Pull nearest tilemap uvs a tenth of a texel in, 0.02 still showed lines

At 0.02 texel the lines between tiles of a nearest tilemap were gone at
the zooms tried first, but still showed at others. The user raised the
inset to 0.1 by hand and checked it in the browser.

- A tenth of a texel is still far below half a texel, so the texel
  picked at every pixel centre stays the same.
- The comment names the new value.

Tests:
- tilemap.test.ts follows the value: the inset test expects 0.1/96,
  the sliver test allows up to 0.25 texel from the edge, and the quad
  test checks its uvs to 2 digits instead of 3.
- ./check.sh: 156 files, 2314 tests, CHECK EXIT 0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/viewport/tilemapMesh.ts

@@ -54,8 +54,8 @@ export function tileMesh(
   const half = tile / 2;
   // Linear sampling needs half a texel so the blend never reaches the neighbour. Nearest needs only
   // a sliver: at odd zooms a pixel centre on the quad edge can round onto the neighbour's first
-  // texel and draw a line. 1/50 texel keeps every picked texel the same.
-  const inset = sheet.smooth ? 0.5 : 0.02;
+  // texel and draw a line. 1/10 texel keeps every picked texel the same.
+  const inset = sheet.smooth ? 0.5 : 0.1;
   const insetX = inset / sheet.textureWidth;
   const insetY = inset / sheet.textureHeight;
   let v = 0;

tests/core/tilemap.test.ts

@@ -500,10 +500,10 @@ describe('the mesh a layer becomes', () => {
     expect([positions[0], positions[1]]).toEqual([48, 0]);
     expect([positions[2], positions[3]]).toEqual([72, 0]);
     // Quadrant (0, 0) of a 96 × 144 sheet cut into 24 px quarters is the first quarter of the uvs.
-    expect(uvs[0]).toBeCloseTo(0, 3);
-    expect(uvs[1]).toBeCloseTo(0, 3);
-    expect(uvs[2]).toBeCloseTo(24 / 96, 3);
-    expect(uvs[3]).toBeCloseTo(0, 3);
+    expect(uvs[0]).toBeCloseTo(0, 2);
+    expect(uvs[1]).toBeCloseTo(0, 2);
+    expect(uvs[2]).toBeCloseTo(24 / 96, 2);
+    expect(uvs[3]).toBeCloseTo(0, 2);
   });
 
   it('pulls the uvs half a texel in when the picture is sampled smoothly', () => {
@@ -527,7 +527,7 @@ describe('the mesh a layer becomes', () => {
     ];
     const hard = tileMesh(tiles, 48, { x: 0, y: 0 }, { ...sheet, smooth: false });
     const soft = tileMesh(tiles, 48, { x: 0, y: 0 }, { ...sheet, smooth: true });
-    expect(hard.uvs[0]).toBeCloseTo(0.02 / 96, 6);
+    expect(hard.uvs[0]).toBeCloseTo(0.1 / 96, 6);
     expect(soft.uvs[0]).toBeCloseTo(0.5 / 96, 6);
     // The positions are untouched: only what is sampled moves, never where it lands.
     expect([...soft.positions]).toEqual([...hard.positions]);
@@ -560,7 +560,7 @@ describe('the mesh a layer becomes', () => {
     for (const t of [...us, ...vs]) {
       expect(t).toBeGreaterThan(24);
       expect(t).toBeLessThan(48);
-      expect(Math.min(t - 24, 48 - t)).toBeLessThan(0.05);
+      expect(Math.min(t - 24, 48 - t)).toBeLessThan(0.25);
     }
   });
 });