chore: import upstream snapshot with attribution

open-sse/services/compression/engines/rtk/splitCompositeCommand.ts

@@ -0,0 +1,111 @@
+/**
+ * Quote-aware composite-command splitter.
+ *
+ * Splits a shell command string on top-level `&&`, `||`, or `;` separators
+ * (i.e. those NOT inside single quotes, double quotes, backtick subshells,
+ * or `$(...)` subshells) and returns the LAST significant segment (trimmed).
+ *
+ * - No separator found → returns the input unchanged.
+ * - Last segment is empty (e.g. trailing `&&`) → falls back to the previous non-empty one.
+ * - O(n) char-by-char scan; zero RegExp over the full input (anti-ReDoS).
+ */
+export function lastCommandSegment(command: string): string {
+  if (!command) return command;
+
+  const segments: string[] = [];
+  let current = 0; // start index of the current segment
+  let depth = 0; // nesting depth for $(...) / (...)
+  let inSingle = false;
+  let inDouble = false;
+  let inBacktick = false;
+
+  const push = (end: number): void => {
+    segments.push(command.slice(current, end));
+  };
+
+  for (let i = 0; i < command.length; i++) {
+    const ch = command[i];
+
+    // ── quote / subshell state tracking ──────────────────────────────────
+    if (inSingle) {
+      if (ch === "'") inSingle = false;
+      continue;
+    }
+    if (inBacktick) {
+      if (ch === "`") inBacktick = false;
+      continue;
+    }
+    if (inDouble) {
+      if (ch === '"') inDouble = false;
+      // $( inside double-quotes still opens a subshell
+      if (ch === "$" && command[i + 1] === "(") {
+        depth++;
+        i++; // skip the '('
+      }
+      continue;
+    }
+    if (depth > 0) {
+      if (ch === "(") depth++;
+      else if (ch === ")") depth--;
+      continue;
+    }
+
+    // ── open new quote / subshell context ────────────────────────────────
+    if (ch === "'") {
+      inSingle = true;
+      continue;
+    }
+    if (ch === '"') {
+      inDouble = true;
+      continue;
+    }
+    if (ch === "`") {
+      inBacktick = true;
+      continue;
+    }
+    if (ch === "$" && command[i + 1] === "(") {
+      depth++;
+      i++; // skip the '('
+      continue;
+    }
+    if (ch === "(") {
+      depth++;
+      continue;
+    }
+
+    // ── top-level separator detection ─────────────────────────────────────
+    if (ch === "&" && command[i + 1] === "&") {
+      push(i);
+      i += 1; // skip second '&'
+      current = i + 1;
+      continue;
+    }
+    if (ch === "|" && command[i + 1] === "|") {
+      push(i);
+      i += 1; // skip second '|'
+      current = i + 1;
+      continue;
+    }
+    if (ch === ";") {
+      push(i);
+      current = i + 1;
+      continue;
+    }
+  }
+
+  // push the remainder
+  push(command.length);
+
+  if (segments.length === 1) {
+    // no top-level separator found → return unchanged
+    return command;
+  }
+
+  // find the last non-empty (after trim) segment
+  for (let i = segments.length - 1; i >= 0; i--) {
+    const trimmed = segments[i].trim();
+    if (trimmed) return trimmed;
+  }
+
+  return command;
+}