improve(terminal): speed up fitting table rendering (#127221)

* test(terminal): cover fitting table cell rendering

Amp-Thread-ID: https://ampcode.com/threads/T-01a0242a-0302-708f-a777-ec7c0a5c9c60

* perf(terminal): skip wrapping work for fitting ASCII cells

Amp-Thread-ID: https://ampcode.com/threads/T-01a021f5-984a-7628-a30c-491c166ff247

---------

Co-authored-by: Amp <amp@ampcode.com>

packages/terminal-core/src/table.test.ts

@@ -70,6 +70,21 @@ describe("renderTable", () => {
     vi.restoreAllMocks();
   });
 
+  it("renders fitting ASCII cells without grapheme segmentation", () => {
+    const segment = vi.spyOn(Intl.Segmenter.prototype, "segment");
+
+    const out = renderTable({
+      border: "ascii",
+      columns: [{ key: "Name", header: "Name" }],
+      rows: [{ Name: "alpha" }, { Name: "beta" }],
+    });
+
+    expect(out).toBe(
+      ["+-------+", "| Name  |", "+-------+", "| alpha |", "| beta  |", "+-------+", ""].join("\n"),
+    );
+    expect(segment).not.toHaveBeenCalled();
+  });
+
   it.each(["$&", "$`", "$'", "$$"])(
     "displays a literal %s home path in terminal tables",
     (pattern) => {

packages/terminal-core/src/table.ts

@@ -55,8 +55,9 @@ function padCell(text: string, width: number, align: Align): string {
   // A single grapheme wider than the cell (e.g. a width-2 CJK/emoji glyph in a
   // width-1 column) survives wrapLine intact, so clamp here to keep every cell
   // exactly `width` columns and preserve the border-alignment invariant.
-  const content = visibleWidth(text) > width ? truncateToVisibleWidth(text, width) : text;
-  const w = visibleWidth(content);
+  const textWidth = visibleWidth(text);
+  const content = textWidth > width ? truncateToVisibleWidth(text, width) : text;
+  const w = content === text ? textWidth : visibleWidth(content);
   if (w >= width) {
     return content;
   }
@@ -366,6 +367,11 @@ function wrapLine(text: string, width: number): string[] {
   if (width <= 0) {
     return [text];
   }
+  // Fitting edge-trimmed ASCII is one column per code unit and needs no ANSI/grapheme scan.
+  // Keep edge whitespace on the full path, where wrapping preserves its trimming semantics.
+  if (text.length <= width && /^[!-~](?:[ -~]*[!-~])?$/u.test(text)) {
+    return [text];
+  }
 
   // ANSI-aware wrapping: never split inside ANSI SGR/OSC-8 sequences.
   // Table cells are padded and bordered per physical line, so wrapped lines