fix(shared): command output no longer prints the final byte of escape sequences with intermediates

packages/shared/src/terminalOutput.test.ts

@@ -128,6 +128,24 @@ describe("appendTerminalOutput under adversarial output", () => {
     }
   });
 
+  it("drops escape sequences with intermediate bytes without printing their final byte", () => {
+    for (const sequence of ["#8", "#6", "%G", " F", "-A", ".A", "(%5", "(B"]) {
+      const input = `a\u001b${sequence}b`;
+      expect(feed([input]).text).toBe("ab");
+      for (let cut = 1; cut < input.length; cut += 1) {
+        expect(feed([input.slice(0, cut), input.slice(cut)]).text).toBe("ab");
+      }
+    }
+    for (const [interrupted, expected] of [
+      ["a\u001b#\u001b[31mb", feed(["a\u001b[31mb"]).text],
+      ["a\u001b#\n8b", "a\n8b"],
+    ] as const) {
+      for (let cut = 0; cut < interrupted.length; cut += 1) {
+        expect(feed([interrupted.slice(0, cut), interrupted.slice(cut)]).text).toBe(expected);
+      }
+    }
+  });
+
   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" +

packages/shared/src/terminalOutput.ts

@@ -265,11 +265,20 @@ function escapeLength(input: string, index: number): number {
     }
     return -1;
   }
-  // Charset designations take three bytes; other sequences take two.
-  if (next === "(" || next === ")" || next === "*" || next === "+") {
-    return index + 2 < input.length ? 3 : -1;
+  // ECMA-35: any intermediate bytes (0x20-0x2F, e.g. charset designations, DECALN) precede one final byte.
+  let cursor = index + 1;
+  while (
+    cursor < input.length &&
+    input.charCodeAt(cursor) >= 0x20 &&
+    input.charCodeAt(cursor) <= 0x2f
+  ) {
+    cursor += 1;
   }
-  return 2;
+  if (cursor >= input.length) return -1;
+  // After intermediates, a control or ESC is not a final byte; end before it so it is still processed.
+  const final = input.charCodeAt(cursor);
+  if (cursor > index + 1 && (final < 0x30 || final > 0x7e)) return cursor - index;
+  return cursor - index + 1;
 }
 
 const penTransitions = new Map<string, string>();