Give the app a mark that survives being 16 pixels tall

The icon is now a container with its right wall opened, so the enclosure
itself is the letter C, holding a >_ prompt: the two things the app is,
in one closed shape. It carries no type, so nothing goes illegible when
the shell draws it small, and it uses the app's own accent tokens rather
than a saturated orange field that fights the chrome behind it.

icon.ico contained a single 16x16 image, which Windows was upscaling into
the taskbar and every other slot — the likely cause of the artefact in
screenshot_for_fix/. It now carries 16, 24, 32, 48, 64, 128 and 256, each
rendered from vector rather than downsampled from one bitmap, and the
entries at 32 and below come from a separate optical source: at that size
the cursor bar closes up against the chevron, so the small variant drops
it, widens the mouth and thickens the strokes. A test asserts the .ico
keeps its small sizes so this cannot regress silently.

Also adds the icon.icns that macOS bundles have been building without,
points the favicon at our own mark instead of the missing /vite.svg, and
puts the SVG sources, the lockups and the regeneration script in
branding/.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

branding/README.md

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+# Branding
+
+The mark is a container with its right wall opened, so the enclosure itself is the letter **C**,
+holding a `>_` prompt. Container plus shell, in one closed shape — no type inside the icon, so
+nothing goes illegible when the app is 16 px tall in a taskbar.
+
+## Files
+
+| File | What it is |
+|---|---|
+| `triple-c-mark.svg` | The mark alone, transparent. Use on any ground. |
+| `triple-c-mark-small.svg` | Optical variant for 32 px and below. |
+| `triple-c-icon.svg` | The app icon: mark at 70% on a `#0D1117` tile, 22% corner radius. |
+| `triple-c-icon-small.svg` | The app icon at small sizes — small mark, drawn at 82%. |
+| `triple-c-lockup-dark.svg` | Horizontal lockup for dark backgrounds. Wordmark is outlined, so no font is needed to render it. |
+| `triple-c-lockup-light.svg` | The same for light backgrounds. |
+| `triple-c-icon-1024.png` | Master raster, generated. |
+| `build-icons.py` | Regenerates every packaged icon from the SVGs. |
+
+## Palette
+
+| Role | Dark ground | Light ground |
+|---|---|---|
+| Frame | `#58A6FF` (`--accent`) | `#1F6FEB` (`--accent-emphasis`) |
+| Prompt | `#F0821E` | `#C4610F` |
+| Tile | `#0D1117` (`--bg-primary`) | — |
+| Wordmark | `#E6EDF3` (`--text-primary`) | `#131C25` |
+
+The frame and prompt colours are the app's own accent tokens from `app/src/index.css`, which is why
+the icon sits on the app's chrome instead of fighting it. Orange is the only equity carried over
+from the previous marks, and it is now an accent rather than a background.
+
+## Two sources, not one
+
+`build-icons.py` renders sizes ≥ 48 px from `triple-c-icon.svg` and sizes ≤ 32 px from
+`triple-c-icon-small.svg`. At small sizes the cursor bar closes up against the chevron and a 12 px
+frame stroke resamples to a grey smear, so the small variant drops the cursor, widens the mouth,
+thickens the strokes and draws the mark larger inside the tile.
+
+This matters most for `icon.ico`: Windows picks the 16 px entry for the window corner and 24/32 px
+for the taskbar. The previous `.ico` contained a *single* 16 px image, which Windows then upscaled
+everywhere else — the likely cause of `screenshot_for_fix/task_bar_icon_not_correct.png`. The
+current one carries 16, 24, 32, 48, 64, 128 and 256, each rendered from vector rather than
+downsampled from one bitmap.
+
+## Regenerating
+
+```bash
+pip install cairosvg pillow
+python3 branding/build-icons.py
+```
+
+Writes `app/src-tauri/icons/{32x32,128x128,128x128@2x,icon}.png`, `icon.ico`, `icon.icns`,
+`app/public/favicon.svg` and `branding/triple-c-icon-1024.png`. Do not hand-edit those — edit the
+SVG and re-run.
+
+The lockups are committed sources, not generated: their wordmark is Liberation Mono Bold converted
+to outlines (`-1.6` tracking, 44 px cap height), so re-cutting it needs the font and `fonttools`.

branding/build-icons.py

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+#!/usr/bin/env python3
+"""Render every packaged icon from the SVG sources in this directory.
+
+    pip install cairosvg pillow
+    python3 branding/build-icons.py
+
+The SVGs are the source of truth; everything under app/src-tauri/icons/ and the
+favicon are generated. Two sources, not one, on purpose:
+
+    triple-c-icon.svg        used for 48 px and up
+    triple-c-icon-small.svg  used for 32 px and down
+
+At 16-32 px the cursor bar closes up against the chevron and the frame's 12 px
+stroke resamples to a grey smear, so the small source drops the cursor, widens
+the mouth and draws the mark larger in the tile. Windows picks the 16 and 24 px
+entries out of the .ico for the taskbar and window corner, which is exactly
+where the old single-size .ico was falling over.
+"""
+
+import io
+import struct
+from pathlib import Path
+
+import cairosvg
+from PIL import Image
+
+BRANDING = Path(__file__).resolve().parent
+REPO = BRANDING.parent
+ICONS = REPO / "app" / "src-tauri" / "icons"
+PUBLIC = REPO / "app" / "public"
+
+FULL_SRC = BRANDING / "triple-c-icon.svg"
+SMALL_SRC = BRANDING / "triple-c-icon-small.svg"
+
+# Below this, render from the small source.
+SMALL_MAX = 32
+
+# .ico entries. Windows uses 16 in the window corner and 24/32 in the taskbar,
+# 48 in list views and 256 in the "extra large icons" view.
+ICO_SIZES = [16, 24, 32, 48, 64, 128, 256]
+
+# .icns entries: (chunk type, pixel size). PNG-backed chunks, macOS 10.7+.
+ICNS_ENTRIES = [
+    (b"ic11", 32),    # 16pt @2x
+    (b"ic12", 64),    # 32pt @2x
+    (b"ic07", 128),   # 128pt
+    (b"ic13", 256),   # 128pt @2x
+    (b"ic08", 256),   # 256pt
+    (b"ic14", 512),   # 256pt @2x
+    (b"ic09", 512),   # 512pt
+    (b"ic10", 1024),  # 512pt @2x
+]
+
+
+def render(size: int) -> Image.Image:
+    """Rasterise the right source at `size` px square."""
+    src = SMALL_SRC if size <= SMALL_MAX else FULL_SRC
+    png = cairosvg.svg2png(url=str(src), output_width=size, output_height=size)
+    return Image.open(io.BytesIO(png)).convert("RGBA")
+
+
+def write_png(size: int, path: Path) -> None:
+    render(size).save(path, "PNG", optimize=True)
+    print(f"  {path.relative_to(REPO)}  {size}x{size}")
+
+
+def write_ico(path: Path) -> None:
+    """Hand-assemble the .ico so each entry can come from its own source.
+
+    Pillow's save(sizes=...) downsamples one image, which would put the
+    12 px-stroke artwork into the 16 px entry — the thing this avoids.
+    """
+    images = [render(s) for s in ICO_SIZES]
+    payloads = []
+    for img in images:
+        buf = io.BytesIO()
+        img.save(buf, "PNG", optimize=True)  # PNG-compressed entries, Vista+
+        payloads.append(buf.getvalue())
+
+    offset = 6 + 16 * len(images)
+    header = struct.pack("<HHH", 0, 1, len(images))
+    entries, blob = b"", b""
+    for img, data in zip(images, payloads):
+        w = 0 if img.width >= 256 else img.width
+        h = 0 if img.height >= 256 else img.height
+        entries += struct.pack("<BBBBHHII", w, h, 0, 0, 1, 32, len(data), offset)
+        blob += data
+        offset += len(data)
+    path.write_bytes(header + entries + blob)
+    print(f"  {path.relative_to(REPO)}  {', '.join(str(s) for s in ICO_SIZES)}")
+
+
+def write_icns(path: Path) -> None:
+    chunks = b""
+    for kind, size in ICNS_ENTRIES:
+        buf = io.BytesIO()
+        render(size).save(buf, "PNG", optimize=True)
+        data = buf.getvalue()
+        chunks += kind + struct.pack(">I", len(data) + 8) + data
+    path.write_bytes(b"icns" + struct.pack(">I", len(chunks) + 8) + chunks)
+    print(f"  {path.relative_to(REPO)}  {', '.join(str(s) for _, s in ICNS_ENTRIES)}")
+
+
+def main() -> None:
+    print("branding/")
+    write_png(1024, BRANDING / "triple-c-icon-1024.png")
+
+    print("app/src-tauri/icons/")
+    write_png(32, ICONS / "32x32.png")
+    write_png(128, ICONS / "128x128.png")
+    write_png(256, ICONS / "128x128@2x.png")
+    write_png(512, ICONS / "icon.png")
+    write_ico(ICONS / "icon.ico")
+    write_icns(ICONS / "icon.icns")
+
+    print("app/public/")
+    (PUBLIC / "favicon.svg").write_text(SMALL_SRC.read_text())
+    print(f"  {(PUBLIC / 'favicon.svg').relative_to(REPO)}  (copy of {SMALL_SRC.name})")
+
+
+if __name__ == "__main__":
+    main()

branding/triple-c-icon-small.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 128 128" width="128" height="128" role="img" aria-label="Triple-C">
+  <title>Triple-C application icon, small-size variant</title>
+  <!-- Source for every raster ≤ 32 px: the small mark, drawn at 82% so the strokes
+       survive being resampled down to 16 px. See build-icons.py. -->
+  <rect width="128" height="128" rx="28.16" fill="#0D1117"/>
+  <g transform="translate(2.9236 2.9236) scale(0.95418)">
+    <g fill="none" stroke-linecap="round" stroke-linejoin="round">
+      <path d="M112 50 L112 38 A22 22 0 0 0 90 16 L38 16 A22 22 0 0 0 16 38 L16 90 A22 22 0 0 0 38 112 L90 112 A22 22 0 0 0 112 90 L112 78"
+            stroke="#58A6FF" stroke-width="14"/>
+      <path d="M46 50 L62 66 L46 82" stroke="#F0821E" stroke-width="13"/>
+    </g>
+  </g>
+</svg>

branding/triple-c-icon.svg

@@ -0,0 +1,14 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 128 128" width="128" height="128" role="img" aria-label="Triple-C">
+  <title>Triple-C application icon</title>
+  <!-- App icon: the mark on the app's own ground (bg-primary), at 70% of the tile.
+       Source for every raster ≥ 48 px. See build-icons.py. -->
+  <rect width="128" height="128" rx="28.16" fill="#0D1117"/>
+  <g transform="translate(10.8988 10.8988) scale(0.82963)">
+    <g fill="none" stroke-linecap="round" stroke-linejoin="round">
+      <path d="M112 46 L112 38 A22 22 0 0 0 90 16 L38 16 A22 22 0 0 0 16 38 L16 90 A22 22 0 0 0 38 112 L90 112 A22 22 0 0 0 112 90 L112 82"
+            stroke="#58A6FF" stroke-width="12"/>
+      <path d="M42 50 L58 66 L42 82" stroke="#F0821E" stroke-width="11"/>
+      <path d="M68 82 L88 82" stroke="#F0821E" stroke-width="11"/>
+    </g>
+  </g>
+</svg>

branding/triple-c-mark-small.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 128 128" width="128" height="128" role="img" aria-label="Triple-C">
+  <title>Triple-C mark, small-size variant</title>
+  <!-- Optical variant for 32 px and below: heavier strokes, wider mouth, no cursor bar.
+       Below ~40 px the cursor closes up against the chevron and the frame goes to mush. -->
+  <g fill="none" stroke-linecap="round" stroke-linejoin="round">
+    <path d="M112 50 L112 38 A22 22 0 0 0 90 16 L38 16 A22 22 0 0 0 16 38 L16 90 A22 22 0 0 0 38 112 L90 112 A22 22 0 0 0 112 90 L112 78"
+          stroke="#58A6FF" stroke-width="14"/>
+    <path d="M46 50 L62 66 L46 82" stroke="#F0821E" stroke-width="13"/>
+  </g>
+</svg>

branding/triple-c-mark.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 128 128" width="128" height="128" role="img" aria-label="Triple-C">
+  <title>Triple-C mark</title>
+  <!-- The container frame, opened on the right so the enclosure itself is the letter C. -->
+  <g fill="none" stroke-linecap="round" stroke-linejoin="round">
+    <path d="M112 46 L112 38 A22 22 0 0 0 90 16 L38 16 A22 22 0 0 0 16 38 L16 90 A22 22 0 0 0 38 112 L90 112 A22 22 0 0 0 112 90 L112 82"
+          stroke="#58A6FF" stroke-width="12"/>
+    <!-- The prompt: chevron and cursor. -->
+    <path d="M42 50 L58 66 L42 82" stroke="#F0821E" stroke-width="11"/>
+    <path d="M68 82 L88 82" stroke="#F0821E" stroke-width="11"/>
+  </g>
+</svg>