fix: cluster base + U+FE0F as a width-2 emoji glyph

src/clayterm.c

@@ -285,6 +285,20 @@ static void render_text(struct Clayterm *ct, int x0, int y0,
       n = 1;
       cp = 0xfffd;
     }
+    /* grapheme cluster: base codepoint + U+FE0F (variation selector-16)
+     * forms a single emoji-presentation glyph of width 2. Place the base
+     * codepoint into the cell (never FE0F) and advance x by 2. */
+    if (rem - n > 0) {
+      uint32_t next;
+      int n2 = utf8_decode(&next, p + n);
+      if (n2 > 0 && n2 <= rem - n && next == 0xfe0f) {
+        setcell(ct, x, y0, cp, fg, ATTR_DEFAULT);
+        x += 2;
+        p += n + n2;
+        rem -= n + n2;
+        continue;
+      }
+    }
     int cw = wcwidth(cp);
     if (cw < 0)
       cw = 1;
@@ -690,6 +704,18 @@ void measure(int ret, int txt) {
     if (n <= 0) {
       n = 1;
     }
+    /* grapheme cluster: base codepoint + U+FE0F (variation selector-16)
+     * forms a single emoji-presentation glyph of width 2 */
+    if (rem - n > 0) {
+      uint32_t next;
+      int n2 = utf8_decode(&next, p + n);
+      if (n2 > 0 && n2 <= rem - n && next == 0xfe0f) {
+        w += 2;
+        p += n + n2;
+        rem -= n + n2;
+        continue;
+      }
+    }
     int cw = wcwidth(cp);
     if (cw > 0)
       w += cw;

test/width.test.ts

@@ -0,0 +1,48 @@
+import { beforeEach, describe, expect, it } from "./suite.ts";
+import { createTerm, type Term } from "../term.ts";
+import { close, fit, open, text } from "../ops.ts";
+import { print } from "./print.ts";
+
+const decode = (b: Uint8Array) => new TextDecoder().decode(b);
+
+const VS16 = "\u{1F321}\u{FE0F}\u{26A0}\u{FE0F}\u{2705}"; // 🌡️⚠️✅
+
+describe("emoji width", () => {
+  let term: Term;
+  beforeEach(async () => {
+    term = await createTerm({ width: 24, height: 3 });
+  });
+
+  it("measures base emoji + U+FE0F as width-2 clusters", () => {
+    let r = term.render([
+      open("box", { layout: { width: fit(), height: fit() } }),
+      text(VS16),
+      close(),
+    ]);
+    // three emoji-presentation clusters at width 2 each => 6, not 4
+    expect(r.info.get("box")!.bounds.width).toBe(6);
+  });
+
+  it("upgrades a single base+FE0F cluster (⚠️) to width 2", () => {
+    let r = term.render([
+      open("box", { layout: { width: fit(), height: fit() } }),
+      text("\u{26A0}\u{FE0F}"), // ⚠️
+      close(),
+    ]);
+    // ⚠ alone is text-presentation width 1; +U+FE0F selects emoji width 2
+    expect(r.info.get("box")!.bounds.width).toBe(2);
+  });
+
+  it("renders each base+FE0F as a width-2 cluster and drops the selector", () => {
+    let r = term.render([
+      open("box", { layout: { width: fit(), height: fit() } }),
+      text(VS16),
+      close(),
+    ]);
+    let grid = print(decode(r.output), 24, 3);
+    // each cluster occupies two columns (base glyph + trailing cell), so the
+    // bases land on even columns; U+FE0F is consumed, never emitted.
+    expect(grid.split("\n")[0].trimEnd()).toBe("🌡 ⚠ ✅");
+    expect(grid).not.toContain("\u{FE0F}");
+  });
+});