fix(frontend): raise dark contrast, expand hit areas, and surface input limits

Dark muted surfaces missed WCAG AA; action and tertiary tokens plus a 32-pair contract close that. Hit targets, remaining-count, and Enter-to-send follow the interaction audit without changing visual sizes.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/tests/dark-theme-contract.test.ts

@@ -64,15 +64,43 @@ test("dark ink reads lighter than dark canvas, and the action stays legible", ()
     const [hi, lo] = [luminance(a), luminance(b)].sort((x, y) => y - x);
     return (hi + 0.05) / (lo + 0.05);
   };
-  const canvas = pinned.get("color-canvas")!;
-  for (const token of ["color-ink", "color-action", "color-danger", "color-success", "color-warning"]) {
-    const value = pinned.get(token)!;
-    assert.match(value, /^#[0-9a-f]{6}$/i, `--${token} must be a hex so contrast is checkable`);
-    assert.ok(
-      contrast(value, canvas) >= 4.5,
-      `--${token} (${value}) on --color-canvas (${canvas}) is ${contrast(value, canvas).toFixed(2)}:1, below AA`,
-    );
+  // Checking only the reading surface missed ink-tertiary and action on the
+  // raised card (--color-canvas-muted). New text or surface tokens must join
+  // this matrix; do not drop a pair or lower 4.5 to make it pass.
+  const inks = [
+    "color-ink",
+    "color-ink-strong",
+    "color-ink-secondary",
+    "color-ink-tertiary",
+    "color-action",
+    "color-danger",
+    "color-success",
+    "color-warning",
+  ];
+  const surfaces = [
+    "color-canvas",
+    "color-canvas-soft",
+    "color-canvas-muted",
+    "color-sidebar-solid",
+  ];
+  const failures: string[] = [];
+  for (const ink of inks) {
+    const inkValue = pinned.get(ink)!;
+    assert.match(inkValue, /^#[0-9a-f]{6}$/i, `--${ink} must be a hex so contrast is checkable`);
+    for (const surface of surfaces) {
+      const surfaceValue = pinned.get(surface)!;
+      assert.match(
+        surfaceValue,
+        /^#[0-9a-f]{6}$/i,
+        `--${surface} must be a hex so contrast is checkable`,
+      );
+      const ratio = contrast(inkValue, surfaceValue);
+      if (ratio < 4.5) {
+        failures.push(`--${ink} (${inkValue}) on --${surface} (${surfaceValue}) is ${ratio.toFixed(2)}:1`);
+      }
+    }
   }
+  assert.equal(failures.length, 0, failures.join("; "));
   // Elevation reads through lightness on dark: floor is darkest, raised steps up.
   const steps = ["color-canvas-soft", "color-canvas", "color-canvas-muted", "color-canvas-strong"]
     .map((token) => luminance(pinned.get(token)!));
@@ -80,3 +108,22 @@ test("dark ink reads lighter than dark canvas, and the action stays legible", ()
     assert.ok(steps[i] > steps[i - 1], "dark surfaces must get lighter as they rise");
   }
 });
+
+test("the previous dark action and tertiary hexes are gone from product sources", () => {
+  const sources = [
+    globalStyles,
+    readFileSync(new URL("../src/app/error.tsx", import.meta.url), "utf8"),
+    readFileSync(new URL("../src/app/not-found.tsx", import.meta.url), "utf8"),
+    readFileSync(new URL("../src/app/forbidden.tsx", import.meta.url), "utf8"),
+    readFileSync(new URL("../src/app/global-error.tsx", import.meta.url), "utf8"),
+    readFileSync(new URL("../DESIGN.md", import.meta.url), "utf8"),
+  ];
+  for (const source of sources) {
+    assert.doesNotMatch(source, /#d4785a/i);
+  }
+  assert.equal(pinned.get("color-action"), "#d78064");
+  assert.equal(pinned.get("color-focus"), "#d78064");
+  assert.equal(pinned.get("color-ink-tertiary"), "#9c988e");
+  assert.equal(preferred.get("color-action"), "#d78064");
+  assert.equal(preferred.get("color-ink-tertiary"), "#9c988e");
+});