feat(browser): 增加 sequence 组合块能力

新增单层 sequence 容器以组合现有 orchestration blocks，并补充 sequence 内失败定位能力。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/mcp/ccs-browser-server.cjs

@@ -2438,6 +2438,9 @@ function formatOrchestrationSummary(session) {
     `error: ${session.error || 'none'}`,
     `status: ${session.status}`,
   ];
+  if (session.failedSequenceStepIndex !== null && session.failedSequenceStepIndex !== undefined) {
+    lines.push(`failedSequenceStepIndex: ${session.failedSequenceStepIndex}`);
+  }
   if (session.errorDetails?.failedAssertionIndex !== undefined) {
     lines.push(`failedAssertionIndex: ${session.errorDetails.failedAssertionIndex}`);
     lines.push(`field: ${session.errorDetails.field}`);
@@ -2523,6 +2526,7 @@ const SUPPORTED_ORCHESTRATION_BLOCK_TYPES = new Set([
   'wait_for_then_press_key',
   'run_replay_sequence',
   'assert_query',
+  'sequence',
 ]);
 
 const SUPPORTED_ASSERTION_OPERATORS = new Set(['equals', 'contains', 'gt', 'gte', 'lt', 'lte']);
@@ -2669,6 +2673,21 @@ function validateOrchestrationBlock(block) {
   }
 }
 
+function requireSequenceSteps(block) {
+  const steps = Array.isArray(block.args?.steps) ? block.args.steps : null;
+  if (!steps || steps.length === 0) {
+    throw new Error('sequence steps must be a non-empty array');
+  }
+  return steps;
+}
+
+function validateSequenceStep(step) {
+  validateOrchestrationBlock(step);
+  if (step.type === 'sequence') {
+    throw new Error('sequence does not support nested sequence blocks');
+  }
+}
+
 function normalizeRecordedEvent(pageId, event) {
   if (!event || typeof event !== 'object') {
     return null;
@@ -5116,9 +5135,28 @@ async function executeOrchestrationBlock(session, block) {
     return;
   }
 
+  if (block.type === 'sequence') {
+    await executeSequenceSteps(session, block);
+    return;
+  }
+
   throw new Error('unsupported orchestration block type');
 }
 
+async function executeSequenceSteps(session, block) {
+  const steps = requireSequenceSteps(block);
+  for (let index = 0; index < steps.length; index += 1) {
+    const step = steps[index];
+    validateSequenceStep(step);
+    try {
+      await executeOrchestrationBlock(session, step);
+    } catch (error) {
+      session.failedSequenceStepIndex = index;
+      throw error;
+    }
+  }
+}
+
 async function executeOrchestrationBlocks(session) {
   for (let index = 0; index < session.blocks.length; index += 1) {
     const block = session.blocks[index];
@@ -5154,6 +5192,7 @@ async function handleStartOrchestration(toolArgs) {
     completedBlocks: 0,
     currentBlockIndex: 0,
     failedBlockIndex: null,
+    failedSequenceStepIndex: null,
     error: null,
     blocks,
   };