docs(ui): quote the shipped fade's own measurement

The comment on `wa-dialog::part(body)` carried bottom-edge pixels from an intermediate probe (29,33,36) while `.planning/NOTES.md` recorded the final sample against the shipped rule (22,24,27) — the same gradient, read a few pixels higher up the box. A measurement written in two places has to agree, or neither can be trusted.
fix(ui): the phone's context sheet says when it scrolls
2026-08-23 07:04:04 -04:00 · 2026-08-23 06:45:46 -04:00
4 changed files with 162 additions and 2 deletions
@@ -4912,3 +4912,49 @@ bridge leaves the wizard up with its "Get Started" button correctly
 disabled — it gates on a directory chosen *in the wizard*, and the
 existing-library check runs once, on mount. A reload clears it. Nothing
 is broken; it cost twenty minutes of believing a tap had been swallowed.
+
+## The sheet's scroll fade, and where a scrim may not go (measured 2026-08-23, headless)
+
+#207's answer. The affordance is two background layers on
+`wa-dialog::part(body)` and the conditionality is
+`background-attachment`, not a scroll listener: a cover of the sheet's
+own colour painted at the end of the *content* (`local`) over a shadow
+pinned to the box (`scroll`), so the cover scrolls up and hides the
+shadow exactly when there is nothing more to see.
+
+Measured at 424x360 (which is where a menu overflows on `main`, since
+`main` does not yet carry #67's eighth item — at 424x439 the track
+list's seven items are `scrollHeight` 364 against `clientHeight` 364,
+fitting exactly). Pixel at x=300, dark ramp, `bgElevated` `#343a40`:
+
+| y | before | more below | at the end of the list |
+|---|---|---|---|
+| 330 | 52,58,64 | 50,56,62 | 52,58,64 |
+| 340 | 52,58,64 | 43,48,53 | 52,58,64 |
+| 350 | 52,58,64 | 33,37,40 | 52,58,64 |
+| 359 | 52,58,64 | 22,24,27 | 52,58,64 |
+
+Three things worth keeping.
+
+**A menu that fits draws nothing**, which is the same measurement: at
+424x439 the sheet is flat 52,58,64 to its bottom edge, because with no
+overflow the `local` layer's positioning area *is* the padding box and
+the cover lands on top of the shadow.
+
+**A scrim over a menu row is that row's text surface**, so the 4.5:1
+rule reaches it and this is why the curve is steep rather than linear.
+A row is 48px with its label centred; 32px of scrim already down to a
+quarter strength at 14px puts about 0.06 at the label. Checked on the
+light ramp (`bgElevated` `#e9ecef`, text `#212529`) by overriding the
+two custom properties on `:root`: background at the label 205,207,210,
+which is **9.9:1**. The first draft — a linear 48px at 0.8 — put ~0.375
+on that label, 5.0:1, passing but visibly greyed. The bottom few pixels
+go to ~2.4:1 in either draft and are deliberately below where any
+label of a *fully visible* row sits; a label that lands there belongs
+to the half-cut row, which is the thing being signalled.
+
+**A dark scrim on a dark surface reads far worse in a shrunk screenshot
+than on screen.** The first two probes (24px/0.45, then 32px/0.75) were
+measurably present — 52,58,64 down to 30,33,37 — and invisible in the
+inline preview. Crop the bottom 70px and scale it up before judging;
+the pixel values are the honest answer either way.
@@ -1402,7 +1402,7 @@ descendants. On the reference device the main panel spans 0-318 of a
 items cut off, with no way to reach them. `showModal()` is Chrome 37
 and uses the real top layer, so a dialog is immune by construction.

-Six things about it are load-bearing.
+Seven things about it are load-bearing.

 **"Dialogs are fine" needed checking, because every other dialog in
 this app is mounted in `index.html`** — outside `.main-panel` — so it
@@ -1431,6 +1431,25 @@ doing nothing, which reads as the gesture breaking. `menu-dismiss` is
 that signal; the three surfaces that do not use `ContextMenuController`
 bind it themselves.

+**A sheet that scrolls says so, and `background-attachment` is what
+asks whether it does** (#207). The sheet is capped at 85vh — a surface
+covering the whole screen is a page, not a sheet — so a long menu's
+body scrolls, and for three phases it scrolled *silently*: measured at
+424x439, eight items ended at y=470 with the fold at 439, and where the
+cut lands on a row boundary the sheet ends in a clean edge that reads
+as the end of the list. The fade is two background layers on
+`wa-dialog::part(body)` — a shadow pinned to the box (`scroll`) under a
+cover of the sheet's own colour painted at the end of the *content*
+(`local`), which scrolls up over the shadow exactly when there is
+nothing more to see. So it is absent on a menu that fits, present the
+moment one does not, and gone again at the end of the list, with no
+scroll listener and nothing reaching into `wa-dialog`'s shadow root for
+the scroller. **The curve is steep because the rows under it stay
+live**: a scrim over a menu item is that item's text surface, and the
+4.5:1 rule applies to it — 32px already down to a quarter strength at
+14px spends its weight below the last legible label, measured at 9.9:1
+on the light ramp, whose `bgElevated` is `#e9ecef`.
+
 **The playlist submenu is a sheet too, and it had to be.** It is a
 `placement="right-start"` flyout, and making the menu full-width moved
 its anchor — measured at x −182 to 0, entirely off-screen, so "Add to
@@ -155,10 +155,55 @@ export class MenuSurface extends LitElement {
           bottom was at y=452 on a 439px screen -- the one row a
           destructive action is most likely to be. The cap has to stay
           (a sheet covering the whole screen is a page, not a sheet),
-           so the body is what gives. */
+           so the body is what gives.
+
+           **And a body that scrolls says so** (#207). Scrolling was the
+           whole of the fix above, which left the last item reachable
+           and nothing on screen admitting it was there -- measured at
+           424x439, eight items ending at y=470 with the fold at 439,
+           and worse when the cut lands on a row boundary, where the
+           sheet ends in a clean edge that reads as the end of the list.
+
+           Two layers, and the *order* is what asks the question: a
+           shadow pinned to the bottom of the box (attachment scroll),
+           and over it a cover of the sheet's own colour painted at the
+           end of the *content* (attachment local), which therefore
+           scrolls up over the shadow and hides it exactly when there is
+           nothing more to see. So the affordance is absent on a menu
+           that fits, present the moment one does not, and gone again at
+           the end of the list -- with no scroll listener, no
+           measurement, and nothing reaching into wa-dialog's shadow
+           root for the scroller. background-attachment is Chrome 4;
+           the reference device is Chrome 113.
+
+           **The curve is steep because the rows under it stay live.**
+           A scrim over a menu item is that item's text surface, and
+           this app's rule is that text clears 4.5:1 on every surface it
+           can sit on -- which the light ramp, whose bgElevated is
+           #e9ecef, is what makes non-theoretical. A row is 48px with
+           its label centred, so 32px of scrim that is already down to
+           a quarter strength at 14px reaches y-centre at about 0.06 and
+           spends its weight on the strip below the last legible label.
+           Measured on the dark ramp at x=300, flat 52,58,64 throughout
+           before: 50,56,62 at y=330, 33,37,40 at y=350 and 22,24,27 at
+           the bottom edge, and flat again at the end of the list. The
+           light ramp puts 9.9:1 on the last label. */
        wa-dialog::part(body) {
            padding: 0;
            overflow-y: auto;
+            background:
+                linear-gradient(
+                        var(--yj-bg-elevated, #343a40),
+                        var(--yj-bg-elevated, #343a40)
+                    )
+                    bottom / 100% 32px no-repeat local,
+                linear-gradient(
+                        to top,
+                        rgba(0, 0, 0, 0.6) 0%,
+                        rgba(0, 0, 0, 0.25) 45%,
+                        rgba(0, 0, 0, 0) 100%
+                    )
+                    bottom / 100% 32px no-repeat scroll;
        }

        /* A sheet is dragged at with a thumb, so it says where its top
@@ -206,6 +206,56 @@ describe('menu-surface', () => {
      expect(dismissed, 'no menu-dismiss reached the document').toBe(1);
    });

+    /**
+     * The scroll affordance (#207), and this is the mechanism again
+     * rather than the symptom.
+     *
+     * The sheet's body has scrolled since #60 and said nothing about
+     * it: measured at 424x439, eight items ended at y=470 with the
+     * fold at 439, and where the cut lands on a row boundary the sheet
+     * ends in a clean edge that reads as the end of the list.
+     *
+     * What makes the fade *conditional* — absent on a menu that fits,
+     * present the moment one does not, gone again at the end of the
+     * list — is `background-attachment`, not a scroll listener: a cover
+     * of the sheet's own colour is painted at the end of the content
+     * and attached `local`, over a shadow pinned to the box and
+     * attached `scroll`. So the pair of attachments *is* the feature,
+     * and it is what this asserts. The rendered result was measured in
+     * the harness (dark ramp 52,58,64 flat before; 52,57,63 at the last
+     * label and 22,24,27 at the bottom edge with more below; flat again
+     * at the end of the list) and is on the PR.
+     */
+    it('paints the fade only while there is more below', async () => {
+      const el = await surfaceWithPanel();
+
+      const wrapper = el.shadowRoot?.querySelector('wa-dialog');
+
+      await (wrapper as HTMLElement & { updateComplete: Promise<unknown> })
+        .updateComplete;
+
+      const body = wrapper?.shadowRoot?.querySelector('[part~="body"]');
+
+      expect(body, 'no body part to scroll').not.toBeNull();
+
+      const style = getComputedStyle(body as Element);
+
+      expect(style.overflowY, 'the body is what gives, not the cap').toBe(
+        'auto',
+      );
+
+      // The cover scrolls with the content; the shadow does not. Either
+      // one alone is a fade that is always there or never there.
+      expect(
+        style.backgroundAttachment,
+        'the cover must be local and the shadow must not',
+      ).toBe('local, scroll');
+
+      // Both sit at the bottom, or the cover hides nothing.
+      expect(style.backgroundPosition).toBe('50% 100%, 50% 100%');
+      expect(style.backgroundSize).toBe('100% 32px, 100% 32px');
+    });
+
    /**
     * A dialog with no accessible name is what `utils/name-dialog.ts`
     * exists for; here the name is already written on the panel, so no