perf(shared): skip parsing cached terminal styles

packages/shared/src/terminalOutput.test.ts

@@ -103,10 +103,15 @@ describe("appendTerminalOutput edge cases from review", () => {
 
 describe("appendTerminalOutput under adversarial output", () => {
   it("gives the same result however the output is split into chunks", () => {
-    const input = "abcdef\rX\u001b[31mred\u001b[0m\nnext line\r\u001b[2Kdone\n";
-    const whole = feed([input], 3).text;
-    for (let cut = 1; cut < input.length; cut += 1) {
-      expect(feed([input.slice(0, cut), input.slice(cut)], 3).text).toBe(whole);
+    const input =
+      "abcdef\rX\u001b[31mred\u001b[0m\nnext line\r\u001b[2Kdone\n" +
+      "\u001b[1;31mbold red\u001b[mplain\u001b[38:2::12:34:56mrgb\u001b[0m\n" +
+      "\u001b[1;31mbold red again\u001b[mplain again\u001b[38:2::12:34:56mrgb again\u001b[0m";
+    for (const maxChars of [3, 1_024]) {
+      const whole = feed([input], maxChars).text;
+      for (let cut = 1; cut < input.length; cut += 1) {
+        expect(feed([input.slice(0, cut), input.slice(cut)], maxChars).text).toBe(whole);
+      }
     }
     expect(feed(["abcdef", "\rX"], 3).text).toBe(feed(["abcdef\rX"], 3).text);
   });

packages/shared/src/terminalOutput.ts

@@ -389,22 +389,22 @@ class Terminal {
 
   csi(params: string, final: string): void {
     if (/^[?>=]/u.test(params)) return; // Mode switches (cursor visibility, bracketed paste).
+    if (final === "m") {
+      const key = `${this.pen}|${params}`;
+      let pen = penTransitions.get(key);
+      if (pen === undefined) {
+        const attributes = parsePen(this.pen);
+        applySgr(attributes, params === "" ? [] : csiParams(params));
+        pen = formatPen(attributes);
+        if (penTransitions.size >= 512) penTransitions.clear();
+        penTransitions.set(key, pen);
+      }
+      this.pen = pen;
+      return;
+    }
     const numbers = params === "" ? [] : csiParams(params);
     const count = Math.max(1, numbers[0] || 1);
     switch (final) {
-      case "m": {
-        const key = `${this.pen}|${params}`;
-        let pen = penTransitions.get(key);
-        if (pen === undefined) {
-          const attributes = parsePen(this.pen);
-          applySgr(attributes, numbers);
-          pen = formatPen(attributes);
-          if (penTransitions.size >= 512) penTransitions.clear();
-          penTransitions.set(key, pen);
-        }
-        this.pen = pen;
-        return;
-      }
       case "A":
         return this.moveTo(this.row - count, this.col);
       case "B":