Function validateEdits

apps/opencode-plugin/plan-edits.ts:55–91

(existingLines: string[], edits: PlanEdit[])

 * Returns an error string if invalid, or null if all edits are acceptable.
 */
export function validateEdits(existingLines: string[], edits: PlanEdit[]): string | null {
  const lineCount = existingLines.length;

  for (const edit of edits) {
    if (!Number.isInteger(edit.start) || edit.start < 1) {
      return `start must be a positive integer >= 1, got ${edit.start}`;
    }
    if (edit.start > lineCount + 1) {
      return `start (${edit.start}) exceeds file length + 1 (${lineCount + 1})`;
    }
    if (edit.end != null) {
      if (!Number.isInteger(edit.end) || edit.end < edit.start) {
        return `end (${edit.end}) must be >= start (${edit.start})`;
      }
      // On an empty file (lineCount === 0) every edit is a pure insert;
      // end is semantically meaningless and applyEdits handles it via splice
      // clamping. Rejecting here breaks first-call payloads where the agent
      // or framework includes end (see #742).
      if (edit.end > lineCount && lineCount > 0) {
        return `end (${edit.end}) exceeds file length (${lineCount})`;
      }
    }
  }

  const sorted = [...edits].sort((a, b) => a.start - b.start);
  for (let i = 1; i < sorted.length; i++) {
    const prev = sorted[i - 1];
    const curr = sorted[i];
    if (prev.start > lineCount) continue;
    const prevEnd = prev.end ?? lineCount;
    if (curr.start <= prevEnd) {
      return `edits overlap: [${prev.start},${prevEnd}] and [${curr.start},${curr.end ?? "end"}]`;
    }
  }

  return null;
}

/**
 * Format the plan content with line numbers for the agent's reference.