feat(billing): bill Cursor executor usage via stream-json token parsing

Parse Cursor CLI usage from stream-json output and charge through billSessionUsage so subscription quota is consumed first and wallet overage applies when needed.

Co-authored-by: Cursor <cursoragent@cursor.com>

cursor-agent-usage.mjs

@@ -0,0 +1,90 @@
+function parseStreamJsonLine(line) {
+  const text = String(line ?? '').trim();
+  if (!text) return null;
+  try {
+    const parsed = JSON.parse(text);
+    return parsed && typeof parsed === 'object' ? parsed : null;
+  } catch {
+    return null;
+  }
+}
+
+export function parseCursorAgentStreamJsonEvents(stdout) {
+  const events = [];
+  for (const line of String(stdout ?? '').split('\n')) {
+    const parsed = parseStreamJsonLine(line);
+    if (parsed) events.push(parsed);
+  }
+  return events;
+}
+
+export function normalizeCursorAgentUsage(raw) {
+  if (!raw || typeof raw !== 'object') return null;
+  const inputTokens = Number(raw.inputTokens ?? raw.input_tokens ?? 0);
+  const outputTokens = Number(raw.outputTokens ?? raw.output_tokens ?? 0);
+  const cacheReadTokens = Number(raw.cacheReadTokens ?? raw.cache_read_tokens ?? 0);
+  const cacheWriteTokens = Number(raw.cacheWriteTokens ?? raw.cache_write_tokens ?? 0);
+  const billableInput = inputTokens + cacheWriteTokens;
+  const billableOutput = outputTokens;
+  if (billableInput <= 0 && billableOutput <= 0) return null;
+  return {
+    inputTokens: billableInput,
+    outputTokens: billableOutput,
+    cacheReadTokens: cacheReadTokens > 0 ? cacheReadTokens : 0,
+    cacheWriteTokens: cacheWriteTokens > 0 ? cacheWriteTokens : 0,
+  };
+}
+
+export function parseCursorAgentUsage(stdout) {
+  const events = parseCursorAgentStreamJsonEvents(stdout);
+  for (let index = events.length - 1; index >= 0; index -= 1) {
+    const event = events[index];
+    if (event?.type !== 'result') continue;
+    const usage = normalizeCursorAgentUsage(event.usage);
+    if (usage) return usage;
+  }
+  return null;
+}
+
+function extractAssistantText(message) {
+  if (!message || typeof message !== 'object') return '';
+  const content = message.content ?? message.message?.content;
+  if (typeof content === 'string') return content.trim();
+  if (!Array.isArray(content)) return '';
+  return content
+    .map((part) => {
+      if (!part || typeof part !== 'object') return '';
+      if (part.type === 'text') return String(part.text ?? '').trim();
+      return '';
+    })
+    .filter(Boolean)
+    .join('\n')
+    .trim();
+}
+
+export function extractCursorAgentDisplayText(stdout) {
+  const events = parseCursorAgentStreamJsonEvents(stdout);
+  for (let index = events.length - 1; index >= 0; index -= 1) {
+    const event = events[index];
+    if (event?.type === 'result') {
+      const resultText = String(event.result ?? '').trim();
+      if (resultText) return resultText;
+    }
+    if (event?.type === 'assistant') {
+      const assistantText = extractAssistantText(event.message ?? event);
+      if (assistantText) return assistantText;
+    }
+  }
+  return '';
+}
+
+export function buildCursorBillingTokenState(usage, priorBillingState = null) {
+  const normalized = normalizeCursorAgentUsage(usage);
+  if (!normalized) return null;
+  const priorIn = Number(priorBillingState?.lastInputTokens ?? 0);
+  const priorOut = Number(priorBillingState?.lastOutputTokens ?? 0);
+  return {
+    accumulatedInputTokens: priorIn + normalized.inputTokens,
+    accumulatedOutputTokens: priorOut + normalized.outputTokens,
+  };
+}