	// (index.css), and the sidebar host is overflow-y:auto — measured
+	// at 600x460, its scrollHeight is 434 against a 332px client and
+	// Settings is reachable after scrolling.  A floor defended by two
+	// mechanisms that no longer exist is a number nobody can argue
+	// with, which is worse than either answer.
+	//
+	// It stays 800x600 because that is where the *desktop* chrome
+	// stops being comfortable — the Compact band of plan 018's size
+	// matrix (#24) — and not because the app breaks below it.  It does
+	// not: under 600px wide the phone layout takes over (bottom-nav,
+	// no sidebar) and the shell fits 320px exactly, which is what
+	// makes this a comfort floor rather than a correctness one, and
+	// why a very small window reflows instead of becoming a
+	// mini-player (#12 is a second always-on-top window, not a mode of
+	// this one).
+	//
+	// The previous 512x384 was aspirational — at 700x480 the sidebar
+	// overflowed behind the player bar with no scroll and Settings and
+	// Jobs could not be reached at all.
 	MinWidth = 800
 	// MinHeight is the smallest allowed window height in pixels.
 	MinHeight = 600

backend/player/buffered_stall_test.go

@@ -0,0 +1,188 @@
+package player
+
+import (
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/gopxl/beep/v2"
+)
+
+// errTestDecode stands in for a decoder blowing up mid-track.
+var errTestDecode = errors.New("decode blew up")
+
+// stalledStreamer never produces a sample and never reports
+// end-of-stream: (0, true), forever. A damaged file that decodes to
+// nothing looks like this, and so does any source whose producer has
+// quietly stopped.
+type stalledStreamer struct{}
+
+func (stalledStreamer) Stream(_ [][2]float64) (int, bool) { return 0, true }
+func (stalledStreamer) Err() error                        { return nil }
+
+// failingStreamer produces n good samples and then fails, which is
+// what a decode error mid-track looks like: the same (0, false) a
+// finished track returns, distinguishable only by Err.
+type failingStreamer struct {
+	remaining int
+	err       error
+}
+
+func (f *failingStreamer) Stream(samples [][2]float64) (int, bool) {
+	if f.remaining <= 0 {
+		return 0, false
+	}
+
+	n := min(len(samples), f.remaining)
+
+	for i := range n {
+		samples[i] = [2]float64{1, 1}
+	}
+
+	f.remaining -= n
+
+	return n, true
+}
+
+func (f *failingStreamer) Err() error { return f.err }
+
+// drainUntilEnd calls Stream until it reports end-of-stream, or gives
+// up. It returns whether the stream ended.
+//
+// The give-up bound is wall clock rather than a call count: the stall
+// budget is a duration, so a tight loop has to actually wait it out.
+func drainUntilEnd(bs *BufferedStreamer, within time.Duration) bool {
+	buf := make([][2]float64, 512)
+	deadline := time.Now().Add(within)
+
+	for time.Now().Before(deadline) {
+		if _, ok := bs.Stream(buf); !ok {
+			return true
+		}
+
+		time.Sleep(time.Millisecond)
+	}
+
+	return false
+}
+
+// A source that stops producing without ever ending is the fault this
+// whole file exists for: Stream used to answer with silence and ok
+// forever, so the chain never ended, the player stayed in Playing
+// with the button showing pause, and the decoder's position never
+// moved -- a frozen seek bar over a track that was not playing.
+func TestAStalledSourceEndsTheStream(t *testing.T) {
+	bs := NewBufferedStreamer(stalledStreamer{}, 2048)
+	defer bs.Close()
+
+	if !drainUntilEnd(bs, maxStarvedDuration+2*time.Second) {
+		t.Fatal(
+			"a stalled source never ended the stream: the player " +
+				"would sit in Playing with a frozen position",
+		)
+	}
+
+	if !errors.Is(bs.Err(), errSourceStalled) {
+		t.Fatalf(
+			"expected the stall to be reported, got %v", bs.Err(),
+		)
+	}
+}
+
+// Close is the other exit that used to leave `done` false, with the
+// same consequence: the ring drains and every call after it is
+// silence that claims to be audio.
+func TestClosingEndsTheStream(t *testing.T) {
+	bs := NewBufferedStreamer(finiteStreamer(1<<20), 2048)
+
+	// Let the read-ahead fill something, so this exercises the drain
+	// after Close rather than a buffer that was empty anyway.
+	time.Sleep(20 * time.Millisecond)
+	bs.Close()
+
+	if !drainUntilEnd(bs, 2*time.Second) {
+		t.Fatal("a closed streamer never reported end-of-stream")
+	}
+}
+
+// A source that fails is not a source that finished, and only Err
+// tells them apart. Before this, the player reported a mid-track
+// decode failure to the queue as a natural end, so the queue
+// auto-advanced in silence and counted the broken track as played.
+func TestAFailedSourceReportsItsError(t *testing.T) {
+	src := &failingStreamer{remaining: 4096, err: errTestDecode}
+
+	bs := NewBufferedStreamer(src, 2048)
+	defer bs.Close()
+
+	if !drainUntilEnd(bs, 2*time.Second) {
+		t.Fatal("a failing source never reported end-of-stream")
+	}
+
+	if !errors.Is(bs.Err(), errTestDecode) {
+		t.Fatalf(
+			"expected the source's error to survive, got %v",
+			bs.Err(),
+		)
+	}
+}
+
+// The ordinary case has to keep working: a source that ends cleanly
+// ends with no error, or every finished track would be reported as a
+// failure and skipped.
+func TestADrainedSourceReportsNoError(t *testing.T) {
+	bs := NewBufferedStreamer(finiteStreamer(4096), 2048)
+	defer bs.Close()
+
+	if !drainUntilEnd(bs, 2*time.Second) {
+		t.Fatal("a finite source never reported end-of-stream")
+	}
+
+	if bs.Err() != nil {
+		t.Fatalf(
+			"a track that finished normally reported %v", bs.Err(),
+		)
+	}
+}
+
+// A slow source is exactly what the read-ahead exists to absorb, so
+// underruns must not be charged cumulatively -- otherwise a file on a
+// slow disk ends itself partway through.
+func TestUnderrunsDoNotAccumulateAcrossASlowSource(t *testing.T) {
+	const total = 8192
+
+	src := &slowStreamer{
+		inner: finiteStreamer(total),
+		delay: 2 * time.Millisecond,
+	}
+
+	bs := NewBufferedStreamer(src, 1024)
+	defer bs.Close()
+
+	buf := make([][2]float64, 256)
+	got := 0
+
+	for {
+		n, ok := bs.Stream(buf)
+		if !ok {
+			break
+		}
+
+		for i := range n {
+			if buf[i][0] != 0 {
+				got++
+			}
+		}
+	}
+
+	if got != total {
+		t.Fatalf(
+			"a slow but healthy source was cut short: got %d of %d "+
+				"samples",
+			got, total,
+		)
+	}
+}
+
+// beep.Streamer is what the player wraps; keep the type honest.
+var _ beep.Streamer = (*BufferedStreamer)(nil)

backend/player/buffered_streamer.go

@@ -1,6 +1,7 @@
 package player
 
 import (
+	"errors"
 	"sync"
 	"time"
 
@@ -34,8 +35,45 @@ type BufferedStreamer struct {
 	done    bool
 	err     error
 	closed  chan struct{}
+
+	// starved counts consecutive Stream calls served with silence
+	// because the ring was empty, and starvedSince is when that run
+	// began.  An underrun is legitimate for a moment -- that is what
+	// the read-ahead exists to absorb -- but it is not legitimate
+	// forever, and "forever" is indistinguishable from healthy
+	// playback everywhere above this type: the chain never ends, so
+	// the player stays in Playing with the button showing pause, and
+	// the decoder's position never moves, so the 1 Hz report pins the
+	// seek bar and suppresses its interpolation.
+	starved      int
+	starvedSince time.Time
 }
 
+// The silence fill is bounded by both a duration and a run of calls,
+// and it needs both.
+//
+// Duration alone is the real measure -- the speaker paces itself, so
+// wall clock is what says whether the source has actually stopped --
+// but a caller draining in a tight loop (a test, a decode-to-buffer)
+// makes hundreds of calls in microseconds and would trip nothing.
+// A call count alone is the opposite failure: the same tight loop
+// spends the whole budget before the read-ahead goroutine has been
+// scheduled once, and ends a perfectly good stream at sample zero.
+//
+// The duration is longer than the 2 s read-ahead it is there to
+// outlast, and the count is short enough that the speaker (~200 ms a
+// call) reaches it well inside that.
+const (
+	maxStarvedDuration = 3 * time.Second
+	minStarvedCalls    = 8
+)
+
+// errSourceStalled is returned by Err when the source stopped
+// producing samples without ever reporting end-of-stream.
+var errSourceStalled = errors.New(
+	"audio source stopped producing samples",
+)
+
 // NewBufferedStreamer creates a BufferedStreamer that pre-fills
 // bufferSize samples from source via a background goroutine.
 // A typical bufferSize is 2× the sample rate (~2 seconds of audio).
@@ -54,8 +92,24 @@ func NewBufferedStreamer(
 	return bs
 }
 
+// finish marks the stream ended, recording err as the reason when
+// there is one.  Every exit from readAhead goes through it: an exit
+// that leaves done false strands Stream in its underrun branch,
+// where it returns silence and ok forever.
+func (bs *BufferedStreamer) finish(err error) {
+	bs.mu.Lock()
+	defer bs.mu.Unlock()
+
+	bs.done = true
+
+	if err != nil && bs.err == nil {
+		bs.err = err
+	}
+}
+
 // readAhead continuously reads from the source into the ring buffer
 // until the source is drained, an error occurs, or Close is called.
+// It always marks the stream done on the way out.
 func (bs *BufferedStreamer) readAhead() {
 	// Temporary buffer for reading from source outside the lock.
 	// 512 samples per chunk keeps the critical section short.
@@ -63,6 +117,13 @@ func (bs *BufferedStreamer) readAhead() {
 
 	tmp := make([][2]float64, chunkSize)
 
+	// Every exit marks the stream done.  An exit that does not is what
+	// stranded Stream in its underrun branch, returning silence and ok
+	// for the rest of the process's life.
+	var exitErr error
+
+	defer func() { bs.finish(exitErr) }()
+
 	for {
 		// Check if closed.
 		select {
@@ -72,6 +133,15 @@ func (bs *BufferedStreamer) readAhead() {
 		}
 
 		bs.mu.Lock()
+
+		// Stream gave up waiting for us.  Nothing downstream is
+		// listening any more, so filling the ring is work for nobody.
+		if bs.done {
+			bs.mu.Unlock()
+
+			return
+		}
+
 		space := len(bs.ring) - bs.count
 
 		if space == 0 {
@@ -115,14 +185,12 @@ func (bs *BufferedStreamer) readAhead() {
 		}
 
 		if !ok {
-			bs.mu.Lock()
-			bs.done = true
-
-			if srcErr := bs.source.Err(); srcErr != nil {
-				bs.err = srcErr
-			}
-
-			bs.mu.Unlock()
+			// A drained source and a failed one both land here and are
+			// not the same event: one is a track that ended, the other
+			// is a track that broke.  Err is what tells them apart, and
+			// it is why the player must ask before treating this as a
+			// natural finish.
+			exitErr = bs.source.Err()
 
 			return
 		}
@@ -154,7 +222,27 @@ func (bs *BufferedStreamer) Stream(
 	}
 
 	if bs.count == 0 {
-		// Buffer temporarily empty — fill with silence.
+		// The read-ahead has not caught up.  Silence buys it time --
+		// but only for a bounded stretch, because "forever" is
+		// reported upward as healthy playback and there is no watchdog
+		// above this to notice otherwise.
+		bs.starved++
+
+		if bs.starvedSince.IsZero() {
+			bs.starvedSince = time.Now()
+		}
+
+		if bs.starved >= minStarvedCalls &&
+			time.Since(bs.starvedSince) > maxStarvedDuration {
+			bs.done = true
+
+			if bs.err == nil {
+				bs.err = errSourceStalled
+			}
+
+			return 0, false
+		}
+
 		for i := range samples {
 			samples[i] = [2]float64{}
 		}
@@ -162,6 +250,9 @@ func (bs *BufferedStreamer) Stream(
 		return len(samples), true
 	}
 
+	// Samples arrived, so whatever the stall was, it is over.
+	bs.resetStarvationLocked()
+
 	// Copy available samples from ring buffer.
 	n := len(samples)
 	if n > bs.count {
@@ -197,6 +288,19 @@ func (bs *BufferedStreamer) Flush() {
 	bs.readPos = 0
 	bs.writPos = 0
 	bs.count = 0
+
+	// A seek empties the ring on purpose, and the refill that follows
+	// is exactly the stall the budget exists to tolerate.  Charging it
+	// against a budget the previous underrun already spent would end
+	// the track on a seek near the end of a slow file.
+	bs.resetStarvationLocked()
+}
+
+// resetStarvationLocked forgets an underrun run.  Must be called with
+// bs.mu held.
+func (bs *BufferedStreamer) resetStarvationLocked() {
+	bs.starved = 0
+	bs.starvedSince = time.Time{}
 }
 
 // LockSource blocks the read-ahead goroutine from touching the

backend/player/loadstate_test.go

@@ -0,0 +1,213 @@
+package player
+
+import (
+	"log/slog"
+	"testing"
+	"time"
+
+	"github.com/wailsapp/wails/v3/pkg/application"
+
+	"yellowjacket/backend/events"
+	"yellowjacket/internal/testfixtures"
+)
+
+// fixtureSampleRate is what cmd/gentestdata writes (audio.go).  It is
+// deliberately not the speaker rate, which is what lets these tests
+// tell the decoder's format from the player's default.
+const fixtureSampleRate = 22050
+
+// newTestPlayer is a player with a context and no database, so the
+// track-metadata lookup cannot succeed.
+func newTestPlayer(t *testing.T) *Player {
+	t.Helper()
+
+	p := NewPlayer(slog.Default(), nil)
+	rec := events.NewRecorder()
+
+	_ = p.ServiceStartup(
+		events.WithSink(t.Context(), rec),
+		application.ServiceOptions{},
+	)
+
+	return p
+}
+
+// loadFileLocked needs no speaker: it decodes, builds the chain and
+// registers it paused. speaker.Play on an uninitialised device is
+// what the integration guard elsewhere is about, so these assert on
+// the state the load computed rather than on playback.
+
+// p.format used to be assigned once, in the constructor, to the
+// *speaker's* rate -- so it claimed 44.1 kHz for every file ever
+// loaded. Play()'s replay-after-finish path resamples from it, so a
+// finished track played again was resampled from a rate the decoder
+// never produced: audibly the wrong speed and pitch, and wrong
+// length and position arithmetic with it.
+//
+// The fixtures are 22050 Hz, which is exactly the point -- any of
+// them disagrees with the speaker rate.
+func TestLoadRecordsTheDecodersOwnFormat(t *testing.T) {
+	m := testfixtures.Load(t)
+	path := m.Case(t, testfixtures.CaseCoverDedup)[0]
+
+	p := newTestPlayer(t)
+
+	if got := p.format.SampleRate; got != speakerSampleRate {
+		t.Fatalf(
+			"precondition: a fresh player should hold the speaker "+
+				"rate, got %d",
+			got,
+		)
+	}
+
+	if err := p.LoadFile(path); err != nil {
+		t.Fatalf("LoadFile(%s): %v", path, err)
+	}
+
+	if p.format.SampleRate == speakerSampleRate {
+		t.Fatalf(
+			"p.format still holds the speaker rate (%d) after "+
+				"loading a %d Hz file: the replay path would "+
+				"resample from the wrong rate",
+			speakerSampleRate, fixtureSampleRate,
+		)
+	}
+
+	if got := int(p.format.SampleRate); got != fixtureSampleRate {
+		t.Errorf(
+			"expected the decoder's rate %d, got %d",
+			fixtureSampleRate, got,
+		)
+	}
+}
+
+// trackLengthMs is written only when the database has a row for the
+// file and cleared only by UnloadTrack, so a track with no row used
+// to inherit whatever the last track's duration was -- and every
+// position report is scaled by it, so the whole seek bar was then
+// reporting one track's progress on another track's scale.
+//
+// There is no database here, so the lookup cannot succeed: exactly
+// the case that used to inherit.
+func TestLoadDoesNotInheritThePreviousTracksDuration(t *testing.T) {
+	m := testfixtures.Load(t)
+	path := m.Case(t, testfixtures.CaseCoverDedup)[0]
+
+	p := newTestPlayer(t)
+
+	// Stand in for a previous track whose duration was resolved.
+	p.trackLengthMs = 9_999_000
+
+	if err := p.LoadFile(path); err != nil {
+		t.Fatalf("LoadFile(%s): %v", path, err)
+	}
+
+	if p.trackLengthMs == 9_999_000 {
+		t.Fatal(
+			"the previous track's duration survived the load: every " +
+				"position report for this track would be scaled by it",
+		)
+	}
+}
+
+// A new chain supersedes the old one's pending finished callback.
+// Without this, a callback that queued for p.mu behind a LoadFile
+// woke up and rewound, stopped and auto-advanced the *new* track.
+func TestANewChainSupersedesTheOldFinishedCallback(t *testing.T) {
+	m := testfixtures.Load(t)
+	paths := m.Case(t, testfixtures.CaseCoverDedup)
+
+	if len(paths) < 2 {
+		t.Skip("need two fixture tracks")
+	}
+
+	p := newTestPlayer(t)
+
+	if err := p.LoadFile(paths[0]); err != nil {
+		t.Fatalf("LoadFile(%s): %v", paths[0], err)
+	}
+
+	stale := p.chainID
+
+	if err := p.LoadFile(paths[1]); err != nil {
+		t.Fatalf("LoadFile(%s): %v", paths[1], err)
+	}
+
+	if p.chainID == stale {
+		t.Fatal("loading a second file did not supersede the chain")
+	}
+
+	called := false
+
+	p.SetPlaybackFinishedHandler(func(error) { called = true })
+
+	// The first track's callback, arriving late.
+	p.onPlaybackFinished(stale, nil)
+
+	if called {
+		t.Error(
+			"a superseded chain's callback drove auto-advance: the " +
+				"track that is loaded now would be skipped",
+		)
+	}
+
+	if p.state == Stopped {
+		t.Error(
+			"a superseded chain's callback stopped the current track",
+		)
+	}
+}
+
+// The decoder is read by the read-ahead goroutine and by every
+// position emit, and those used to be guarded by different mutexes:
+// the read by srcMu, the position by the speaker lock, which
+// read-ahead never takes. Under -race this failed on the emit that
+// LoadFile itself makes.
+//
+// It needs the read-ahead goroutine to actually be running, so it
+// keeps asking for the position for long enough to overlap it.
+func TestPositionReadsDoNotRaceTheReadAhead(t *testing.T) {
+	m := testfixtures.Load(t)
+	path := m.Case(t, testfixtures.CaseFLACAlbum)[0]
+
+	p := newTestPlayer(t)
+
+	if err := p.LoadFile(path); err != nil {
+		t.Fatalf("LoadFile(%s): %v", path, err)
+	}
+
+	for range 200 {
+		if _, err := p.CurrentPositionSeconds(); err != nil {
+			t.Fatalf("CurrentPositionSeconds: %v", err)
+		}
+	}
+}
+
+// Seeking emits the landing position, and that emit reads the
+// decoder -- so the source lock the seek holds must be released
+// before it. A reentrant take here is a deadlock, not a failure,
+// which is why this test exists rather than a comment.
+func TestSeekEmitsWithoutDeadlocking(t *testing.T) {
+	m := testfixtures.Load(t)
+	path := m.Case(t, testfixtures.CaseFLACAlbum)[0]
+
+	p := newTestPlayer(t)
+
+	if err := p.LoadFile(path); err != nil {
+		t.Fatalf("LoadFile(%s): %v", path, err)
+	}
+
+	done := make(chan struct{})
+
+	go func() {
+		defer close(done)
+
+		_ = p.Seek(1)
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(10 * time.Second):
+		t.Fatal("Seek deadlocked: the position emit re-took the source lock")
+	}
+}

backend/player/player.go

@@ -52,9 +52,17 @@ type Player struct {
 	control                 *beep.Ctrl
 	volume                  *effects.Volume
 	speakerStreamer         beep.Streamer
-	playbackFinishedHandler func()
+	playbackFinishedHandler func(error)
 	trackChangeID           uint64
-	mediaControls           mediacontrols.Handler
+
+	// chainID identifies the streamer chain currently registered with
+	// the speaker.  updateStreamers bumps it, and the finished
+	// callback carries the value it was registered with, so a callback
+	// that queued for p.mu behind a LoadFile can tell that the player
+	// has moved on and return rather than rewinding somebody else's
+	// track.
+	chainID       uint64
+	mediaControls mediacontrols.Handler
 
 	// duckAmount is the attenuation currently applied on top of the
 	// user's volume, in the same base-2 exponent effects.Volume uses.
@@ -180,11 +188,18 @@ func (p *Player) InitSpeaker() error {
 }
 
 // SetPlaybackFinishedHandler sets a callback invoked when a track
-// finishes naturally. This allows the queue to drive auto-advance
+// stops streaming. This allows the queue to drive auto-advance
 // without circular imports.
 //
+// The error says *why* the track stopped: nil for a track that
+// reached its end, non-nil for one that broke partway through.  Both
+// arrive here because both look identical to the speaker, and only
+// the queue holds the metadata a PlaybackFailed needs -- but they are
+// not the same event, and reporting a decode failure as a natural
+// finish is how a broken file used to auto-advance in silence.
+//
 //wails:ignore // internal wiring, not part of the app's IPC surface.
-func (p *Player) SetPlaybackFinishedHandler(handler func()) {
+func (p *Player) SetPlaybackFinishedHandler(handler func(error)) {
 	p.mu.Lock()
 	defer p.mu.Unlock()
 
@@ -424,6 +439,19 @@ func (p *Player) updateStreamers(
 	newBaseStreamer beep.StreamSeeker,
 	sr beep.SampleRate,
 ) error {
+	// A new chain supersedes the old one, so any finished callback the
+	// old one still owes is stale from here on.
+	p.chainID++
+
+	// The previous read-ahead goroutine reads the same decoder this
+	// one is about to, under its own srcMu -- two goroutines, two
+	// mutexes, one decoder that is not safe for concurrent use.  The
+	// replay-after-finish path rebuilds from p.seeker without going
+	// through LoadFile, which is where that pair could meet.
+	if p.buffered != nil {
+		p.buffered.Close()
+	}
+
 	// set base streamer
 	p.baseStreamer = newBaseStreamer
 	p.seeker = newBaseStreamer
@@ -474,23 +502,57 @@ func (p *Player) startPaused() {
 	p.control.Paused = true
 	speaker.Unlock()
 
+	// Captured, not read at callback time: by then p.chainID names
+	// whatever is loaded *now*, which is the thing the guard exists to
+	// distinguish this chain from.
+	chainID := p.chainID
+	buffered := p.buffered
+
 	// The beep.Callback runs with the speaker mutex held, so we
 	// dispatch to a goroutine that can safely acquire p.mu.
 	speaker.Play(beep.Seq(
 		p.speakerStreamer,
 		beep.Callback(func() {
-			go p.onPlaybackFinished()
+			// Asked here rather than under p.mu: this is the chain that
+			// just ended, and by the time the goroutine holds the lock
+			// p.buffered may be a different one.
+			var err error
+			if buffered != nil {
+				err = buffered.Err()
+			}
+
+			go p.onPlaybackFinished(chainID, err)
 		}),
 	))
 
 	p.state = Paused
 }
 
-// onPlaybackFinished handles the natural end of a track. It is
-// called on a new goroutine from the beep callback (which holds
-// the speaker lock) so that it can safely acquire p.mu.
-func (p *Player) onPlaybackFinished() {
+// onPlaybackFinished handles a track that stopped streaming, whether
+// it ended or broke. It is called on a new goroutine from the beep
+// callback (which holds the speaker lock) so that it can safely
+// acquire p.mu.
+//
+// chainID names the streamer chain the callback fired for and srcErr
+// says why it stopped.
+func (p *Player) onPlaybackFinished(chainID uint64, srcErr error) {
 	p.mu.Lock()
+
+	// The player has moved on while this callback queued for the lock
+	// -- a user pressing Next during the last second of a track is
+	// enough. Everything below is about the *current* track: rewinding
+	// the decoder, saying playback stopped, asking the queue to
+	// advance. Doing any of it now would do it to the wrong track.
+	if chainID != p.chainID {
+		p.mu.Unlock()
+		p.logger.Debug(
+			"Ignoring finished callback for a superseded chain",
+			"chain", chainID, "current", p.chainID,
+		)
+
+		return
+	}
+
 	p.state = Stopped
 	handler := p.playbackFinishedHandler
 	mc := p.mediaControls
@@ -501,10 +563,11 @@ func (p *Player) onPlaybackFinished() {
 	// the Stopped state anyway, so this only moves the decoder.
 	p.rewindLocked()
 	p.emitPositionLocked()
-	p.mu.Unlock()
 
-	// Emit Wails events outside the lock — these are non-blocking
-	// calls that don't need player state.
+	// Emitted under p.mu, like every other transition in this file.
+	// Outside it, a Play() taking the lock in the gap emits `playing`
+	// first and this stale `stopped` lands last -- leaving the button
+	// showing play over a track that is audibly running.
 	p.emitPlaybackFinished()
 
 	events.Emit(
@@ -513,6 +576,8 @@ func (p *Player) onPlaybackFinished() {
 		map[string]string{"state": string(Stopped)},
 	)
 
+	p.mu.Unlock()
+
 	// Notify media controls outside the lock. The track just
 	// ended so position is 0.
 	if mc != nil {
@@ -521,12 +586,19 @@ func (p *Player) onPlaybackFinished() {
 		)
 	}
 
-	p.logger.Info("Playback finished naturally")
+	if srcErr != nil {
+		p.logger.Error(
+			"Playback stopped: the audio source failed",
+			"err", srcErr,
+		)
+	} else {
+		p.logger.Info("Playback finished naturally")
+	}
 
 	// Notify queue for auto-advance. Called without p.mu held
 	// because it re-enters the player via LoadFile/Play.
 	if handler != nil {
-		handler()
+		handler(srcErr)
 	}
 }
 
@@ -587,6 +659,18 @@ func (p *Player) loadFileLocked(filePath string) error {
 
 	p.currentFile = f
 
+	// The decoder's own format, kept for the paths that rebuild the
+	// chain later: Play()'s replay branch resamples from it, so a
+	// stale rate there plays a finished track back at the wrong speed.
+	p.format = format
+
+	// The previous track's duration must not outlive it.  This is set
+	// again by emitTrackChanged below, but only when the database has
+	// a row for the file -- and every position this player reports is
+	// scaled by it, so inheriting means every report is wrong by the
+	// ratio between two unrelated tracks.
+	p.trackLengthMs = 0
+
 	if err := p.updateStreamers(
 		streamer, format.SampleRate,
 	); err != nil {
@@ -906,6 +990,8 @@ func (p *Player) CurrentPosition() (int, error) {
 		return 0, errNoAudioFileLoaded
 	}
 
+	defer p.lockSourceLocked()()
+
 	speaker.Lock()
 	pos := math.Round(
 		100.0 * float64(p.seeker.Position()) /
@@ -924,6 +1010,28 @@ func (p *Player) Seek(targetSeconds int) error {
 	return p.seekLocked(targetSeconds)
 }
 
+// lockSourceLocked blocks the read-ahead goroutine from touching the
+// decoder and returns the function that releases it, so a caller can
+// `defer p.lockSourceLocked()()`.
+//
+// Reading the decoder's position is a read *of the decoder*, and the
+// speaker lock does not exclude the read-ahead goroutine -- it never
+// takes it.  That was a genuine data race on every position emit,
+// once a second for the whole of playback.
+//
+// srcMu is not reentrant, so nothing that already holds it may call
+// this; seekSourceLocked exists to keep that region free of emits.
+// Must be called with p.mu held.
+func (p *Player) lockSourceLocked() func() {
+	if p.buffered == nil {
+		return func() {}
+	}
+
+	p.buffered.LockSource()
+
+	return p.buffered.UnlockSource
+}
+
 // rewindLocked returns the decoder to the start of the track without
 // touching playback state.  Must be called with p.mu held.
 func (p *Player) rewindLocked() {
@@ -959,6 +1067,46 @@ func (p *Player) seekLocked(targetSeconds int) error {
 		return fmt.Errorf("cannot get track length: %w", err)
 	}
 
+	// The source lock is released before anything below is emitted:
+	// emitPositionLocked reads the decoder's position and takes the
+	// same lock, which is not reentrant.
+	seekErr := p.seekSourceLocked(targetSeconds, lengthSecs)
+	if seekErr != nil {
+		p.logger.Warn(
+			"Seek failed, playback will start from "+
+				"the beginning",
+			"target-seconds", targetSeconds,
+			"err", seekErr,
+		)
+
+		// The optimistic move the UI already made has to be taken
+		// back, and only the backend knows it did not happen.
+		events.Emit(p.ctx, events.SeekFailed)
+		p.emitPositionLocked()
+
+		return fmt.Errorf("failed to seek: %w", seekErr)
+	}
+
+	if p.mediaControls != nil {
+		p.mediaControls.NotifySeek(targetSeconds)
+	}
+
+	// Report the landing position immediately rather than leaving the
+	// UI to guess until the next tick — this is the half of H-3 that
+	// desynced the seek bar by 30 s over four keyboard seeks.
+	p.emitPositionLocked()
+
+	return nil
+}
+
+// seekSourceLocked moves the decoder and flushes the stale read-ahead
+// behind it.  It owns the source lock for exactly that long and
+// emits nothing, so its caller is free to read the position
+// afterwards.  Must be called with p.mu held.
+func (p *Player) seekSourceLocked(
+	targetSeconds int,
+	lengthSecs int,
+) error {
 	// Block the read-ahead goroutine from reading the source while
 	// we seek it. The decoder (e.g. FLAC's bufseekio.ReadSeeker) is
 	// not safe for concurrent Read+Seek, and read-ahead runs on its
@@ -1014,19 +1162,11 @@ func (p *Player) seekLocked(targetSeconds int) error {
 	if seekErr != nil {
 		speaker.Unlock()
 
-		p.logger.Warn(
-			"Seek failed, playback will start from "+
-				"the beginning",
-			"target-seconds", targetSeconds,
-			"samples", samples,
-			"err", seekErr,
+		p.logger.Debug(
+			"seek rejected by the decoder",
+			"samples", samples, "err", seekErr,
 		)
 
-		// The optimistic move the UI already made has to be taken
-		// back, and only the backend knows it did not happen.
-		events.Emit(p.ctx, events.SeekFailed)
-		p.emitPositionLocked()
-
 		return fmt.Errorf("failed to seek: %w", seekErr)
 	}
 
@@ -1039,15 +1179,6 @@ func (p *Player) seekLocked(targetSeconds int) error {
 		p.buffered.Flush()
 	}
 
-	if p.mediaControls != nil {
-		p.mediaControls.NotifySeek(targetSeconds)
-	}
-
-	// Report the landing position immediately rather than leaving the
-	// UI to guess until the next tick — this is the half of H-3 that
-	// desynced the seek bar by 30 s over four keyboard seeks.
-	p.emitPositionLocked()
-
 	return nil
 }
 
@@ -1140,6 +1271,10 @@ func (p *Player) seekerLengthSecsLocked() (int, error) {
 		return 0, errNoAudioFileLoaded
 	}
 
+	// Len is fixed for the life of the decoder, so unlike Position it
+	// races with nothing and needs no source lock -- which it must not
+	// take anyway: displayPositionSecsLocked calls this while holding
+	// it, and srcMu is not reentrant.
 	speaker.Lock()
 	length := p.seeker.Len() / int(p.format.SampleRate)
 	speaker.Unlock()
@@ -1156,6 +1291,8 @@ func (p *Player) displayPositionSecsLocked() int {
 		return 0
 	}
 
+	defer p.lockSourceLocked()()
+
 	speaker.Lock()
 	pos := p.seeker.Position()
 	total := p.seeker.Len()

backend/queue/fallback_test.go

@@ -83,7 +83,7 @@ func TestFallback_TriggersOnNaturalFinish(t *testing.T) {
 	q.SetFallbackSource(fake)
 
 	q.SetQueue(seedPaths, 0, false, Source{Type: "album", ID: 1, Label: "Seed Album"})
-	q.OnPlaybackFinished()
+	q.OnPlaybackFinished(nil)
 
 	waitUntil(t, func() bool { return fake.callCount() == 1 }, "fallback to be resolved")
 	waitUntil(t, func() bool {
@@ -159,7 +159,7 @@ func TestFallback_EmptyResultLeavesQueueExhausted(t *testing.T) {
 	q.SetFallbackSource(fake)
 
 	q.SetQueue(seedPaths, 0, false, Source{})
-	q.OnPlaybackFinished()
+	q.OnPlaybackFinished(nil)
 
 	waitUntil(t, func() bool { return fake.callCount() == 1 }, "fallback to be resolved")
 
@@ -193,7 +193,7 @@ func TestFallback_StaleResolutionDiscarded(t *testing.T) {
 	q.SetFallbackSource(fake)
 
 	q.SetQueue(seedPaths, 0, false, Source{})
-	q.OnPlaybackFinished() // starts resolving, blocked on gate
+	q.OnPlaybackFinished(nil) // starts resolving, blocked on gate
 
 	time.Sleep(20 * time.Millisecond) // let the goroutine reach the gate
 

backend/queue/finished_test.go

@@ -0,0 +1,78 @@
+package queue
+
+import (
+	"errors"
+	"testing"
+
+	"yellowjacket/backend/events"
+)
+
+// errTestDecode stands in for a decoder blowing up mid-track.
+var errTestDecode = errors.New("decode blew up")
+
+// currentIndex == -1 against a non-empty queue is a state this
+// package produces on purpose: onQueueExhausted(false) sets it and
+// deliberately leaves the finished track loaded in the player, so it
+// stays on the now-playing bar. Pressing play from there and letting
+// it finish re-enters OnPlaybackFinished with exactly that pair --
+// which used to index q.tracks[-1] and panic, on a goroutine
+// dispatched from the audio callback with no caller to recover it.
+func TestFinishedWithNoCurrentTrackDoesNotPanic(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name  string
+		index int
+	}{
+		{"exhausted queue leaves -1", -1},
+		{"index past the end", 3},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			q, _, _ := setupRecordedQueue(t)
+			q.tracks = []Track{
+				{FilePath: "/a.mp3"},
+				{FilePath: "/b.mp3"},
+			}
+			q.currentIndex = tt.index
+
+			// The assertion is that this returns at all.
+			q.OnPlaybackFinished(nil)
+
+			if q.currentIndex != tt.index {
+				t.Errorf(
+					"an out-of-range index was acted on: %d became %d",
+					tt.index, q.currentIndex,
+				)
+			}
+		})
+	}
+}
+
+// A track that broke mid-playback is not a track that was listened
+// to. The player cannot say so itself -- the metadata is here -- so
+// it hands the reason over and this is where it becomes a
+// PlaybackFailed rather than a silent auto-advance.
+func TestAFailedTrackIsReportedAndNotCountedAsAPlay(t *testing.T) {
+	t.Parallel()
+
+	q, _, rec := setupRecordedQueue(t)
+	q.tracks = []Track{
+		{FilePath: "/a.mp3", Title: "A", AudioFileID: 1},
+		{FilePath: "/b.mp3", Title: "B", AudioFileID: 2},
+	}
+	q.currentIndex = 0
+
+	q.OnPlaybackFinished(errTestDecode)
+
+	if _, ok := rec.Last(events.PlaybackFailed); !ok {
+		t.Errorf(
+			"a track that failed mid-playback told the user nothing; "+
+				"got %v",
+			rec.Names(),
+		)
+	}
+}

backend/queue/handlers.go

@@ -1,18 +1,45 @@
 package queue
 
-// OnPlaybackFinished is called when a track finishes playing naturally.
-// This drives the auto-advance behavior and records the play.
-func (q *Queue) OnPlaybackFinished() {
+// OnPlaybackFinished is called when a track stops streaming. This
+// drives the auto-advance behavior and records the play.
+//
+// srcErr says why the track stopped: nil for one that reached its
+// end, non-nil for one that broke partway through.  The player cannot
+// tell the user which, because the metadata lives here -- so a failure
+// is reported as PlaybackFailed and *not* recorded as a play, while
+// the advance happens either way.  Before this, a file that failed
+// mid-track advanced in silence and was counted as listened to.
+//
+//wails:ignore // internal wiring, not part of the app's IPC surface.
+func (q *Queue) OnPlaybackFinished(srcErr error) {
 	q.mu.Lock()
 
-	if len(q.tracks) == 0 {
+	// currentIndex is -1 whenever the queue has been exhausted, and
+	// onQueueExhausted deliberately leaves the finished track loaded
+	// in the player -- so a natural finish can re-enter here against a
+	// queue that is not empty and an index that is not valid.  Every
+	// other path in this package bounds-checks before indexing; this
+	// one panicked, on a goroutine with no caller to recover it.
+	if q.currentIndex < 0 || q.currentIndex >= len(q.tracks) {
 		q.mu.Unlock()
 
 		return
 	}
 
 	// Capture the track that just finished before advancing.
-	finishedID := q.tracks[q.currentIndex].AudioFileID
+	finished := q.tracks[q.currentIndex]
+	finishedID := finished.AudioFileID
+
+	if srcErr != nil {
+		q.emitPlaybackFailed(finished, srcErr)
+	}
+
+	// A track that broke was not listened to.
+	recordFinished := func() {
+		if srcErr == nil {
+			q.recordPlay(finishedID)
+		}
+	}
 
 	// Repeat One: replay the current track.
 	if q.repeatMode == RepeatOne {
@@ -21,7 +48,7 @@ func (q *Queue) OnPlaybackFinished() {
 		}
 
 		q.mu.Unlock()
-		q.recordPlay(finishedID)
+		recordFinished()
 
 		return
 	}
@@ -31,7 +58,7 @@ func (q *Queue) OnPlaybackFinished() {
 		// Queue exhausted — this is the extension point for a future fallback playlist.
 		q.onQueueExhausted(false)
 		q.mu.Unlock()
-		q.recordPlay(finishedID)
+		recordFinished()
 
 		return
 	}
@@ -44,12 +71,12 @@ func (q *Queue) OnPlaybackFinished() {
 	if !q.playCurrentOrSkip(true, q.nextIndex) {
 		q.onQueueExhausted(false)
 		q.mu.Unlock()
-		q.recordPlay(finishedID)
+		recordFinished()
 
 		return
 	}
 
 	q.emitIndexChanged()
 	q.mu.Unlock()
-	q.recordPlay(finishedID)
+	recordFinished()
 }

backend/queue/playbackfailed_test.go

@@ -107,7 +107,7 @@ func TestPlaybackFailed_AutoAdvanceSkipsPastIt(t *testing.T) {
 
 	// The first track finished: auto-advance lands on the missing
 	// file and must step over it rather than stopping dead.
-	q.OnPlaybackFinished()
+	q.OnPlaybackFinished(nil)
 
 	if got := q.GetState().CurrentIndex; got != 2 {
 		t.Errorf("currentIndex after skipping: got %d, want 2", got)
@@ -183,7 +183,7 @@ func TestQueueExhausted_KeepsTheFinishedTrackLoaded(t *testing.T) {
 
 	q.SetQueue(paths, 0, false, Source{})
 	q.Play()
-	q.OnPlaybackFinished()
+	q.OnPlaybackFinished(nil)
 
 	if q.GetState().CurrentIndex != -1 {
 		t.Errorf(

e2e/specs/album-dropdown.spec.ts

@@ -1,6 +1,12 @@
 import { test, expect } from '../support/fixtures.js';
 import type { Page } from '@playwright/test';
 
+/**
+ * How far the scroll test scrolls. One constant, because the guard and
+ * the assertion have to agree about it — they did not, which is #133.
+ */
+const SCROLL_TARGET = 80;
+
 /**
  * Plan 007 phase 5: expanding an album shows its tracks.
  *
@@ -104,20 +110,27 @@ test.describe('the album dropdown', () => {
     await app.setViewportSize({ width: 900, height: 600 });
 
     try {
-      await expect.poll(() => scrollRange(app)).toMatchObject({
-        scrollable: true,
-        overflowY: 'auto',
-      });
+      // Wait for the range the assertion below actually needs, not for
+      // "scrollable at all" (#133). The guard used to be
+      // `scrollHeight > clientHeight + 40` while the next line asks to
+      // reach 80, so any range in 41-79 satisfied it and could not
+      // satisfy the assertion — and the grid passes through exactly
+      // that while it settles, because it recomputes its columns after
+      // the resize rather than during it. The settled range here is
+      // 330, so this waits rather than weakening anything.
+      await expect
+        .poll(() => scrollRange(app))
+        .toMatchObject({ room: true, overflowY: 'auto' });
 
-      await app.evaluate(() => {
+      await app.evaluate((target) => {
         const sc = document
           .querySelector('cover-grid')
           ?.shadowRoot?.querySelector('.grid-scroll-container');
 
-        if (sc) sc.scrollTop = 80;
-      });
+        if (sc) sc.scrollTop = target;
+      }, SCROLL_TARGET);
 
-      expect(await scrollTop(app)).toBe(80);
+      expect(await scrollTop(app)).toBe(SCROLL_TARGET);
 
       // And the dropdown it opens is on screen, wherever the manager
       // decides that leaves the scroll. It is *not* "the position is
@@ -250,16 +263,19 @@ async function closeDropdown(app: Page): Promise<void> {
 
 /** Whether the grid can scroll at all, which decides if a probe can move. */
 async function scrollRange(app: Page) {
-  return app.evaluate(() => {
+  return app.evaluate((target) => {
     const sc = document
       .querySelector('cover-grid')
       ?.shadowRoot?.querySelector('.grid-scroll-container');
 
     return {
-      scrollable: !!sc && sc.scrollHeight > sc.clientHeight + 40,
+      // `room` is the precondition of the assertion that follows it:
+      // enough range to actually reach the target. A threshold below
+      // what the caller depends on is not a guard.
+      room: !!sc && sc.scrollHeight - sc.clientHeight >= target,
       overflowY: sc ? getComputedStyle(sc).overflowY : '',
     };
-  });
+  }, SCROLL_TARGET);
 }
 
 async function scrollTop(app: Page): Promise<number> {

e2e/specs/layout-overflow.spec.ts

@@ -26,6 +26,12 @@ const MIN_VIEWPORT = { width: 800, height: 600 };
 const VIEWPORTS = [
   { name: '1440×900', width: 1440, height: 900 },
   { name: '1024×768', width: 1024, height: 768 },
+  // Not the minimum, and that is the point (#24). The sidebar collapses
+  // to icons *below* 900, so the main panel is 843px at 899 and 700px
+  // at 900 — the narrowest content area any desktop width produces is
+  // here, not at the enforced floor. A list that stopped at the minimum
+  // was missing its own worst case.
+  { name: '900×600 (the widest sidebar, so the narrowest content)', width: 900, height: 600 },
   { name: `the minimum (${MIN_VIEWPORT.width}×${MIN_VIEWPORT.height})`, ...MIN_VIEWPORT },
 ];
 

e2e/specs/queue-overlay.spec.ts

@@ -0,0 +1,187 @@
+import { test, expect } from '../support/fixtures.js';
+
+/**
+ * #24 — the queue panel does not take the page's width away from it.
+ *
+ * The panel is `flex-shrink: 0` in the flow of `.content-area`, so an
+ * open queue used to be paid for by the main panel. Measured on
+ * Playlists before the fix:
+ *
+ * | viewport | main panel |
+ * |---|---|
+ * | 900×600 | 379px — all three header actions clipped |
+ * | 390×780 | 69px |
+ * | 320×600 | **0px** |
+ *
+ * **900×600 is the worst desktop case, not the 800×600 minimum**, and
+ * that is the trap this file exists to keep closed: the sidebar
+ * collapses to icons *below* 900, so the main panel is 843px at 899 and
+ * 700px at 900. A spec that checks "the minimum" and stops has not
+ * checked the worst case — which is what every viewport list in this
+ * suite did before this.
+ *
+ * These assert the *content's* width rather than the panel's mode
+ * wherever they can, because the mode is the mechanism and the width is
+ * the complaint.
+ */
+
+/** The bands from plan 018's size matrix, plus the pixel above the collapse. */
+const BANDS = [
+  { name: 'a wide desktop (1280×800)', width: 1280, height: 800, inline: true },
+  { name: 'the default window (1100×720)', width: 1100, height: 720, inline: true },
+  { name: 'a laptop (1024×768)', width: 1024, height: 768, inline: true },
+  { name: 'the worst desktop width (900×600)', width: 900, height: 600, inline: false },
+  { name: 'the enforced minimum (800×600)', width: 800, height: 600, inline: false },
+  { name: 'a phone (390×780)', width: 390, height: 780, inline: false },
+  { name: '400% zoom (320×600)', width: 320, height: 600, inline: false },
+];
+
+/**
+ * How much room the content has, and whether the shell needs scrolling
+ * to reach any of itself.
+ */
+const shellGeometry = (page: import('@playwright/test').Page) =>
+  page.evaluate(() => {
+    const main = document.querySelector('#main-content')!.getBoundingClientRect();
+    const panel = document.querySelector('#queue-panel')!;
+
+    return {
+      mainWidth: Math.round(main.width),
+      overlay: panel.hasAttribute('overlay'),
+      open: panel.hasAttribute('open'),
+      bodyScrollWidth: document.body.scrollWidth,
+      bodyClientWidth: document.body.clientWidth,
+    };
+  });
+
+async function openQueue(page: import('@playwright/test').Page) {
+  const toggle = page.locator('#queue-button');
+
+  if ((await toggle.getAttribute('aria-expanded')) !== 'true') {
+    await toggle.click();
+  }
+
+  await expect(toggle).toHaveAttribute('aria-expanded', 'true');
+}
+
+test.describe('an open queue leaves the content its width', () => {
+  for (const band of BANDS) {
+    test(`at ${band.name}`, async ({ app }) => {
+      await app.setViewportSize({ width: band.width, height: band.height });
+      await openQueue(app);
+
+      // The mode is settled by a ResizeObserver, so poll rather than
+      // read once: a single read races the resize and reports the
+      // previous viewport's answer.
+      await expect
+        .poll(async () => (await shellGeometry(app)).overlay)
+        .toBe(!band.inline);
+
+      const geo = await shellGeometry(app);
+
+      // The floor is the point of the whole issue. Inline, the queue is
+      // affordable and the content keeps the rest; as an overlay the
+      // content keeps *everything*, which is what makes 0px at 320
+      // impossible rather than merely unlikely.
+      expect(geo.mainWidth).toBeGreaterThanOrEqual(320);
+
+      if (!band.inline) {
+        expect(geo.mainWidth).toBeGreaterThanOrEqual(
+          Math.min(band.width, 320),
+        );
+      }
+
+      // And opening the queue must not make the shell overflow.
+      expect(geo.bodyScrollWidth).toBeLessThanOrEqual(geo.bodyClientWidth);
+    });
+  }
+});
+
+test.describe('an overlaid queue says it is over the content', () => {
+  test.beforeEach(async ({ app }) => {
+    await app.setViewportSize({ width: 900, height: 600 });
+  });
+
+  test('draws a scrim and closes when it is clicked', async ({ app }) => {
+    await openQueue(app);
+
+    const panel = app.locator('#queue-panel');
+
+    await expect(panel).toHaveAttribute('overlay', '');
+
+    // The scrim is `aria-hidden` on purpose — it is a dismissal target,
+    // and the named routes out are the close button and Escape — so it
+    // is located structurally rather than by role.
+    await panel.evaluate((el) =>
+      el.shadowRoot!.querySelector<HTMLElement>('.scrim')!.click(),
+    );
+
+    await expect(app.locator('#queue-button')).toHaveAttribute(
+      'aria-expanded',
+      'false',
+    );
+  });
+
+  /**
+   * `getByRole`, not a shadow-root query: this repo has shipped a
+   * nameless control three times, and a drawer with a scrim is exactly
+   * the shape that grows a fourth.
+   */
+  test('offers a named close button', async ({ app }) => {
+    await openQueue(app);
+
+    const close = app.getByRole('button', { name: 'Close queue' });
+
+    await expect(close).toBeVisible();
+    await close.click();
+
+    await expect(app.locator('#queue-button')).toHaveAttribute(
+      'aria-expanded',
+      'false',
+    );
+  });
+
+  test('closes on Escape and gives focus back to the toggle', async ({
+    app,
+  }) => {
+    const toggle = app.locator('#queue-button');
+
+    await toggle.focus();
+    await toggle.click();
+    await expect(toggle).toHaveAttribute('aria-expanded', 'true');
+
+    await app.keyboard.press('Escape');
+
+    await expect(toggle).toHaveAttribute('aria-expanded', 'false');
+    await expect(toggle).toBeFocused();
+  });
+});
+
+/**
+ * The inline panel is the mode that already worked, and the one every
+ * other queue spec is written against. It keeps its resize handle and
+ * gains none of the overlay's chrome.
+ */
+test.describe('a wide window keeps the queue beside the content', () => {
+  test('no scrim, no close button, and the content is narrower', async ({
+    app,
+  }) => {
+    await app.setViewportSize({ width: 1280, height: 800 });
+
+    const widthWithoutQueue = (await shellGeometry(app)).mainWidth;
+
+    await openQueue(app);
+
+    await expect(app.locator('#queue-panel')).not.toHaveAttribute(
+      'overlay',
+      '',
+    );
+
+    const geo = await shellGeometry(app);
+
+    expect(geo.mainWidth).toBeLessThan(widthWithoutQueue);
+    await expect(
+      app.getByRole('button', { name: 'Close queue' }),
+    ).toHaveCount(0);
+  });
+});

frontend/bindings/yellowjacket/backend/queue/queue.ts

@@ -113,14 +113,6 @@ export function Next(): $CancellablePromise<void> {
     return $Call.ByID(1968784044);
 }
 
-/**
- * OnPlaybackFinished is called when a track finishes playing naturally.
- * This drives the auto-advance behavior and records the play.
- */
-export function OnPlaybackFinished(): $CancellablePromise<void> {
-    return $Call.ByID(2184869763);
-}
-
 /**
  * Play handles a play request by either resuming the current track or
  * starting playback from the beginning of the queue. When a track is

frontend/index.css

@@ -231,6 +231,14 @@ body div.sidebar {
     display: flex;
     overflow: hidden;
     contain: layout style;
+
+    /* The containing block for the queue panel's overlay mode (plan
+       018, #24), which spans this box rather than taking width from
+       the main panel beside it. `contain: layout` already establishes
+       one; this says so on purpose, so that removing the containment
+       for a paint reason does not silently reparent the overlay to the
+       viewport. */
+    position: relative;
 }
 
 .main-panel {

frontend/src/components/queue-panel/queue-panel.ts

@@ -72,6 +72,24 @@ const MIN_WIDTH = 200;
 const MAX_WIDTH = 500;
 const DEFAULT_WIDTH = 320;
 
+/**
+ * The narrowest main panel the queue is allowed to leave behind before
+ * it stops being a column and becomes an overlay (plan 018, issue #24).
+ *
+ * There is no cliff to derive this from, and pretending otherwise would
+ * be the more dishonest answer: the track list rescales its columns
+ * continuously (213px down to 124px between main widths of 900 and 544,
+ * with no row overflow at any of them) and the album grid steps 3
+ * columns to 2 without breaking. So this is a judgement, anchored at
+ * both ends — it keeps the *default* 1100px window inline, because an
+ * inline queue is a desktop affordance people choose and demoting the
+ * common case to an overlay would be a regression in feel; and it puts
+ * every case measured as broken on the overlay side, which is 900x600
+ * (main = 379px, where all three of the Playlists header's actions are
+ * clipped) and every phone width (main = 69px at 390, 0px at 320).
+ */
+const MAIN_PANEL_FLOOR = 480;
+
 @customElement('queue-panel')
 export class QueuePanel
     extends LitElement
@@ -85,6 +103,22 @@ export class QueuePanel
     @property({ type: Boolean, reflect: true })
     open = false;
 
+    /**
+     * Whether the panel is covering the content instead of sitting
+     * beside it. **Computed, never set by a caller** — it is reflected
+     * so the stylesheet and a spec can both read it.
+     *
+     * It is deliberately *not* a media query, which is the whole reason
+     * this is a property and not a `@media` block. The panel's width is
+     * user state: drag-resizable between MIN_WIDTH and MAX_WIDTH and
+     * persisted. A breakpoint at a fixed viewport width silently
+     * assumes the default 320, so it is wrong by up to 180px for a user
+     * who has widened the panel — in the direction that hurts, since a
+     * wider queue is exactly when the content can least afford it.
+     */
+    @property({ type: Boolean, reflect: true })
+    overlay = false;
+
     @state()
     private isDragging = false;
 
@@ -190,6 +224,19 @@ export class QueuePanel
     private panelWidth = DEFAULT_WIDTH;
     private scrollbarDragging = false;
 
+    /** Watches `.content-area`, which is the viewport minus the sidebar. */
+    private spaceObserver?: ResizeObserver;
+
+    /**
+     * What had focus when the overlay opened, so Escape and the scrim
+     * can give it back. Focus is only taken back if the panel had it —
+     * the same rule `MenuKeyboard` follows, for the same reason: the
+     * queue can also be closed by the button in the bottom bar, and
+     * yanking focus away from wherever the user actually is would be
+     * worse than leaving it.
+     */
+    private overlayOpener: HTMLElement | null = null;
+
     // _itemSize is an internal property applied via Object.assign in BaseLayout's
     // config setter. Setting it to match the actual fixed .track-item height (49px)
     // prevents lit-virtualizer's scroll error correction from fighting the native
@@ -265,6 +312,86 @@ export class QueuePanel
             border-left: 1px solid var(--yj-border-subtle, #333);
         }
 
+        /* ---------------------------------------------------------
+           Overlay mode (plan 018, #24).
+
+           In flow the panel takes its width *from the main panel*,
+           which is the reported bug: at 900x600 that left 379px and
+           clipped every action in the Playlists header, and at 320px
+           it left 0px — the content was not degraded but gone.
+
+           Here the host spans the whole content area instead and
+           stops being a layout participant, so the main panel keeps
+           its full width and the queue sits over it. The host itself
+           is transparent and click-through; the scrim and the panel
+           are what take pointer events. The containment drops paint,
+           which would otherwise clip the panel's own shadow.
+           --------------------------------------------------------- */
+        :host([overlay]) {
+            position: absolute;
+            inset: 0;
+            width: auto;
+            background-color: transparent;
+            overflow: visible;
+            pointer-events: none;
+            contain: layout style;
+            z-index: 20;
+        }
+
+        /* Closed, an overlay is not there at all. In flow the panel is
+           width: 0, which is its own way of saying this; absolutely
+           positioned there is no width to collapse. */
+        :host([overlay]:not([open])) {
+            display: none;
+        }
+
+        :host([overlay][open]) {
+            border-left: none;
+        }
+
+        :host([overlay]) .panel-content {
+            position: absolute;
+            top: 0;
+            right: 0;
+            bottom: 0;
+            width: var(--queue-width, ${unsafeCSS(DEFAULT_WIDTH)}px);
+            max-width: 100%;
+            box-sizing: border-box;
+            background-color: var(--yj-bg-surface, #212529);
+            border-left: 1px solid var(--yj-border-subtle, #333);
+            box-shadow: -8px 0 24px rgb(0 0 0 / 45%);
+            pointer-events: auto;
+        }
+
+        /* Dragging the edge of something that is already covering the
+           content answers a question nobody asked, and it is a
+           mouse-only affordance either way. */
+        :host([overlay]) .resize-handle {
+            display: none;
+        }
+
+        .scrim {
+            position: absolute;
+            inset: 0;
+            background-color: rgb(0 0 0 / 45%);
+            pointer-events: auto;
+            border: none;
+            padding: 0;
+            margin: 0;
+            cursor: pointer;
+        }
+
+        /* The phone gets the whole width: below 600 there is no
+           "beside" left to be, and this is the shape #55 turns into a
+           real screen. A media query inside a shadow root is answered
+           by the viewport, so the component states this itself rather
+           than the shell reaching in. */
+        @media (max-width: 599px) {
+            :host([overlay]) .panel-content {
+                width: 100%;
+            }
+        }
+
         .resize-handle {
             position: absolute;
             top: 0;
@@ -656,6 +783,20 @@ export class QueuePanel
             '--queue-width',
             `${this.panelWidth}px`,
         );
+
+        // The mode is a measurement, so it is observed rather than
+        // computed once: the parent is `.content-area`, whose width is
+        // the viewport minus the sidebar — including the sidebar's own
+        // collapse at 900px, which is what makes 900 the *worst*
+        // desktop width rather than the minimum.
+        this.updateOverlayMode();
+
+        if (this.parentElement) {
+            this.spaceObserver = new ResizeObserver(() =>
+                this.updateOverlayMode(),
+            );
+            this.spaceObserver.observe(this.parentElement);
+        }
         document.addEventListener(
             'mousemove',
             this.handleMouseMove,
@@ -690,6 +831,9 @@ export class QueuePanel
         super.disconnectedCallback();
         this.creditsUnsub?.();
         this.creditsUnsub = undefined;
+        this.spaceObserver?.disconnect();
+        this.spaceObserver = undefined;
+        document.removeEventListener('keydown', this.onOverlayKeydown);
         document.removeEventListener(
             'mousemove',
             this.handleMouseMove,
@@ -736,7 +880,79 @@ export class QueuePanel
         this.delegationAttached = false;
     }
 
+    /**
+     * Decide whether the queue can afford to be a column.
+     *
+     * The parent is `.content-area`, so its width is the viewport minus
+     * the sidebar and the sum already accounts for the sidebar's own
+     * collapse. It is stable across the panel's own open/closed state
+     * in both modes — in flow the panel is a child of that box, and as
+     * an overlay it is out of flow — so this cannot oscillate.
+     */
+    private updateOverlayMode = () => {
+        const available = this.parentElement?.clientWidth ?? 0;
+
+        // Before layout there is nothing to measure, and answering 0 by
+        // flipping to overlay would show the scrim for a frame.
+        if (available === 0) return;
+
+        this.overlay = available - this.panelWidth < MAIN_PANEL_FLOOR;
+    };
+
+    /**
+     * Escape closes a scrimmed overlay, which is the one keyboard rule
+     * every dialog in this app already follows.
+     *
+     * It is a document listener rather than a panel-scoped binding
+     * (`services/shortcut-scope.ts`) because it is not a *shortcut*: it
+     * is the dismissal of something covering the page, and it has to
+     * work while focus is still behind the scrim. It is attached only
+     * while the overlay is actually up and removed on close, so it is
+     * scoped to a state rather than being a permanent global. Nothing
+     * else binds Escape — the shortcut service only uses it to blur a
+     * text input.
+     */
+    private onOverlayKeydown = (e: KeyboardEvent) => {
+        if (e.key !== 'Escape' || !this.open || !this.overlay) return;
+
+        e.stopPropagation();
+        this.closeFromOverlay();
+    };
+
+    private closeFromOverlay = () => {
+        const hadFocus = this.contains(
+            document.activeElement as Node | null,
+        );
+
+        this.open = false;
+
+        if (hadFocus) {
+            const back =
+                this.overlayOpener ??
+                document.getElementById('queue-button');
+
+            back?.focus();
+        }
+
+        this.overlayOpener = null;
+    };
+
     override updated() {
+        // The overlay owns Escape only while it is up.
+        if (this.open && this.overlay) {
+            document.addEventListener('keydown', this.onOverlayKeydown);
+
+            this.overlayOpener ??=
+                document.activeElement instanceof HTMLElement &&
+                document.activeElement !== document.body
+                    ? document.activeElement
+                    : null;
+        } else {
+            document.removeEventListener('keydown', this.onOverlayKeydown);
+
+            if (!this.open) this.overlayOpener = null;
+        }
+
         // Closed, the panel is `width: 0` — which hides it from the eye
         // and from nobody else: its Clear and Add buttons still took tab
         // stops at x=1440 and were still read out (H-5).  `inert` is the
@@ -1631,6 +1847,11 @@ export class QueuePanel
             '--queue-width',
             `${clampedWidth}px`,
         );
+
+        // Widening the panel is one of the two ways the content can run
+        // out of room, and it is the way a viewport-width media query
+        // cannot see at all.
+        this.updateOverlayMode();
     };
 
     private handleMouseUp = () => {
@@ -1714,6 +1935,15 @@ export class QueuePanel
         const tracks = this.queue.tracks;
 
         return html`
+            ${this.overlay
+                ? html`<div
+                      class="scrim"
+                      part="scrim"
+                      data-testid="queue-scrim"
+                      aria-hidden="true"
+                      @click=${this.closeFromOverlay}
+                  ></div>`
+                : nothing}
             <div class="panel-content">
                 <div
                     class="resize-handle ${this.isDragging
@@ -1763,6 +1993,16 @@ export class QueuePanel
                                 name=${ICON_PLAYLIST}
                             ></wa-icon>
                         </button>
+                        ${this.overlay
+                            ? html`<button
+                                  class="header-action-button"
+                                  data-testid="queue-close"
+                                  aria-label="Close queue"
+                                  @click=${this.closeFromOverlay}
+                              >
+                                  <wa-icon name="xmark"></wa-icon>
+                              </button>`
+                            : nothing}
                     </div>
                 </div>
 

frontend/test/components/queue-overlay-mode.test.ts

@@ -0,0 +1,175 @@
+/**
+ * #24 — the queue stops being a column when it cannot afford to be one.
+ *
+ * In flow the panel is `flex-shrink: 0`, so it takes its width *from
+ * the main panel* rather than covering it. Measured against the running
+ * app on the Playlists page, that left 379px of content at 900×600 —
+ * with all three of the page header's actions clipped — 69px at 390px
+ * wide, and **0px** at 320px, where the content was not degraded but
+ * gone.
+ *
+ * The rule is `available - panelWidth >= MAIN_PANEL_FLOOR`, and the
+ * reason it is a computed property rather than a `@media` block is the
+ * third test here: the panel's width is user state, drag-resizable
+ * between 200 and 500px and persisted, so a breakpoint on the viewport
+ * alone is wrong by up to 180px for a user who has widened it — in the
+ * direction that hurts, since a wider queue is exactly when the content
+ * can least afford it.
+ *
+ * The parent is `.content-area`, i.e. the viewport minus the sidebar,
+ * which is why these mount into a sized wrapper rather than into
+ * `document.body`: the width that decides this is the *parent's*, and
+ * `fixture()` would hand the panel the whole test window.
+ */
+import { describe, expect, it, afterEach } from 'vitest';
+
+import '@components/queue-panel/queue-panel';
+import type { QueuePanel } from '@components/queue-panel/queue-panel';
+import { shadow } from '@test/support/render';
+
+const wrappers: HTMLElement[] = [];
+
+afterEach(() => {
+  for (const w of wrappers.splice(0)) w.remove();
+});
+
+/**
+ * Mount a panel inside a parent of a stated width.
+ *
+ * The wrapper is `position: relative` and `display: flex` because that
+ * is what `.content-area` is; the mode is measured from
+ * `parentElement.clientWidth`, so a wrapper that collapses to its
+ * content would measure the panel rather than the space around it.
+ */
+async function panelIn(parentWidth: number): Promise<QueuePanel> {
+  const wrapper = document.createElement('div');
+
+  wrapper.style.cssText = `position: relative; display: flex; width: ${parentWidth}px;`;
+  document.body.append(wrapper);
+  wrappers.push(wrapper);
+
+  const el = document.createElement('queue-panel') as QueuePanel;
+
+  el.open = true;
+  wrapper.append(el);
+
+  await el.updateComplete;
+  await settle(el);
+
+  return el;
+}
+
+/**
+ * A ResizeObserver delivers on a frame, not a microtask, so the mode
+ * lands a frame after the width that decides it.
+ */
+async function settle(el: QueuePanel): Promise<void> {
+  for (let frame = 0; frame < 4; frame += 1) {
+    await new Promise((r) => {
+      requestAnimationFrame(() => r(null));
+    });
+    await el.updateComplete;
+  }
+}
+
+/** Drag the resize handle by `dx`, the way a user widens the panel. */
+async function dragHandleBy(el: QueuePanel, dx: number): Promise<void> {
+  const handle = shadow<HTMLElement>(el, '.resize-handle');
+  const startX = el.getBoundingClientRect().left;
+
+  if (!handle) throw new Error('no resize handle to drag');
+
+  handle.dispatchEvent(
+    new MouseEvent('mousedown', { clientX: startX, bubbles: true }),
+  );
+  document.dispatchEvent(
+    new MouseEvent('mousemove', { clientX: startX - dx, bubbles: true }),
+  );
+  document.dispatchEvent(new MouseEvent('mouseup', { bubbles: true }));
+
+  await settle(el);
+}
+
+describe('the queue panel decides whether it can be a column', () => {
+  it('stays inline while the content can spare the width', async () => {
+    const el = await panelIn(1080);
+
+    expect(el.overlay).toBe(false);
+    expect(el.hasAttribute('overlay')).toBe(false);
+  });
+
+  it('becomes an overlay when it cannot', async () => {
+    const el = await panelIn(700);
+
+    expect(el.overlay).toBe(true);
+    expect(el.hasAttribute('overlay')).toBe(true);
+  });
+
+  /**
+   * The test the media query could not have passed. The parent does not
+   * move; only the user's own panel width does.
+   */
+  it('flips to overlay when the user widens the panel, at a fixed width', async () => {
+    const el = await panelIn(880);
+
+    expect(el.overlay).toBe(false);
+
+    await dragHandleBy(el, 180);
+
+    expect(el.overlay).toBe(true);
+  });
+
+  it('gives an overlay a scrim and a named way out, and an inline panel neither', async () => {
+    const overlaid = await panelIn(700);
+
+    expect(shadow(overlaid, '.scrim')).toBeTruthy();
+
+    const close = shadow(overlaid, '[data-testid="queue-close"]');
+
+    expect(close?.getAttribute('aria-label')).toBe('Close queue');
+
+    const inline = await panelIn(1080);
+
+    expect(inline.shadowRoot?.querySelector('.scrim')).toBeNull();
+    expect(
+      inline.shadowRoot?.querySelector('[data-testid="queue-close"]'),
+    ).toBeNull();
+  });
+
+  it('closes on the scrim, on the close button and on Escape', async () => {
+    for (const close of [
+      (el: QueuePanel) => shadow<HTMLElement>(el, '.scrim')?.click(),
+      (el: QueuePanel) =>
+        shadow<HTMLElement>(el, '[data-testid="queue-close"]')?.click(),
+      () =>
+        document.dispatchEvent(
+          new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }),
+        ),
+    ]) {
+      const el = await panelIn(700);
+
+      expect(el.open).toBe(true);
+
+      close(el);
+      await el.updateComplete;
+
+      expect(el.open).toBe(false);
+    }
+  });
+
+  /**
+   * Escape belongs to the overlay, not to the queue. An inline panel is
+   * beside the content rather than over it, so there is nothing to
+   * dismiss and the key has to reach whatever else wants it.
+   */
+  it('leaves Escape alone while inline', async () => {
+    const el = await panelIn(1080);
+
+    document.dispatchEvent(
+      new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }),
+    );
+    await el.updateComplete;
+
+    expect(el.open).toBe(true);
+  });
+});

lefthook.yml

@@ -63,8 +63,17 @@ pre-commit:
       root: "frontend/"
       run: node scripts/check-css-literals.mjs
 
+# Deliberately sequential, unlike pre-commit.  `go test -race`
+# saturates every core for the better part of a minute and the UI tier
+# is a real browser with wall-clock timeouts, so run together the
+# browser loses: setup took 106s inside the hook against 63s
+# standalone, and a different suite failed each time -- three suites
+# failing to fetch setup.ts from Vitest's own dev server on one run, a
+# 15s "did not mount itself" on the next, against a suite that passes
+# 898/898 on its own. A gate that fails at random is not a gate. The
+# ~15s saved is not worth it.
 pre-push:
-  parallel: true
+  parallel: false
   commands:
     go-test:
       glob: "*.go"

scripts/dev-headless.sh

@@ -97,6 +97,55 @@ if [ -f "$PID_FILE" ] && kill -0 "$(cat "$PID_FILE")" 2>/dev/null; then
 fi
 rm -f "$PID_FILE"
 
+# ── Refuse to inherit somebody else's port ───────────────────────────
+# The PID check above only knows about *this* worktree: `make dev-stop`
+# kills the pid in this .dev/app.pid and nothing else.  Several worktrees
+# of this repo share the default port, so an app orphaned by a deleted
+# worktree goes on listening with nothing left to stop it.
+#
+# Without this check the new app starts, fails to bind, exits — and every
+# curl and playwright-cli call afterwards goes to the *other* process, so
+# the harness reports facts about an app nobody asked for.  That is not a
+# quiet wrongness either: it presented as
+# "no such table: libraries" against a freshly created YJ_HOME, which
+# reads exactly like applySchema or staleshape.go having gone wrong and
+# is a frightening place to start looking.
+#
+# The startup wait below cannot catch it, because the health check is
+# satisfied by *any* app on the port — which is precisely the failure.
+# So it is refused here, before anything is launched, rather than warned
+# about.  --port already exists for the legitimate second-app case.
+port_holder() {
+	command -v ss >/dev/null || return 0
+	ss -lptn "sport = :$PORT" 2>/dev/null | grep -oP 'pid=\K[0-9]+' | head -n 1
+}
+
+if curl -sf -o /dev/null --max-time 2 "http://localhost:$PORT/" ||
+	[ -n "$(port_holder)" ]; then
+	holder="$(port_holder)"
+	echo "dev-headless: :$PORT is already in use; refusing to start" >&2
+	if [ -n "$holder" ]; then
+		# /proc/<pid>/cwd names the checkout it belongs to, and says
+		# "(deleted)" for the orphaned-worktree case that is the whole
+		# reason this is worth a check.
+		cwd="$(readlink "/proc/$holder/cwd" 2>/dev/null || echo unknown)"
+		cmd="$(tr '\0' ' ' <"/proc/$holder/cmdline" 2>/dev/null || echo unknown)"
+		echo "  pid  $holder  ($cmd)" >&2
+		echo "  cwd  $cwd" >&2
+		# The PID-file check above has already passed, so whatever this
+		# is, `make dev-stop` does not know about it — saying otherwise
+		# sends you to a command that will report success and change
+		# nothing.  Never `pkill -f` here either: the pattern would
+		# match this script's own command line.
+		echo "  'make dev-stop' will not touch it (it is not in" >&2
+		echo "  ${PID_FILE#"$REPO_ROOT"/}): kill $holder, or pass --port." >&2
+	else
+		echo "  The holder could not be identified (no ss, or it belongs" >&2
+		echo "  to another user). Try: ss -lptn 'sport = :$PORT'" >&2
+	fi
+	exit 1
+fi
+
 # ── Choose the YJ_HOME ───────────────────────────────────────────────
 # A seed is a YJ_HOME that a previous run of the app produced, tarred
 # up (see scripts/seed-sandbox.sh).  Restoring it means starting *in*
@@ -200,6 +249,20 @@ until curl -sf -o /dev/null "http://localhost:$PORT/"; do
 	sleep 0.25
 done
 
+# The loop above exits on the first answer from the port, and "something
+# answered" is not "the app we started answered".  The pre-launch guard
+# makes that unlikely rather than impossible — a race, or a listener
+# started in between — and the check is one signal, so it is worth making
+# here too.  An empty log beside a dead pid is the "it exited immediately
+# and nothing said so" case that the original report spent its time on.
+if ! kill -0 "$APP_PID" 2>/dev/null; then
+	echo "dev-headless: :$PORT answered, but the app we started (pid" >&2
+	echo "  $APP_PID) is gone — something else holds the port." >&2
+	tail -n 30 "$LOG_FILE" >&2
+	rm -f "$PID_FILE"
+	exit 1
+fi
+
 cat <<EOF
 dev-headless: up
   url      http://localhost:$PORT