style(header): hover moves the icon, never the button

A global `.btn-icon-header:hover { transform: rotate(45deg) }`, meant for
the settings gear, turned every header icon button on hover, so the folder,
Tiles, Split and the rest swung their rounded hover background into a
diamond. Three buttons had already cancelled it one by one (the font-size
buttons, notifications, the sidebar toggle).

The rule is gone, and with it those three overrides. Hover motion now moves
the icon only:
- the settings gear's icon turns 45 degrees (one tooth, so it lands on the
  same shape);
- the Tiles button's four squares spread apart, each toward its corner;
- the folder cross-fades to an open folder (a second drawing in its SVG,
  `.icon-folder-closed` / `.icon-folder-open`);
- every other icon just takes the hover colour.

Pointer devices only (`@media (hover: hover)`, so a tap cannot leave an icon
stuck mid-motion), and the transitions are off under reduced motion.

Owner request: the Tiles and folder buttons "weirdly turn" on hover.
Checked live on a dark and a light skin (rest, mid, end frames). Pinned by
test/header-icon-hover.test.ts, mutation-checked five ways (the button
rotation back, the open drawing missing, the motion not hover-gated, a
square spreading toward the wrong corner, reduced motion keeping its
transition). Gate: 507 files, 9798 tests passed.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/tile-grid-plan.md

@@ -68,6 +68,15 @@ or settled a question the spec left open. The invariants as built are in
   every joining tile mounted and laid out before any connects (one fit, one PTY resize
   each), and a zoom the user chose ends. The other ways in (Ctrl/Cmd+click, a dragged tab,
   "Open group as tiles", Run) still add up to the cap of 6.
+- **Header icons move their icon on hover, never the button** (owner request: the Tiles
+  and folder buttons "weirdly turn" on hover; make a nicer hover). A global
+  `.btn-icon-header:hover { transform: rotate(45deg) }` (meant for the settings gear)
+  turned every header icon button, swinging its hover background into a diamond. Now
+  only the gear's ICON turns (45 degrees, one tooth), the Tiles button's four squares
+  spread apart, and the folder cross-fades to an open folder (`.icon-folder-closed` /
+  `.icon-folder-open` in its SVG); every other icon just takes the hover colour. Pointer
+  devices only (`@media (hover: hover)`), transitions off under reduced motion. Pinned by
+  `test/header-icon-hover.test.ts`.
 - **The grid opens and closes with a short animation, on by default** (owner request:
   "when clicking on the tile button first make this animation nicer"). It is the grid's
   own, not an `entrance-animations.js` theme (those are off by default). Opening, each tile

src/web/public/index.html

@@ -189,7 +189,7 @@
           <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="m21.44 11.05-9.19 9.19a6 6 0 0 1-8.49-8.49l9.19-9.19a4 4 0 0 1 5.66 5.66l-9.2 9.19a2 2 0 0 1-2.83-2.83l8.49-8.48"/></svg>
           <span class="attachment-history-badge" id="attachmentHistoryBadge" style="display:none;">0</span>
         </button>
-        <button class="btn-icon-header btn-file-viewer" onclick="app.toggleFileBrowserButton()" title="File Viewer" aria-label="Open file viewer" aria-expanded="false"><svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M3 7a2 2 0 0 1 2-2h4l2 2h8a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2z"/></svg></button>
+        <button class="btn-icon-header btn-file-viewer" onclick="app.toggleFileBrowserButton()" title="File Viewer" aria-label="Open file viewer" aria-expanded="false"><svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path class="icon-folder-closed" d="M3 7a2 2 0 0 1 2-2h4l2 2h8a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2z"/><g class="icon-folder-open"><path d="M3 17V7a2 2 0 0 1 2-2h4l2 2h6a2 2 0 0 1 2 2v1.5"/><path d="M3 17l2.3-5.4A2 2 0 0 1 7.2 10.5H20a1.5 1.5 0 0 1 1.4 2l-1.9 5.2A2 2 0 0 1 17.6 19H5a2 2 0 0 1-2-2z"/></g></svg></button>
         <button class="btn-icon-header btn-multimonitor btn-multimonitor--hidden" onclick="app.launchMultiMonitor()" title="Open Codeman across all displays" aria-label="Open Codeman across all displays"><svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><rect x="2" y="4" width="13" height="9" rx="1.5"/><rect x="11" y="9" width="11" height="8" rx="1.5"/></svg></button>
         <button class="btn-icon-header btn-split btn-split--hidden" onclick="app.openSplitPicker(event)" title="Split: open a second session beside this one" aria-label="Split: open a second session beside this one" aria-pressed="false"><svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><rect x="2" y="3" width="20" height="18" rx="2"/><line x1="12" y1="3" x2="12" y2="21"/></svg></button>
         <button class="btn-icon-header btn-tile-grid btn-tile-grid--hidden" onclick="app.toggleTileGrid()" oncontextmenu="app.openTileCountMenu(event)" title="Tiles: show several sessions side by side (right-click for how many)" aria-label="Tiles: show several sessions side by side (right-click for how many)" aria-pressed="false"><svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><rect x="3" y="3" width="8" height="8" rx="1"/><rect x="13" y="3" width="8" height="8" rx="1"/><rect x="3" y="13" width="8" height="8" rx="1"/><rect x="13" y="13" width="8" height="8" rx="1"/></svg></button>

src/web/public/styles.css

@@ -2450,9 +2450,75 @@ html[data-tab-orientation='vertical'].tab-rail-compact
 .btn-icon-header:hover {
   background: rgba(255, 255, 255, 0.07);
   color: var(--text);
+}
+
+/* Hover motion moves the icon, never the button: turning the whole button used
+   to swing its hover background into a diamond on every header icon. Now only the
+   gear turns, the folder opens and the Tiles squares spread apart; every other
+   icon just takes the hover colour. Pointer devices only (a tap must not leave an
+   icon stuck mid-motion), and no motion at all under reduced motion. */
+.btn-icon-header.btn-settings svg,
+.btn-icon-header.btn-tile-grid svg rect,
+.btn-icon-header.btn-file-viewer svg .icon-folder-closed,
+.btn-icon-header.btn-file-viewer svg .icon-folder-open {
+  transition: transform 260ms cubic-bezier(0.34, 1.56, 0.64, 1), opacity 160ms ease;
+}
+
+.btn-icon-header.btn-tile-grid svg rect {
+  transform-box: fill-box;
+  transform-origin: center;
+}
+
+.btn-icon-header.btn-file-viewer svg .icon-folder-open {
+  opacity: 0;
+  transform: translateY(1px);
+}
+
+@media (hover: hover) {
+  .btn-icon-header.btn-settings:hover svg {
     transform: rotate(45deg);
   }
 
+  .btn-icon-header.btn-tile-grid:hover svg rect:nth-of-type(1) {
+    transform: translate(-1.5px, -1.5px);
+  }
+
+  .btn-icon-header.btn-tile-grid:hover svg rect:nth-of-type(2) {
+    transform: translate(1.5px, -1.5px);
+  }
+
+  .btn-icon-header.btn-tile-grid:hover svg rect:nth-of-type(3) {
+    transform: translate(-1.5px, 1.5px);
+  }
+
+  .btn-icon-header.btn-tile-grid:hover svg rect:nth-of-type(4) {
+    transform: translate(1.5px, 1.5px);
+  }
+
+  .btn-icon-header.btn-file-viewer:hover svg .icon-folder-closed {
+    opacity: 0;
+  }
+
+  .btn-icon-header.btn-file-viewer:hover svg .icon-folder-open {
+    opacity: 1;
+    transform: none;
+  }
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .btn-icon-header.btn-settings svg,
+  .btn-icon-header.btn-tile-grid svg rect,
+  .btn-icon-header.btn-file-viewer svg .icon-folder-closed,
+  .btn-icon-header.btn-file-viewer svg .icon-folder-open {
+    transition: none;
+  }
+
+  .btn-icon-header.btn-settings:hover svg,
+  .btn-icon-header.btn-tile-grid:hover svg rect {
+    transform: none;
+  }
+}
+
 /* Admin Panel header button: only shown to admins in multi-user mode (marker
    class removed by admin-ui.js after identity boot). Deliberately BIG and
    prominent: it is the entry point to user/permission management. */
@@ -2569,10 +2635,6 @@ html[data-tab-orientation='vertical'].tab-rail-compact
   font-weight: 600;
 }
 
-.btn-icon-header.btn-sm:hover {
-  transform: none;
-}
-
 .header-font-controls {
   display: flex;
   align-items: center;
@@ -9195,10 +9257,6 @@ kbd {
   margin-right: 2px;
 }
 
-.btn-icon-header.btn-notifications:hover {
-  transform: none;
-}
-
 .notification-badge {
   position: absolute;
   top: 2px;
@@ -19172,11 +19230,6 @@ html[data-session-list="sidebar"][data-sidebar="collapsed"] .session-sidebar .ta
   display: none !important;
 }
 
-/* .btn-icon-header:hover rotates 45deg globally — a panel glyph must not spin. */
-.btn-sidebar-toggle:hover {
-  transform: none;
-}
-
 html[data-session-list="sidebar"][data-sidebar="collapsed"] .btn-sidebar-toggle svg {
   transform: scaleX(-1);
 }

test/header-icon-hover.test.ts

@@ -0,0 +1,125 @@
+/**
+ * @fileoverview Header icon buttons: hover motion moves the icon, never the button.
+ *
+ * A global `.btn-icon-header:hover { transform: rotate(45deg) }` (meant for the
+ * settings gear) turned EVERY header icon button on hover, so the folder, Tiles,
+ * Split and the rest swung their rounded hover background into a diamond. Three
+ * buttons had already been patched one by one with `transform: none`. The owner
+ * asked for a nicer hover on the folder and Tiles buttons; this file pins the
+ * shape of the fix:
+ *
+ * 1. No rule on a header icon button transforms the BUTTON on hover.
+ * 2. Only the gear's icon turns; the Tiles squares spread apart; the folder
+ *    cross-fades from closed to open (two drawings in its SVG).
+ * 3. Those motions live inside `@media (hover: hover)`, so a tap on a touch
+ *    screen cannot leave an icon stuck mid-motion, and reduced motion turns the
+ *    transitions off.
+ */
+import { describe, expect, it } from 'vitest';
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+import postcss, { type AtRule, type Rule } from 'postcss';
+
+const ROOT = resolve(__dirname, '..');
+const css = readFileSync(resolve(ROOT, 'src/web/public/styles.css'), 'utf8');
+const html = readFileSync(resolve(ROOT, 'src/web/public/index.html'), 'utf8');
+const root = postcss.parse(css);
+
+interface FoundRule {
+  selector: string;
+  decls: Record<string, string>;
+  media: string[];
+}
+
+function rules(): FoundRule[] {
+  const out: FoundRule[] = [];
+  root.walkRules((rule: Rule) => {
+    const media: string[] = [];
+    for (let p = rule.parent; p && p.type !== 'root'; p = p.parent) {
+      if (p.type === 'atrule' && (p as AtRule).name === 'media') media.push((p as AtRule).params);
+    }
+    const decls: Record<string, string> = {};
+    rule.walkDecls((d) => {
+      decls[d.prop] = d.value;
+    });
+    for (const selector of rule.selectors) out.push({ selector, decls, media });
+  });
+  return out;
+}
+
+const all = rules();
+const iconRules = all.filter((r) => r.selector.includes('btn-icon-header'));
+
+function buttonTag(cls: string): string {
+  const i = html.indexOf(`class="btn-icon-header ${cls}`);
+  expect(i, `${cls} button in index.html`).toBeGreaterThan(-1);
+  return html.slice(i, html.indexOf('</button>', i));
+}
+
+describe('header icon hover', () => {
+  it('never transforms the button itself on hover', () => {
+    const offenders = iconRules.filter(
+      (r) => /:hover\s*$/.test(r.selector) && r.decls.transform && r.decls.transform !== 'none'
+    );
+    expect(offenders.map((r) => `${r.selector} { transform: ${r.decls.transform} }`)).toEqual([]);
+  });
+
+  it('turns only the gear icon, and only on pointer devices', () => {
+    const rotations = iconRules.filter((r) => /rotate\(/.test(r.decls.transform || ''));
+    expect(rotations.map((r) => r.selector)).toEqual(['.btn-icon-header.btn-settings:hover svg']);
+    expect(rotations[0].media).toContain('(hover: hover)');
+  });
+
+  it('spreads the four Tiles squares apart, each toward its own corner', () => {
+    const svg = buttonTag('btn-tile-grid');
+    expect(svg.match(/<rect /g)?.length).toBe(4);
+    const expected = ['(-1.5px, -1.5px)', '(1.5px, -1.5px)', '(-1.5px, 1.5px)', '(1.5px, 1.5px)'];
+    expected.forEach((offset, i) => {
+      const rule = iconRules.find(
+        (r) => r.selector === `.btn-icon-header.btn-tile-grid:hover svg rect:nth-of-type(${i + 1})`
+      );
+      expect(rule?.decls.transform, `rect ${i + 1}`).toBe(`translate${offset}`);
+      expect(rule?.media).toContain('(hover: hover)');
+    });
+    const box = iconRules.find(
+      (r) => r.selector === '.btn-icon-header.btn-tile-grid svg rect' && r.decls['transform-box']
+    );
+    expect(box?.decls['transform-origin']).toBe('center');
+  });
+
+  it('opens the folder: the open drawing is hidden at rest and replaces the closed one on hover', () => {
+    const svg = buttonTag('btn-file-viewer');
+    expect(svg).toContain('class="icon-folder-closed"');
+    expect(svg).toContain('class="icon-folder-open"');
+    const rest = iconRules.find(
+      (r) => r.selector === '.btn-icon-header.btn-file-viewer svg .icon-folder-open' && r.decls.opacity
+    );
+    expect(rest?.decls.opacity).toBe('0');
+    expect(rest?.media).toEqual([]);
+    const hoverClosed = iconRules.find(
+      (r) => r.selector === '.btn-icon-header.btn-file-viewer:hover svg .icon-folder-closed'
+    );
+    const hoverOpen = iconRules.find(
+      (r) => r.selector === '.btn-icon-header.btn-file-viewer:hover svg .icon-folder-open'
+    );
+    expect(hoverClosed?.decls.opacity).toBe('0');
+    expect(hoverOpen?.decls.opacity).toBe('1');
+    expect(hoverClosed?.media).toContain('(hover: hover)');
+    expect(hoverOpen?.media).toContain('(hover: hover)');
+  });
+
+  it('turns the motion off under reduced motion', () => {
+    const reduced = iconRules.filter((r) => r.media.includes('(prefers-reduced-motion: reduce)'));
+    for (const sel of [
+      '.btn-icon-header.btn-settings svg',
+      '.btn-icon-header.btn-tile-grid svg rect',
+      '.btn-icon-header.btn-file-viewer svg .icon-folder-closed',
+      '.btn-icon-header.btn-file-viewer svg .icon-folder-open',
+    ]) {
+      expect(reduced.find((r) => r.selector === sel)?.decls.transition, sel).toBe('none');
+    }
+    for (const sel of ['.btn-icon-header.btn-settings:hover svg', '.btn-icon-header.btn-tile-grid:hover svg rect']) {
+      expect(reduced.find((r) => r.selector === sel)?.decls.transform, sel).toBe('none');
+    }
+  });
+});