gui: after the outside review of #116 - two guards bounded from both sides, the tip's shade in the palette

Three findings, all three true on the code as it stood:

- the fold head's fill was asked to be narrower than its row and wider
  than nothing, which a one pixel fill satisfies. It is now asked to be at
  least as wide as the title it lights and narrower than the row;
- the pairing of a name with the box under it was measured once, between
  the first two fields, and applied to every field - a later pair could
  drift while the first still held. Each name is now measured against the
  next name down the screen;
- the shade under an explanation was a colour written at the call site.
  It is a name of the palette now, in both variants - its own name rather
  than the toolkit's Shadow, which this palette answers with nothing on
  purpose since 2026-08-24.

Run: the guards of the touched files and the cheap whole-tree gates (41),
gofmt, vet, lint, staticcheck.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: donislawdev

internal/guard/foldhead_test.go

@@ -202,8 +202,17 @@ func TestTheHeadRowDrawsItsStatesAndTheArrowFollows(t *testing.T) {
 	// form, which is enormous. The row is still the target - the head is as
 	// wide as the row - so the two widths are asked for apart: the head wide,
 	// its fill narrow.
-	if row, fill := head.Size().Width, back.Size().Width; fill >= row || fill < 1 {
-		t.Errorf("under the pointer the fill is %.0f px wide on a head %.0f px wide - the fill has to cover the words and not the row", fill, row)
+	// Bounded from both sides, after the outside review of #116: "narrower
+	// than the row" alone would have let a one pixel fill through. The fill
+	// has to be at least as wide as the title it lights, and narrower than
+	// the row it stands in.
+	title, ok := labelBox(fold.Object(), "Notes for the manifest")
+	if !ok {
+		t.Fatal("the fold's title is not on the screen, so there is nothing to measure the fill against")
+	}
+	if row, fill := head.Size().Width, back.Size().Width; fill >= row || fill < title.Width {
+		t.Errorf("under the pointer the fill is %.0f px wide, the title %.0f and the head %.0f - the fill has to cover the words and stop short of the row",
+			fill, title.Width, row)
 	}
 	if arrow.Resource.Name() == restingArrow {
 		t.Error("the arrow is inked the same under the pointer as at rest, so it does not follow the row")

internal/guard/guitext_test.go

@@ -109,6 +109,7 @@ var notWords = map[string]string{
 	`"•"`:             "the marker in front of a list item, a shape rather than a word",
 	`"panel"`:         "our name for a colour, in the palette the toolkit asks by name",
 	`"label"`:         "our name for the ink of a field's name, a colour the palette holds",
+	`"tipshade"`:      "our name for the shade under an explanation, a colour the palette holds",
 	`"lift"`:          "our name for what the pointer does to the filled button, a colour the palette holds",
 	`"shade"`:         "our name for what a press does to the filled button, a colour the palette holds",
 	`"fyneDo"`:        "a migration flag the toolkit reads, never shown",

internal/guard/spacingscale_test.go

@@ -72,13 +72,14 @@ func TestANameStandsOverItsBoxOnOneEdgeWithEveryOther(t *testing.T) {
 		}
 	}
 	// The pairing: a name is nearer the box under it than that box is to the
-	// next name. Asked between neighbours inside one section, because a
-	// section's edge is a bigger gap for a reason of its own.
-	between := gapBelowField(t, generate, text.FieldFormat(), text.FieldSize())
-	for i, gap := range nameGaps {
-		if gap >= between {
-			t.Errorf("%q stands %.1f px over its box and the next name stands %.1f px under it, so nothing says which box the name belongs to",
-				names[i], gap, between)
+	// next name. Asked for each pair down the screen rather than once at the
+	// top, after the outside review of #116: measured once, a later pair
+	// could drift while the first still held.
+	for i := 0; i+1 < len(names); i++ {
+		between := gapBelowField(t, generate, names[i], names[i+1])
+		if nameGaps[i] >= between {
+			t.Errorf("%q stands %.1f px over its box and %q stands %.1f px under that box, so nothing says which box the name belongs to",
+				names[i], nameGaps[i], names[i+1], between)
 		}
 	}
 }

internal/gui/parts/parts.go

@@ -289,7 +289,7 @@ func tipSurface() *canvas.Rectangle {
 // for offsetting shadows. Drawn under tipSurface in a stack, so it shows
 // only past the surface's lower edge.
 func tipShadow() fyne.CanvasObject {
-	rect := canvas.NewRectangle(overlay(0x00, 0x00, 0x00, 0x66))
+	rect := canvas.NewRectangle(PaletteColour(ColorNameTipShade, theme.VariantDark))
 	rect.CornerRadius = RadiusField
 	return container.New(shifted{dy: TipShadowDrop}, rect)
 }

internal/gui/parts/theme.go

@@ -35,6 +35,13 @@ const ColorNamePanel fyne.ThemeColorName = "panel"
 // Owner's decision of 2026-09-21 - see docs/GUI-STRUCTURE-2026-09-21.md.
 const ColorNameLabel fyne.ThemeColorName = "label"
 
+// ColorNameTipShade is the shade an explanation casts on the form under it.
+// A name of its own rather than the toolkit's Shadow, which this palette
+// answers with nothing on purpose (see ColorNameShadow): the toolkit lays its
+// shadow under every popup and the format list is where it read as a hard
+// band, while an explanation is the one floating thing that wanted one.
+const ColorNameTipShade fyne.ThemeColorName = "tipshade"
+
 // ColorNameLift is what the pointer does to a face that is itself light - the
 // filled primary button - and ColorNameShade is what a press does to it.
 //
@@ -193,6 +200,7 @@ var (
 		// than as a popup - see parts.Tips - so it never asked the theme for a
 		// shadow and does not lose one.
 		theme.ColorNameShadow: color.Transparent,
+		ColorNameTipShade:     overlay(0x00, 0x00, 0x00, 0x66),
 
 		// The surface a section is drawn on, and the line round its edge.
 		//
@@ -294,6 +302,7 @@ var (
 		// is what separates it.
 		theme.ColorNameMenuBackground: hex(0xFF, 0xFF, 0xFF),
 		theme.ColorNameShadow:         overlay(0x00, 0x00, 0x00, 0x40),
+		ColorNameTipShade:             overlay(0x00, 0x00, 0x00, 0x40),
 
 		// The same two, worked out the same way against a white page. The gap
 		// between page and input is narrower here - 5.6 L* against 7.7 - so the